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03. Santa Clara Valley Water District:z5o ALneApEN EXP14'Y SAM 10SE, CA 957 ] D-3b8G 1 EU~h10ME (408y 2G5-26o0 EACIMtL6 (aagl 2Gb-0271 v~ww,volloYwate r.org n w vaunt oPPOattn.tm' e.trtottfa PATfiICK 5. KWOK, P.E DIFECTf,H~, pl$r~l~•r Honorable drrfn Mahoney Vice Mayor _ ~ . City Of CuperNna i 0300 Torre Ave. Gt~pertino, CA 950'i4-3232 . Re: Permanents Creek Flood Protection Projec# Vice Mayor It~ahoney, As a member of the District's Lower Peninsula_ Watershed advisory Committee. f would like to offer your City Council a presentation or u~orifshop on the Permanents Creek Flood Protection Project, and'•inform you that District staff will be presenting the Pem~anertte Creek Planning Study to the District's Board in late ~5eptember or early October. • In February 2008,. the bistrict offered to conduct a ~iorkshop and~or give a presentation on the flood protection project to all the Cities with an interest in this flood protection protect; includ'mg the Gity of Cupertino. Since; then, we have conducted a workshop far the City of Mountain View, made a presentation to the City of Los Altos, and have discussed the project with Distr#ct >/ive Santa Clara County Supervisor Liz Kniss. • If you would like to receive a presentation or worl~hop, or have questions regarding the protect in general, please contact the District's Lower Peninsula Watershed Manager, Beau Gaidie, at (408} 265-2fi07, extension 2634. ~~ Patrick S. Kwok, 'P. E. . Director, Dis#rict 5 cc: Board of Dlrectots {?), O, Martin Steele, J. Fiedler, R. Callender, M. Rutz, B. Gaidie, K. Oven, S, Hosseini, Hon. Dotty Sandoval, Hon. Kris Wang, Hon. Gilbert Wong, Hon. Mark Santoro Tito mission of }he; 5drriu Cfcac Valley Wcrtcr flisfrid (s a health 13 -1 . stewardghi Y. ~~ and enhanced quartfy of Ewing in Santq Clara Couhfy #rough vrafersl,ed p and comprehen,iYC management of v+eEc~` resourr~ In a prpcy3cdl, ~osfi-efFecFiv~ or+d ortviranmenta!!y serts•tive manner_ EXHIBITS BEGIN HERE ~~/q-~G-08 ~`3 Clean, Safe Creeks =ti ~ ~~ a5 ~ ~;: oa. .e ~; , :~'~ ~'* ~:-. -. ~ _ ~ 11 t,~ . ~. Santa Clcarca Valley Water District 'v 3 a co co n co 0 n O~ -z _O CD t~ flood rotection ro'ect nente Cree Per111q ~ ~rotect~ ~g people l Permanente Creek has a history of flooding, having experienced major flooding in 1862, 191 1, 1940, 1950, 1952, 1955, '~ 1958, 1963, 1968, 1995 and 1998. Flooding can result in millions of dollars / / ~ © in damage to homes, businesses and i b d nesses us isruption to schools. In addition, and transportation networks can result in 1 significant loss Of productivity and revenue. '~d/efe/d One of the project's goals is to avoid utility 'uo' ~~:' ~ and transportation shutdowns and prevent ~' potential damages that could exceed $48 l 1999 ll ,~; <em ue). va ion ( mi ~J ~o~ fxpy, <o~f Each winter, thousands of households, r F/<on~; °'osi b schools and businesses in Mountain View ~ no~eo/ ' ~~ ~° ~ and Los Altos are susceptible to flooding o { ° h ¢, ` ~ Q from Permanente Creek during a major t t i Di W ll l ' ~' o r c ater s ey ara Va storm. The Santa C Almond Ave a~` ~ has initiated planning of aflood-protection -~'' p,~, ~ project along 10.6 miles of Permanente ` yro°~~ ~ Creek, from San Francisco Bay's southwest ~ shoreline through Mountain View to Foothill ' Cuesta Dr LEGEND c Expressway in Los Altos. _ ~ ---- y Project features Floodwalls _ ~ Levin Ave _~ our Clean, Safe O Creek restoration ~ ^ Park detention l M K ' e ~ i ~~ ~ ~S ~© © vey c e erm~nente 4 `,~, 1 G ! O Channel widening '~d ~ l3iYEfS~Gn o thannei ' The project is Q y ~ Cuesta Park detention l ~ funded by the © Permanente bypass channe ~ o Clean, Safe Creeks _ _ _ - >r.~ ® Hale bypass channel ~ ~ ° ® and Natural Flood : . ~ © New diversion structure ~~ Of~// s~ Park detention "°hy ~ t i A h S R ' _ Protection parcel b`~ taX assed b ~ "'~'' p y ® on o an n anc o South Branch Dam ;t ~ ~ ~~ voters countywide ' ' `-~'~t, in November ,'~~f w:-'~ _ Bloch School detention 2000. The15-year Lan dmarks plan makes it possible to protect homes, Shoreline Park schools and businesses from floo ing, ® Mountain View City Hall improving the health of creek and bay Los Altos City Hall ecosystems and creating trails and parks for EI Camino Hospital feCreatlOnal enjoyment. 1 % Flood Limits ~y rn e n u m oe rs The Clean, Safe Creeks plan provides $27 million to design and construct a project to: • Provide natural flood protection for 1,664 properties by 2016; • Prevent flooding of Middlefield Road and Central Expressway; • Prevent potential damages in excess of $48 million. All dollar figures are 1999 value. The water district is working with the cities and their residents through community and project task force meetings to develop conceptual designs. Comments and feedback have helped to identify 1 1 feasible flood-protection alternatives for further study. The alternatives employ different methods of flood protection, including: • Flood-peak reduction, such as detention basins and dams; • Bypass channels; • Channel improvements, such as floodwalls and channel-widening; • Flood-proofing, such as elevating structures or relocating them out of the flood-prone area. Some of these alternatives provide opportunities to: • Protect 3,170 parcels • Remove as many as 2,300 feet of concrete channel to restore to a more natural stream condition • Provide more parks and preserve 20 acres of open space, both in Cuesta Annex and in Rancho San Antonio County Park • Reduce creek erosion • Enhance eight acres,of wildlife habitat • Preserve 1.6 miles of riparian habitat along Permanente and Hale creeks • Extend the existing Permanente Creek trail beyond U.S. 101 to Middlefield Road Looking ahead The Permanente Creek Flood Protection Project offers a tremendous opportunity for amulti-purpose project to improve flood protection, create recreational opportunities and enhance the environment. The water district will continue to work with the cities and the community to identify the most suitable alternative. No matter what alternative or combination of alternatives is finally chosen, the water district is looking forward to working with the community to provide critical flood protection needs for Mountain View and Los Altos. Project schedule 2004 2006 2008 2010 2012 2014 2016 ~ ~ ~ , ~ ~ Preserving the existing riparian habitat along Permanente Creek is one of the project's objectives. The pro"ect on Permanente Creek includes removal of as many as 2,300 ~eet of concrete channel (left). The artist's rendering (right) shows the creek in a restored, more natural condition, such as this location north of Middlefield Road in Mountain View. _. EY. _. r,ee .., 7t For more information, contact Senior Project Manager Saeid Hosseini at (408) 265-2607, ext. 2680, or email shosseini@valleywater.org. Also, visit our website at and use our customer request and information system. With three easy steps, you can use this service to find out the latest information on the project or to submit questions, complaints or compliments directly to a district staff person. Use Access Valley Water to search for projects or work going on in your neighborhood. What we do The Santa Clara Valley Water District manages water resources and provides stewardship for the county's five watersheds, including 10 reservoirs, hundreds of miles of streams and groundwater basins. The water district also provides flood protection throughout Santa Clara County. Visit our website, www valleywater.org Neighborhood work Flood protection also includes smaller neighborhood projects to keep creeks in good shape. The water district removes sediment, invasive vegetation, trash and debris, and repairs eroded creek banks to help our waterways carry floodwaters safely away from nearby homes and businesses. This same work also creates more natural conditions for fish, plants and wildlife. On the cover: 1. Flooding from Permanence Creek at Bloch School in March 1983 2. Permanente Creek at Shoreline Park at Mountain View. 3. Red-winged blackbird (Agelaius phoeniceus) on Guadalupe River in San Jose. 4. Great egret (Casmerodius albus) at Shoreline Park in Mountain View. 5. Long-billed curlew (Numenius americanus) at Shoreline Park in Mountain View 6. Trail adjacent to Camden Groundwater Recharge Ponds in Campbell. 1 2 0 3 3 5 4 0 6 0 r UK:' ~ICUmemA .j, / II yWeer := tl r~~le q lien ~pla nG d I ~_r[ d-e 'hm Ne Access ValleyWatar ~ nc t itp r o r nnep a v Imy Wier. r,llw~r three easy steps Szrd us your requr;t., gU2AI0f15, :CfT' ^~a ft`~ ~ I i'~: nposz a [epic antl ;ub[csic that match?=_ re subject or ;~nur 3P~CCI71p~1; 112^.L ^l 0e,cribe your request ~ ~ 3) :reate 3n ac.runt sa you ran track the status anu any r?spnnses unhne, '_4 halr a day,' days 3.v?el; bVe hupe yule ei guy [hls ;ervu:e and ~uve Inr~l: fnrvw•ani In yettirud hack to ynu lm wuni. dl bgri, . i~~i ilr...wi" ~ Lu.i ;,ill..; W.a., Pi,nni ow<. ~.aba-_as-. u ~vhngcr Road E~. LI.: ~ ~.,-i~~,.n uonl .. .-- „J,I.,F.. r• e i.. ,I.,. ~„ i ,~ 'SOrH~w 3; eel 2 n. _ ~i~anul:e F er -~ .il .~ v n ~ n mela San Juaa ehVUrl ~hburhaad woilc ~ Coynte Natar;hed ,.nlfn ~ Ve~'ihnrhnnd vunrk-~uadalnpa ~~V:.tarched anberhea.l -v9M Lo.vrrF'cnin.ulvV~/e~: 'v'alley •/Y.ater~M1Cds ' ~. ~baihood wore ~!%ua>W~alei:hed You're in a watershed No matter where you are, you're in a watershed. A watershed is the area ~.• of land that drains a common waterway. In Santa Clara County, our creeks catch rain and runoff from storm drains and carry 1 water north to San Francisco , to Monterey Bay. Along the way, some of the water is used to fill reservoirs for drinking water, replenish the underground aquifer and create better habitat for fish and wildlife. This project is in the Lower Peninsula Watersheds, a 98-square-mile area with many small-creek watersheds that feed the tidal wetlands along San Francisco Bay. Its San Francisquito and Stevens creeks are among the last remaining viable steelhead trout runs in the county. Santa Clara Valley Water DistricE 5M 5750 Almaden Expwy San Jose, CA 951 18 www.valleywater.org Permanente Creek Flood Protection Project District Contact Information Access Valley Water: www.valleywater.ore Afshin Rouhani Saied Hosseini Project Manager Senior Project Manager Capital Project Services Division Capital Project Services Division 5750 Almaden Expressway 5750 Almaden Expressway San Jose, CA 95118 San Jose, CA 95118 (408) 265-2607 extension 2616 (408) 265-2607 extension 2680 e-mail: arouhani@valleywater.o~r e-mail: shosseini~valleywater.~r Beau Goldie Rick Callender Deputy Operating Officer Assistant Operating Officer Watershed Operations Government Relations Unit 5750 Almaden Expressway 5750 Almaden Expressway San Jose, CA 95118 San Jose, CA 95118 (408) 265-2607 extension 2634 (408) 265-2607 extension 2017 e-mail: b~oldie@valleywater.org e-mail: rcallender@valleywater.u:; Olga Martin-Steele Director Patrick Kwok Chief Operating Officer Director -District 5 5750 Almaden Expressway 5750 Almaden Expressway San Jose, CA 95118 San Jose, CA 95118 (408) 265-2607 extension 2326 (408) 265-2600 e-mail: osteele@valleywater.or~ 0 c~ m ~ m -~ ~ ~ o ~ ~ ~ a~ ~ i c o ~ c c ~~ ~ E c ~ ~ U ~ .~ O ~ N +' ~ cn C QC'7 '~ ff3 ~ U ~ ~ ~ X O O ~ ~ ~ ~ ~ p .~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ _ _ (~ Q ~ '~ ~ ~ ~ ~ ~ ~ / V Q ~ ~ Q. 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Z ~'."'"_,_._. ,. ~ t ~ ry ~~ ~, x n t ~y d ~ ~ikF ~ ~ ~ ~ v $~ N M ~ ^ A ~-.+ • ~ ~ ^ W L O ^ Y..L •~ O i--~ W ~ ^ ' /I i4: W ^` ~ U ~ ~ ~ ~ ~ ~ _ ~ W (n C ~ (/7 o c a ~ o o ~ ~ ~ ~ ~ ~ ~S n ~ ~' ~ ° m N m N ~ ~ ~ .. ~ x N N 61 O (D tD ~ ~ ~ ~ _ ~ ~~ oa n m ~~ ~~ ~ ~ ~ ~ ~o x Q N .~, ~ ~ ~o ~ o D ~ (~ =x# ~ ~. t:. -° _ -. o m ~ ~ ~ ~ Q~ .._ ~ cn t~ _ _ £` ~' m O~ ii Q ~v Q N U 0 Q C 0 ~' +-~ O N r O N M r i O N ° N r O , N r O N O O 'a N ~ O N r^ V / ~ N ,~.~ ~ ~ o N s a • ~ c ~c ~ Q O m L N a a 0 0 N ce 9130%~ #~ Permanente Creek Flood Protection Project Planning Study Report ~ P ~I+f>-fir L .C `~~6I~ •f .»..aM4r~~x 4 ~'~"'J~ s #~r. ~h'~~. ., v"im"' h 'yL~u $ :ti y~ .., .. _, .. b ,. ~, , .. .., a `,} =r ~ _, b14 ^ _ ~'s;'~''. _ ~. ~~ _~ i_ _ w ~~ ter, ~" r r «~'!~ _ ,,R, , _ .. ~. ~" ~r ~. ;. s~ .~ .. ~~ - ~.i' •1, ~ , r .ate July 2008 Santa Claro Valley Water District SanEa Clara Volley Water District PERMANENTE CREEK FLOOD PROTECTION PROJECT PLANNING STUDY REPORT PROJECT NO. 10244001 Prepared by Capital Program Services Division Afshin Rouhani, P.E. Project Manager Saeid Hosseini, P.E. Senior Project Manager Katherine Oven, P.E. Assistant Officer Nai Hsueh, P.E. Beau Goldie, P.E. Chief Operating Officer Deputy Operating Officer Office of AGM -Capital Lower Peninsula Watershed Olga Martin-Steele Chief Executive Officer JULY 2008 DISTRICT BOARD OF DIRECTORS Rosemary C. Kamei, Chair District 1 Patrick S. Kwok, P.E. District 5 Joe Judge District 2 Tony Estremera At Large Richard P. Santos District 3 Sig Sanchez, Vice Chair At Large Larry Wilson District 4 SANTA CLARA VALLEY WATER DISTRICT PERMANENTE CREEK FLOOD PROTECTION PROJECT PLANNING STUDY REPORT PROJECT NO. 10244001 Prepared by Capital Program Services Division: Afshin Rouhani, P.E. Associate Civil Engineer Gabriel Vallin Assistant Civil Engineer Saeid Hosseini, P.E. Senior Project Manager Katherine Oven, P.E. Assistant Operating Offier JULY 2008 This Planning Study Report has been prepared under the direction of the undersigned, who hereby certifies that he is a registered engineer in the state of California. Afshin Rouhani, RCE No, C54554, Exp. Date: 12/31/2009 ACKNOWLE[)GEMENTS This document was prepared with assistance from: SANTA CLARA VALLEY WATER DISTRICT Beau Goldie, P.E. Deputy Operating Officer, Watershed Manager Katherine Oven, P.E. Assistant Operating Officer Saeid Hosseini, P.E. Senior Project Manager Afshin Rouhani, P.E. Project Manager Gabriel Vallin Assistant Civil Engineer Metro Ulloa Assistant Civil Engineer David Dunlap Senior Environmental Planner Kurt Lueneburger Project Environmental Planner Liang Lee, P.E. Unit 1~lanager, Hydraulics Debra Caldon Unit I~lanager, Environmental Planning Jim Wang, P.E. Unit P~lanager, Hydrology Mike Munson, P.E. Unit PJlanager, Structural Bill Springer, P.E. Senior Engineer, Watershed Operations Lisa Porcella Bioto~~ist Mohammad Khan, P.E. Senic-r Engineer (Geotech) Eric Tsou, P.E. Senic-r Engineer (Structural) Tri Nguyen, P.E. Asso~~iate Civil Engineer Wendy Chang, P.E. Asso~:iate Civil Engineer Nahm Lee Assistant Civil Engineer Kristen O'Kane Envir~~nmental Planner, Watershed Operations Richard Volpe, P.E. Senic-r Engineer Jim Nelson Senic-r Engineering Geologist Lee Ellis Project Coordinator Merna Leal Project Coordinator Tamra Zozaya Project Assistant JONES AND STOKES ASSOCIATES (ENVIRONMENTAL CONSULTANT) Kevin MacKay Anna Buising Project Manager Project Manager PERMANENTE CREEK PROJECT TASK FORCE Donald Andersen John Benza Vivian Blomenkamp Dennis Buranek Gloria Burke Warren Carlson Henry Cooper Susan Culazzo Linda DeMichiel Ali Gharibian Permanente Creek Flood Protection Project Page i Planning Study Report July 2008 Mike Hammes Rex Hinkle Tom Horan Bob Kagiyama Larry Lang Sue LaTourrette Leland Lera Larry Lind Libby Lucas Steve McSharry Tim Sandis Tracey Schwartz MOUNTAIN VIEW SAVE OPEN SPACE: Kevin McBride Justine Fenwick Permanente Creek Flood Protection Project Page ii of 144 Planning Study Report July 2008 TABLE OF CONTENTS Page EXECUTIVE SUMMARY ...................................................................................................... ES-1 CHAPTER 1 BACKGROUND ...............................................................................................1 1.1 Project Background ...............................................................................1 1.2 Purpose of the Planning Study Report ................................................1 1.3 Study Overview ..................................................................................2 1.4 Goals and Objectives of the District ....................................................2 1.5 Project Objectives ..............................................................................4 1.6 Previous District Engineering Studies and Projects ............................... 4 1.7 Previous Studies and Actions by Other Agencies ..................................7 1.8 Cities and Other Major Pro~~erty Owners Within the Watershed ...........7 1.9 The Recommended Capital Improvement Project ...............................10 CHAPTER 2 WATERSHED DESCRIPTION .......................................................................15 2.1 Watershed Description ........................................................................ 15 2.2 Creek Descriptions .............................................................................. 15 2.3 Watershed Hydrology .......................................................................... 24 2.4 Watershed Physiography ar~d Geology ............................................... 24 2.5 Historical Stream Channel ................................................................... 26 2.6 Land Subsidence ................................................................................ 29 2.7 Summary of Environmental Setting ..................................................... 29 CHAPTER 3 PROBLEM DEFINITION .................................................................................33 3.1 Creek Flooding ....................................................................................33 3.2 Local Drainage Conditions .................................................................. 42 3.3 Maintenance Access ........................................................................... 42 3.4 Erosion and Sedimentation .................................................................43 3.5 Structural Deterioration of Previous Work ............................................48 3.6 Permanente Diversion Flow Split ........................................................48 3.7 Sea Level Rise .................................................................................... 51 CHAPTER 4 FORMULATION OF ALTERNATIVES ...........................................................53 4.1 Alternatives Approach ......................................................................... 53 4.2 Conceptual Project Elemenis ............................................................ .. 53 4.3 Conceptual Project Elements Development ...................................... .. 55 4.4 Conceptual Alternatives Development ............................................... ..58 4.5 Conceptual Alternatives Screening Methodology .............................. .. 86 4.6 Feasible Alternatives Description ...................................................... .. 87 4.7 Alternative Ranking Method~~logy ...................................................... 103 4.8 Staff Recommended Altern<<tive Selection ........................................ 106 Permanente Creek Flood Protection Project Page iii Planning Study Report July 2008 Page CHAPTER 5 PROJECT OUTREACH ................................................................................117 5.1 Public Meetings .................................................................................117 5.2 Permanente Creek Task Force .........................................................117 5.3 Outreach to Cities and the County .....................................................118 5.4 Resource Agencies ...........................................................................119 5.5 Meetings with Watershed Stakeholders ............................................119 CHAPTER 6 RECOMMENDED PROJECT .......................................................................121 6.1 Design Basis ..................................................................................... 121 6.2 Recommended Project ......................................................................121 6.3 Right-of-Way Requirements ..............................................................134 6.4 Best Management Practices ..............................................................135 6.5 Climate Change ......................................................................135 CHAPTER 7 MAINTENANCE PROGRAM ........................................................................137 7.1 Maintenance History .........................................................................137 7.2 Continuing Project Maintenance Activities .........................................139 7.3 Maintenance Activities for New Project Elements ..............................140 7.4 Long Term Infrastructure Maintenance ..............................................143 7.5 Maintenance Cost ............................................................................. 143 CHAPTER 8 PROJECT COST, FUNDING, AND SCHEDULE ..........................................145 8.1 Project Cost ......................................................................................145 8.2 Project Funding .................................................................................146 8.3 Project Schedule ...............................................................................146 CHAPTER 9 CONCLUSIONS AND RECOMMENDATIONS .............................................147 Permanente Creek Flood Protection Project Page iv of 144 Planning Study Report July 2008 LIST OF APPENDICES,1'ABLES AND FIGURES Appendices A Conceptual Alternative Figures B Feasible Alternatives Maps C Organizations and Persons Contacted During Preparation of This Report D Bibliography E Detailed Cost Estimate F Natural Flood Protection Ratings C~etails G The One-Percent Flood H Engineering Drawings of Recommended Project (bound separately) I Hydrology Report J List of Technical Terms and Acrorn,rms K Persons to Contact for More Information Tables Page Table 2.1 Watershed Design Flow Values..... .................................................................. 24 Table 3.1 Manning's n Factors ........................................................................................ 37 Table 3.2 Creek Reach Capacities ..............., .................................................................. 39 Table 4.1 Conceptual Alternatives Level I Sc~~eening ..................................................... 109 Table 4.2 Summary of Feasible Alternatives ................................................................. 111 Table 4.3 Feasible Alternatives NFP Objectives Ratings ............................................... 113 Table 4.4 Recommended Alternative Selection Table ................................................... 115 Table 6.1 Design Flows Pre- and Post-Projec;t .............................................................. 121 Table 8.1 Summary of Design/Construction C:osts ........................................................ 145 Figures Figure P1 Staff Recommended Alternative ................................................................... ES-4 Figure 1.1 Permanente Watershed and One-Percent Floodplain .....................................12 Figure 1.2 Reach Map .....................................................................................................13 Figure 2.1 Typical Photo of Reach P1 ............................................................................. 16 Figure 2.2 Typical Photo of Downstream Portions of Reach P2 ....................................... 17 Figure 2.3 Typical Photo of Upstream Portion:~ of Reach P2 ........................................... 17 Figure 2.4 Typical Photo of Reach P3 ............................................................................. 18 Figure 2.5 Typical Photo of Reach P4 Between the Culverts ........................................... 19 Figure 2.6 Typical Photo of Reach P5 ............................................................................. 19 Figure 2.7 Typical Photo Along Reach P6 ....................................................................... 20 Figure 2.8 Typical Photo Along Reach P7 ....................................................................... 20 Figure 2.9 Typical Photo for Reach P8 Downstream of Portland Avenue ......................... 21 Figure 2.10 Typical Photo for Reach P8 Upstream of Portland Avenue ............................. 21 Figure 2.11 Typical Photo of Reach H1 ............................................................................. 22 Permanente Creek Flood Protection Project Page v Planning Study Report July 2008 Page Figure 2.12 Typical Photo of Reach H2 .............................................................................22 Figure 2.13 Typical Photo of Reach PD (Trapezoidal section) ........................................... 23 Figure 2.14 Typical Photo of Reach PD (U-Frame section) ...............................................23 Figure 2.15 San Francisco San Jose Railroad, Allardt, 1862 .............................................27 Figure 2.16 City of San Jose, Hare, G.H. 1872 .................................................................28 Figure 2.17 Subsidence in Santa Clara County ................................................................. 30 Figure 3.1 Recent Flooding ............................................................................................. 34 Figure 3.2 FEMA and District Floodplains ........................................................................38 Figure 3.3 Sediment Removal Locations .........................................................................46 Figure 3.4 Channel Types ...............................................................................................49 Figure 3.5 Remaining Service Life ...................................................................................50 Figure 6.1 Floodwalls ..................................................................................................... 123 Figure 6.2 Riparian Restoration and Trail Extension ...................................................... 124 Figure 6.3 McKelvey Park .............................................................................................. 127 Figure 6.4 Cuesta Park Annex ....................................................................................... 129 Figure 6.5 Cuesta Park Annex ....................................................................................... 130 Figure 6.6 Cuesta Park Annex ....................................................................................... 131 Figure 6.7 Rancho San Antonio ..................................................................................... 133 Figure 7.1 Sediment Removal 1980-2000 D/S of Hwy 101 ............................................137 Figure 7.2 Sediment Removal 1983-1999 Permanente Diversion ..................................138 Permanente Creek Flood Protection Project Page vi of 144 Planning Study Report July 2008 EXECUTIVE SUMMARY Introduction The Santa Clara Valley at one time supported extensive riparian vegetation and wildlife along the banks of the Lower Peninsula watersheds. Tfie banks of the Permanente and Hale Creeks, prone to regular flooding, supported a diverse and biologically rich habitat. As the valley portions of the watershed were converted to farm: and orchards, the creeks were significantly altered. The creek floodplains were converted to farms and then to urbanized use. Flooding became a major problem in the watershed. The Permanente watershed has a history of recurring floods which have adversely impacted the safety and economic stability of the residents and businesses within the floodplain. Flooding in the watershed has been documented as far back as 1862. Other floods were recorded in 1911, 1940, 1950, 1952, 1955, 1958, 1963, 1968, 1983, 1995, and 1998. This report presents the flood-related problems in the Permanente Creek watershed. This capital improvement project was initiated as part c,f the Clean Safe Creeks program, approved by the voters of Santa Clara County in 2000. Based on the District's Ends Policies, a variety of alternatives that would satisfy the project objectivE~s were evaluated. The alternatives were assessed for feasibility and broad environmental impacts. To ensure all concerns were addressed, the recommended alternative was developed in coordination with the cities of Mountain View, Los Altos, and Cupertino, Santa C-1ara County, resource agencies, stakeholders, and the citizens residing in and owning properties adjacent to recommended project impact areas. The recommended project ~nras selected because it best served the interests of the public and met the District Board of Director's Ends Policies. This report is prepared in accordance with the District Act, which directs the preparation of plans for a project and reports to be filed with the Board.. To comply with the California Environmental Quality Act, an Environmental Impact Report will k-e prepared to address the recommended project's environmental impacts. Project Objectives The project objectives were developed to meet thE~ flood protection commitments made in the Clean, Safe Creeks (CSC) measure. These objectives included the following: • Provide flood protection to 1,664 parcels downstream of EI Camino Real from a 100- yearflood; • Prevent the flooding of Middlefield Road ar~d Central Expressway; • Develop an asset protection plan for the dE~teriorating concrete channels built previously; • Develop guidelines for long term maintenance of the facility; and • Minimize the cost for maintenance. Permanente Creek Flood Protection Project Page ES-1 Planning Study Report July 2008 Project Alternatives A thorough range of potential alternatives were reviewed. Twenty-six conceptual alternatives were identified. These included no-project, structural, flood detention, floodproofing, and restoration alternatives. The conceptual alternatives were analyzed for whether they met the project's objectives, were technically buildable, were affordable, and had available right-of-way. The alternatives were thus winnowed to twelve feasible alternatives, which included structural and flood detention alternatives. These feasible alternatives were rated using Natural Flood Protection objectives and compared with each other. The best rated alternative was selected as the staff-recommended alternative. Public Outreach Community feedback and support was actively sought during the project planning process of the project. The District created a Permanente Creek Task Force composed of local citizens and staff from the affected cities to assist the project team in planning decisions. The District also held several public meetings at various local venues to discuss the project planning process and gather public input. District staff made several presentations to the city councils of Mountain View, Los Altos, and Cupertino and the County Board of Supervisors to inform them of project progress and seek feedback. District staff has also met with resource agencies and various local stakeholder groups. Staff-Recommended Alternative After reviewing the feasible alternatives using Natural Flood Protection objectives, engagement with the community, and feedback received from citizens, the Permanente Task Force, City staff, and elected officials, District staff has identified Alternative Z as the staff-recommended alternative for the Board's consideration. This alternative best meets the project's objectives and the Board's Ends policies. This alternative is composed of the following project elements (see Figure P1 for map): Offstream flood detention facilities in: o Rancho San Antonio Park o Blach Jr. High School o Cuesta Park Annex o McKelvey Park • Bypass channel along Hale Creek • Bypass channel connecting Blach detention and Cuesta Annex detention • Channel widening along reaches of Permanente Creek and Hale Creek • Floodwalls north of Highway 101 on levee channels • Anew diversion structure at the Permanente Diversion Permanente Creek Flood Protection Project Page ES-2 Planning Study Report July 2008 There will be an opportunity for restoration, habitat enhancement, and trail extension upstream of Highway 101 for the Board's consideration. Estimated Project Cost, Financing, and Schedule The estimated capital cost for the recommended alternative is $58 million in 2008 dollars. The overall (including current effort) current value maintenance cost for the 50-year project length is $22 million. The optional restoration project element would cost $3.5 million. Thus, the overall project cost in 2008 dollars would be $84 million. Not all of the recommended alternative's elements are needed to meet the CSC measure's protection level. Two of the project elements needed for the overall watershed plan could be built at a later date. This would reduce the project's current capital cost to $40 million. The project's capital budget is approximately $38.6 million. Project design would be conducted in phases, based on work complexity and outreach effort needed. The design would be conducted from 2009 through 2011. Construction activities for some project elements could commence in 2010, with the entire project completed by 2015. Project Implementation If the Board elects to accept the staff recommended alternative and authorize work to continue, the following milestones would be the next steps followed: • Draft Environmental Impact Report (DEIR) in winter 2008; • Final project planning report and EIR in spring 2009; • Certification of EIR and approval of the project planning report in summer 2009; • Construction commencement in 2010. Permanente Creek Flood Protection Project Page ES-3 Planning Study Report July 2008 Figure P1. Staff Recommended Alternative F;codv~:ails 101 ~ i i Palo Atto Potential I' Riparian Restoration ~roaiP ~P ~a V ~ Ro. Alternative Z Parcles Protected 2220 Mt. View 250 Los Altos Parcels Remaining 520 Mt. View 180 Los Altos Nbuntain View Los Attos P m oc` ~~~,~ ~Ql McKelvey y Park ' ~~ Channel v Widening /~ r FCC J~'O RO j ai a il3ltrlcl - '` Wideninc; c 0 ~ Cuesta Park ~. Annex Cuesta Dr ... Permanente (~ ~ ' Bypa55 z Sunnyvale ~ ! `c ` CovfngtonRd ` 17 Blach School Hale ; R`~r-""~`~ ~ N Di i PRELLAINARY ew vers on ,~~_a;, Structure Rancho San Antonio _- Permanente Creek Flood Protection Project Page ES-4 Planning Study Report July 2008 CHAPTER 1 BACKGFtOUND The Permanente Creek Flood Protection Project's, Planning Study Report (PSR) presents the existing flood protection problems in the Permanente Creek watershed. The PSR addresses the impacts of the potential flooding on the Cities ~~f Los Altos and Mountain View. The PSR includes a discussion of the alternatives analyzed, and a recommended capital improvement project. An Environmental Impact Report (EIR) will be prepared separately and contain a discussion of the environmental impacts of, and rriitigation for the recommended project. Public hearings will be held on the PSR and the EIR. Comments will be solicited from the community and responsible agencies. The Santa Clara Valley Water District (District) Board of Directors (Board) will then decide what action, if any, to take. 1.1 Project Background Recurrent flooding along Permanente and Hale Creeks presents a long term hazard to public health and safety, property values, and economic stability in the Cities of Los Altos and Mountain View. Hydraulic models of Permanente and Hale Creeks have shown that more than 3,000 parcels would likely be subject to flooding iri aone-percent event (Figure 1.1 -Watershed Flood Map). Flood protection structures constructed in the 1960's have deteriorated and thousands of feet of concrete channels need to bE~ repaired or replaced. As part of the Clean, Safe Creeks (CSC) and Natural Flood Protection Program (projects funded by the voter-approved Measure B in November 2C-00), the District initiated the Permanente Creek Flood Protection Project study to identify flc-od protection, maintenance, structural repair, and habitat restoration opportunities within the watershed. 1.2 Purpose of the Planning Study Report This report has been prepared in accordance with the District Act. The report includes the following: • Background information and project goals and objectives (Chapter 1) • Watershed description (Chapter 2) • Problem definition (Chapter 3) • Formulation of project alternatives (ChaptE~r 4) • Project Planning Outreach (Chapter 5) • Recommended project (Chapter 6) • Description of maintenance program (Chapter 7) • Project cost, funding, and schedule (Chapter 8) • Conclusions and recommendations (Chapi:er 9) In addition to this report, an EIR will be prepared t~~ address the environmental impacts of the recommended project. The EIR will contain a det~~iled discussion of the impacts and proposed mitigation measures. The EIR will support decision making by the District and other responsible and cooperating agencies to ensure compliance with the California Environmental Quality Act Permanente Creek Flood Protection Project Page 1 Planning Study Report July 2008 (CEQA). The District Board must consider these impacts before making its decision on the project to meet lead agency responsibilities. 1.3 Study Overview The recommended project proposes improvements from north of Freeway 101 to south of Freeway 280. To assist in discussion of project elements, the watershed has been subdivided into the following reaches (Figure 1.2 -Project Reaches): Permanente Creek: • Reach P1: From San Francisco Bay to Boat Pond Bridge • Reach P2: Boat Pond Bridge to Highway 101 • Reach P3: Highway 101 to Villa Street • Reach P4: Villa Street to upstream of EI Camino Real • Reach P5: Upstream of EI Camino Real to confluence with Hale Creek • Reach P6: Hale Creek to Cuesta Drive • Reach P7: Cuesta Drive to Permanente Diversion • Reach P8: Diversion to Foothill Expressway Hale Creek: • Reach H1: Confluence with Permanente Creek to Rosita Avenue • Reach H2: Rosita Avenue to Foothill Expressway Permanente Diversion is referred to as reach PD. Also, the creeks upstream of Foothill Expressway are referred as upper watershed reaches. A number of different alternatives would satisfy the objectives of the District and the affected communities. Each alternative was assessed for its ability to meet project objectives, affordability, and how well in met the Board's Ends Policy. 1.4 Goals and Objectives of the District The District is the water resource management agency responsible for meeting the flood protection and wholesale water supply needs of Santa Clara County's 1.8 million residents. The mission of the District is a healthy, safe, and enhanced quality of living in Santa Clara County through watershed stewardship and comprehensive management of water resources in a practical, cost-effective, and environmentally-sensitive manner. The District's goals are expressed through the Ends Policies adopted by the Board. These policies are: Water Supply: • There is a reliable supply of healthy, clean drinking water. • The water supply meets or exceeds all applicable water quality regulatory standards in a cost-effective manner. Permanente Creek Flood Protection Project Page 2 Planning Study Report July 2008 • The water supply is reliable to meet future demands in Santa Clara County, consistent with the County's and cities' General Plan; and other appropriate regional and statewide projections. • Baseline water supplies for Santa Clara C~~unty are safeguarded and maintained. • The integrity of the District's existing Water Utility infrastructure is maintained. • Imported water supplies and quality are pr~~tected and maintained. • Groundwater resources are sustained and protected for water supply reliability and to minimize land subsidence. • The groundwater basins are aggressively protected from contamination and the threat of contamination. • Water recycling is expanded within Santa Clara County in partnership with the community, consistent with the District's Integrated Water Resources Plan (IWRP), reflecting its comparative cost assessments and other Board policies. • Water conservation is implemented to the maximum extent that is practical. Flood Protection: There is reduced potential for flood damages. There is natural flood protection that balarn~es environmental quality, community benefit and protection from creek flooding in a cost effective manner. In providing flood protection, balance the following multiple objectives: Homes, schools, businesses, and t~•ansportation networks are protected from flooding and erosion. 2. Ecological functions and processes are supported. 3. Physical stream functions and processes are integrated. 4. Maintenance requirements. 5. Projects are integrated within the watershed as a whole. 6. The quality and availability of water is protected. 7. Cooperation with local agencies achieves mutually beneficial goals. 8. Community benefits beyond flood protection. 9. Life-cycle costs are minimized. Permanente Creek Flood Protection Project Page 3 Planning Study Report July 2008 Environmental Enhancement: • There is an enhanced quality of life in Santa Clara County through the protection and enhancement of watersheds, streams, and the natural resources therein. • Mitigations are implemented to protect watersheds, streams, and the natural resources therein. • Potential Mitigation banking opportunities are identified and implemented as determined appropriate by the Board. In identifying and selecting mitigation banking opportunities, emphasis shall be placed on the environmental benefits. • Environmental enhancements are implemented to improve watersheds, streams, and the natural resources therein. • Potential environmental enhancement opportunities are identified to the Board. • Environmental enhancement opportunities are implemented as determined appropriate by the Board. 1.5 Project Objectives The project's objectives are: • Develop a plan for the entire watershed that presents alternatives and a recommendation for providing flood protection for all flows up to the one-percent flood for Permanente Creek, Hale Creek, and the Permanente Diversion between Foothill Expressway and San Francisco Bay. • Identify opportunities for environmental enhancement such as stream restoration, as well as trails, parks, and open space for the Board consideration. • Provide flood protection to 1,664 parcels (1,378 homes, 160 businesses and 4 schools/institutions) downstream of EI Camino Real from a 100-year flood (saving potential damages in excess of $47.9 million). • Prevent flooding of Middlefield Road and Central Expressway. • Develop assets protection plan for the deteriorating facilities of the existing flood control channel along Permanente Creek and Hale Creek. • Development of guidelines for the long-term maintenance of the facility. • Minimize the cost for maintenance. 1.6 Previous District Engineering Studies and Capital Projects This section briefly describes previous District engineering studies, improvement projects, and major maintenance projects. Projects are described in chronological order. Permanente Creek Flood Protection Project Page 4 Planning Study Report July 2008 Permanente Diversion Channel In 1956, a "Preliminary Report on the Improvement of a Portion of Permanente Creek in Zone NW-1, Project 3" was prepared by Thelo A. Perrot Consulting Engineer for the Santa Clara County Flood Control and Water Conservation District. The report was prepared in response to the 1955 flooding, and proposed the construction of a diversion channel which would carry high flows from Permanente Creek to Stevens Creek. The concrete trapezoidal Permanente Diversion channel was constructed circa 1960. An earthen trapezoidal channel was also constructed on Permanente Creek downstream of Portland Avenue. The work is detailed in the 195~t "Permanente Creek Cross Channel" plans. Hale Creek Improvements In 1956, a "Preliminary Engineering Report, Hale Creek Improvement Project No. 9, Zone NW-1"was prepared by Don Reinoehl Consulting Engineers for the Santa Clara County Flood Control and Water Conservation District. Tl~e study recommended numerous improvements to Hale Creek, including lining porti~~ns of the invert with concrete, building a debris basin upstream of Fremont Avenue, and replacing six bridges and culverts. Based on this work, in the early 1960's a concrete-lined trapezoidal channel was constructed on Hate Creek beginning at the confluence with Permanente Creek and extending upstream to Rosita Avenue. This work is detailed in the "Hale Creek Improvement Zone N.W.-1 "Northwest"; Project No. 9, Unit 1" plans dated 19!59 and 1960. Permanente Creek -Bay to Highway 101 In the early 1960's, a trapezoidal channel was constructed on Permanente Creek from Mountain View Slough to Highway 101. Portions of the channel were lined with concrete, but the majority of the channel was unlined. The work is detailed in the 1960 "Permanente Creek Improvements" plans. Permanente Creek Vertical -Walled Concrete Channel In 1961, a soils report entitled "Proposed Improvements of Permanente Creek" was prepared by Cooper & Clark Consulting Engineers for the Sant~~ Clara County Flood Control and Water Conservation District. The study consisted of the ~~nalysis of 9 soil borings from Highway 101 to Mountain View Avenue to determine if the soils wE~re suitable for the construction of a concrete vertical walled channel. In 1962 avertical-walled concrete channel was constructed from EI Camino Real to Hale Creek. The work is detailed in the 1962 "Permanente Creek -Hale Creek to EI Camino Real" plans. In 1967 avertical-walled concrete channel was constructed on Permanente Creek from Highway 101 to Villa Street. The project is detaile~~ in the 1965 plans, "Permanente Creek - Bayshore Highway to Villa St." Permanente Creek -Villa St. Culvert and Califa~rnia/E/ Camino Culvert In the early 1960's, two box culverts were constructed: the Villa St. culvert and the California/EI Camino culvert. A concrete-line trapezoidal channel was constructed between the two culverts. Permanente Creek Flood Protection Project Page 5 Planning Study Report July 2008 The work is detailed in the following plans: "Permanente Creek - EI Camino Real to Latham St", 1962; "Permanente Creek -Villa St. to 485 ft. South of Villa St.", 1963; "Permanente Creek - 485 ft. South of Villa St. to California St.", 1964; and "Permanente Creek, California St. to Latham St., 1964. Mountain View Slough Studies In 1964, the Santa Clara County Flood Control and Water District prepared a "Report on a Study of Drainage of the Mountain View Bay Front Area and Permanente and Stevens Creeks Outfall Channels." The report proposed that a slotted weir be installed to reduce sedimentation in Mountain View slough. The report also studied methods of draining the lowland areas near the Bay in Mountain View; the study concluded that pumping is the most effective method of draining these areas. In 1966 the "Mountain View Slough Slotted Weir Study" was prepared by Lynne Burst for the District. This study concluded that a slotted weir in Mountain View Slough, as proposed in the 1964 study, would not be effective in reducing sedimentation in the slough. The slotted weir was therefore not installed. Mountain View Slough -East Levee Raising In 1976 the Final Environmental Impact Report on the Proposed Mountain View Slough Levee Repair Project was prepared by the Santa Clara Valley Water District. The report studies the environmental impacts of raising the eastern levee of Mountain View Slough. In 1993 the eastern levee of the Mountain View Slough was raised. This work is detailed in the 1993 plans, "Permanente Creek, Mt. View Slough East Levee Raising and Maintenance Access Road". The West levee was not altered. Permanente Creek and Permanente Diversion Planning Study and Improvements The 1979 "Permanente Creek Planning Study, Final Engineer's Report" addressed flooding, erosion, and sedimentation problems on Permanente Creek from Portland Avenue to Hale Creek and along the Permanente Diversion Channel. The plan recommended modifications to the diversion channel and to the creek near Portland Avenue which would provide 25-year protection to that area. The plan also proposed flood-proofing. EI Camino Hospital to provide one-percent flood protection. Construction of reservoirs in the upper portion of the watershed was evaluated but could not be justified due to a low benefit/cost ratio. In 1981 the following work was performed on Permanente Creek: the trapezoidal channel downstream of Portland Avenue was lined with concrete; and sacked concrete was installed in the channel upstream of Cuesta Drive and downstream of Marilyn Drive. In 1981 the following work was also performed on the Permanente Diversion Channel: a 183-centimeter (72-inch) pipe was installed under Blach Jr. High School to supplement the capacity of the existing double box culvert; floodwalls near Carmel Terrace were raised; and the Diversion Channel entrance to the box culvert under Highway 85 was modified. This work was detailed in the 1980 plans "Permanente Diversion and Permanente Creek." In 1981, EI Camino Hospital was flood-proofed to ensure that the hospital was protected against the one-percent flood. Flood-proofing measures included the installation of earth mounds, floodwalls, and ramps. Permanente Creek Flood Protection Project Page 6 Planning Study Report July 2008 Permanente Diversion -Remedial Measures ai` Blach School In 1984 a study entitled "Permanente Diversion Channel Remedial Flood Control Measures (at Altamead Drive and Blach School), Engineer's Report and Negative Declaration", was prepared to address flooding, sediment and maintenance problems on the Permanente Diversion near Altamead Drive. The study proposed removing th~~ existing buried culverts and replacing them with avertical-walled open channel in order to allow for easier sediment removal. The study was prepared in response to the 1983 flooding of Blach Jr. High School and surrounding areas. In 1986 the double box culvert and the 183-centimeter (72-inch) pipe under Blach Jr. High School along the Permanente Diversion Channel were removed and replaced with avertical- walled concrete channel. This work is detailed in the 1985 plans "Permanente Diversion Channel." Study of Proposed Permanente Creek Flood G~ntrol Dam In 1996, a report entitled "Preliminary Geologic Evaluation of Permanente Creek for the Proposed Siting of a Flood Control Dam" was pre~~ared by the District to provide a preliminary reconnaissance evaluation of the geological conditions at a proposed dam site in the upper watershed of Permanente Creek. The study concluded that the proposed dam site may not be feasible due to geologic conditions. The study identified two alternative dam sites where geological conditions were more favorable; however, both of these locations would provide less flood storage. To date, no flood control dam has been constructed in the watershed. 1.7 Previous Studies and Actions by Other Agencies FEMA Floodplain Studies In 1980, the Federal Emergency Management AgE~ncy (FEMA) published Flood Insurance Studies for the Cities of Mountain View and Los Ahtos. The purpose of these studies was to identify the existence and severity of flood hazards within these cities. U.S.G.S. Sediment Studies In 1989, the U.S. Geological Survey published the Water-Resources Investigations Report 89- 4130, "Effects of Limestone Quarrying and Cement-Plant Operations on Runoff and Sediment Yields in the Upper Permanente Creek Basin, Sarrra Clara County, California. The report was prepared in cooperation with the District. The report quantified the impact of the upstream cement and aggregate quarry on creek sedimentation. 1.8 Cities and Major Property Owners Within tree Watershed City of Mountain View The northern portion of the Permanente Creek watershed lies within the City of Mountain View. This section relates portions of the City's General Flan dealing with creek issues, as well as the City's Shoreline at Mountain View Park and a prop~~sed pedestrian trail along Permanente Creek. Permanente Creek Flood Protection Project Page 7 Planning Study Report July 2008 General Plan Environmental Management Polices and Actions from the Mountain View General Plan which may be related to flood management within the Permanente Watershed include the following: • "Protect residents and their property from flood hazards." • "Preserve and enhance the biological resources in Mountain View." • "Promote the visibility of and safe physical access to San Francisco Bay, the baylands, Stevens Creek, and other natural resources in the city." • "Improve open space areas to provide a diversity of recreational and leisure opportunities for the community." Shoreline at Mountain View Shoreline at Mountain View is a regional park and nature preserve owned by the City of Mountain View which encompasses 2.52 square kilometers (622 acres). Shoreline at Mountain View is located at the extreme northern end of the City of Mountain View, and is bounded by Amphitheater Parkway to the south and salt ponds to the north. Permanente Creek runs south to north through the center of the park. The park contains approximately .96 square kilometer (237 acres) of wetland habitat, 0.78 square kilometer (195 acres) of upland habitat, a 0.81 square kilometer (200 acre) golf course, and a sailing lake. The Mountain View Tidal Marsh is located on the east side of the main channel of Permanente Creek, just upstream of the salt ponds. The Mountain View Tidal Marsh is a part of Mountain View Slough, and is connected to the main channel of Permanente Creek. Shoreline Lake is a small salt-water lake used primarily for windsurfing. The lake is maintained by pumping water into the lake from the Bay, and discharging the overflow into Permanente Creek at an outfall near Shoreline Boulevard. Prior to the development of Shoreline at Mountain View, a sanitary landfill was created on site. The landfill served the dual purpose of raising money to fund the park, and raising the elevation of the site to reduce the risk of flooding. The large hill (Vista Slope) located on the eastern side of Permanente Creek immediately north of Amphitheater Parkway marks the remains of the inactive landfill. Shoreline Amphitheater, a large outdoor concert venue, is located adjacent to the Vista Slope and Shoreline at Mountain View. Proposed Permanente Creek Pedestrian Trail The "City of Mountain View Permanente Creek Development Guidelines" (1996) describes plans fora 1.6 kilometer pedestrian and bicycle trail along the east side of Permanente Creek between Highway 101 and Shoreline Boulevard. Portions of the proposed trail are located within lands held through fee title or easement by the District. Permanente Creek Flood Protection Project Page 8 Planning Study Report July 2008 City of Los Altos The central portion of the Permanente watershed lies within the City of Los Altos. This section relates portions of the City's General Plan dealing with creeks issues. • "Reduce the potential for flooding along the creeks that traverse Los Altos." • "... continue to discourage concrete lining of creek beds and encourage Santa Clara Valley Water District to use environmentally sensitive solutions to control local erosion problems. • ... encourage the Santa Clara Valley WatE~r District to regularly maintain creek banks, to clear drainage channels of silt and debris, and to minimize disruption to riparian habitat in an environmentally sensitive manner." • "Minimize the risk of hazards to Los Altos residents." • "Preserve and protect natural areas -natural creek channels, topography, and vegetation -which are valuable natural re:~ources." • "Preserve the natural beauty and rural-suburban atmosphere and the high quality of residential neighborhoods in Los Altos." County of Santa Clara The southern (upstream) portion of the Permanente watershed lies within the County of Santa Clara (County). This section relates portions of the County's General Plan dealing with creek issues. • "Restore wetlands, riparian areas, and other habitats that improve Bay water quality." • "Improve current knowledge and awarene:~s of habitats and natural areas." • "Protect the biological integrity of critical h~~bitat areas." • "Encourage habitat restoration." • "Develop parks and public open space lanes." • "Minimize the resident population within hilah hazard areas. • "Reduce the magnitude of the hazard, if feasible." • "Reduce non-point source pollution." • "Prepare and implement comprehensive watershed management plans." Rancho San Antonio County Park and Rancho San Antonio Open Space Preserve Rancho San Antonio County Park is located in they foothills southwest of Highway 280 and immediately north of the Hanson Cement Plant and limestone quarry. The park is located within Permanente Creek Flood Protection Project Page 9 Planning Study Report July 2008 the Permanente watershed. Permanente Creek runs through the center of the park. The 0.7 square kilometer (165 acre) park is mostly undeveloped and contains several hiking, biking, and equestrian trails. Most of the park's development is located along the eastern side of the park; developments include parking lots, picnic areas, tennis, handball and basketball courts and playing fields. The park is owned by the County but operated by the Mid-Peninsula Regional Open Space District (MPROSD) Rancho San Antonio Open Space Preserve, which is owned and operated by MPROSD, is located in the foothills southwest of Highway 280, immediately west of Rancho San Antonio County Park. The majority of the park's 8.6 square kilometers (2,135 acres) of open space lie within the Permanente Watershed, and most of South Branch Permanente Creek and North Branch Permanente Creek are located within the Preserve. Development within the park includes the Deer Hollow Farm, an interpretive farm which is open to the public, and 37 km (23 miles) of hiking and equestrian trails. Hanson Cement Plant and Limestone Quarry The Hanson (formerly Kaiser) Cement Plant and Limestone Quarry is located in the upper Permanente Creek Basin. The limestone mined from the quarry is used for the on site production of cement. The quarry and cement plant operations directly affect over 1.2 square kilometers (300 acres) of the upper Permanente Creek Basin. Minor quarry operations began in 1900; operations increased in 1939, when large amounts of cement were produced for Shasta Dam. Operations have continued at large scale up to the present time. Based on discussions with plant management, plant operations will continue into the foreseeable future. Cargill Salt Ponds/ Federal Wetlands Restoration Area Salt evaporation ponds formerly owned by Cargill Incorporated (formerly Leslie Salt Co.) and now owned by the United States covering a total area of over 3.2 square kilometers (800 acres), are located adjacent to both sides of Reach P1 of Permanente Creek (along Mountain View Slough). The salt ponds are bound to the north by San Francisco Bay, and to the south by Shoreline at Mountain View. These two ponds are the first two in the salt-making chain that ringed the South Bay; therefore, they are the least saline of the salt ponds. Both the east and west creek levees were owned by Cargill. The District had an agreement with Cargill to maintain the east levee at an elevation of 9.5 feet above mean sea level; the District has no responsibility to maintain the west levee. The ponds have been purchased by the U.S. Fish and Wildlife Service for the South Bay Salt Pond Restoration Project, which is a long-term planning effort underway to determine the restoration plan for the ponds. The current preliminary plan is to restore the ponds back to their natural salt marsh habitat, although schedules and means have not yet been determined. 1.9 The Recommended Capital Improvement Project After evaluating a thorough range of alternatives, including several alternatives that met the project objectives and the District Board's Ends Policies and the No Project alternative, this report recommends a capital improvement project to be constructed. The recommended project would improve flood protection for the citizens of Mountain View and Los Altos, would improve flood protection for local streets and utilities, would address the long term deterioration of the previously built concrete channels, and would provide opportunities for environmental Permanente Creek Flood Protection Project Page 10 Planning Study Report July 2008 enhancements and trail construction. The recommended project would provide Natural Flood Protection by doing the best possible job of balancing the various flood protection objectives. A summary of the recommended alternative`s project elements, costs, and benefits is provided below. The project would be funded by Clean, Safe Creeks funds, with construction scheduled for 2010 to 2016. The project elements would be designed and built in phases, with emphasis placed on whichever elements are capable of being designed more rapidly in order to provide the fastest flood protection. The recommended project would include the following elements: Offstream flood detention facilities in: o Rancho San Antonio Park o Blach Jr. High School o Cuesta Park Annex o McKelvey Park • Bypass channel for Reach H2 of Hale Creek. • Bypass channel for Reach P7 of Permanente Creek. • Channel widening for Reaches P5 of Permanente Creek and H1 of Hale Creek. • Floodwalls north of Highway 101 to downstream of Amphitheater Parkway. • New low-flow diversion structure at the Permanente Diversion. • Opportunity for riparian restoration and public trail extension in Reach P3 between Highway 101 and Middlefield Road. Permanente Creek Flood Protection Project Page 11 Planning Study Report July 2008 ~ i = Permanente Creek ~ j ~ Planning Study ~~.,. ,~~ Pemanente Creek ]"-~~ Flood Plain poi Pemanente Creek 1~1'atershed Boundary Parcels in Flooii Plain: 3170 `%, <., 11lountain View: ?740 ~~ /J'ti,, Los alms: 430 ,, r ~ Ik '~ / '/7 _ 1 \ ;1I~wi1Jm l wM i J ' ~ J 1`_ Z // /7 'f/t// • lF~7A DR Y Z J __ \ ~.._ 1'(JL1i~\L\!L ~~ ~~l~,.~ rr.Finn~>r.~ -_-, i H-1V'1~f! Figure 1.1. Permanente Watershed & Floodplain Permanente Creek Flood Protection Project Page 12 Planning Study Report July 2008 P 4 - i -c., `.~ :'~ ~~ -..c , ~~'<` :,, ~ ~ ` ,~ ~ ~~ t FRS[O \ J kN - -. . /~/ HALE CREEK & )IVERSION 4AP Figure 1.2. Reach Map Permanente Creek Flood Protection Project Planning Study Report Page 13 July 2008 Permanente Creek Flood Protection Project Page 14 Planning Study Report July 2008 CHAPTER 2 WATERSHED DESCRIPTION This chapter provides a description of the Permanente Creek watershed. Information on the basin hydrology, geology, and setting is provided in the following sections. 2.1 Watershed Description The Permanente watershed lies within the Northwest portion of Santa Clara County and is in the District's Lower Peninsula Flood Control Zone. The lower portions of the watershed lie within the cities of Mountain View and Los Altos, while the upper watershed is located in an unincorporated area of Santa Clara County (see Figure 1.1 -Watershed Map). Water flows from the Santa Cruz Mountains in the South to the floor of the Santa Clara Valley and the San Francisco Bay in the North. Permanente Creek forms in the upper watershed area at the confluence of North Branch (Ohlone Creek) and South Branch Permanente Creeks. The major tributary to Permanente Creek is Hale Creek, which connect to Permanente Creek just south of EI Camino Real. Tributaries to Hale Creek include Magdalena Creek, Loyola Creek and Summerhill Channel. The majority of the flows from the upper Permanente watershed area are diverted to Stevens Creek through the Permanente Diversion Channel. Hale Creek has a watershed area of approximately 10.4 square kilometers (4 square miles); while the Permanente Creek watershed area is approximately 45.3 square kilometers (17.5 square miles) at its outflow to San Francisco Bay. The Permanente Creek watershed has asemi-arid Mediterranean climate characterized by mild, wet winters, and warm, dry summers. The distribution of rainfall is strongly affected by topography. Rainfall levels are highest in the upper watershed area in the Santa Cruz Mountains and lowest by San Francisco Bay. Average annual rainfall ranges up to 91 centimeters (36 inches) per year in the highest sections of the hills, while the average annual rainfall near the Bay is only 33 centimeters (13 inches). Over 80 percent of the seasonal precipitation occurs between November and March. The steep topography of the upper watershed results in short duration, high intensity runoff during major storms. Runoff in the lower, urbanized section of the creeks is conveyed to the creeks by the municipal storm drain system, which tends to increase the magnitude of the more frequent events, while partially reducing the magnitude of very large events. 2.2 Creek Descriptions This section presents brief descriptions of the reaches of Permanente Creek, Hale Creek, the Permanente Diversion, and Stevens Creek in the study area. Permanente Creek is described between San Francisco Bay and Foothill Expressway, Hale Creek is described from its confluence with Permanente to Foothill Expressway, and the Permanente Diversion Channel is described in its entirety. Permanente Creek Flood Protection Project Page 15 Planning Study Report July 2008 2.2.1 Permanente Creek 2.2. i.1 Reach P1: San Francisco Bay to Boat Pond Bridge This reach is an earth levee channel with tidal marsh vegetation. For the most part, the reach is a wide channel with a low flow (tidal) channel meandering through it. Salt ponds are located on both sides of the creek. It is difficult to gain access along this reach since there are no access points into the channel, and the maintenance pedestrian road further upstream on the west bank stops at the upstream end of the salt ponds. ~:-. ~ws, _, c~~s w~ ~ +R" ~ - , Aa ~ , _ ~ . ~k^ "" ir. ' ' "' ._ ~ .~ u ~ ~ ~ ~K j x ~ ~ '+ ~~r I ~ ~~~*~ , b j ~ Vy _ a ~ ~ r , { . ~ .~. f f Figure 2.1. Typical Photo of Reach P1 2.2.1.2 Reach P2: Boat Pond Bridge to Highway 101 This reach contains an earthen levee channel with tidal and brackish marsh vegetation in the lower banks and scattered ornamental and upland trees on the upper banks. From the salt ponds to Amphitheatre Parkway, the reach has a wide invert with a meandering low flow channel. From Amphitheatre Parkway to Highway 101, the channel is trapezoidal earth with levees. There are no access points into the channel but there are maintenance roads on both banks along most of the reach. Permanente Creek Flood Protection Project Fage 16 Planning Study Report July 2008 as ' Y7[~ .~Y .~ s l ~~ ~~ ~ 4 ~ r ~y~, ~~~ ~ . ~ . ~" ,, .: u4. ~ .~ '°6 'Y ~~.a.^~,.... j ~ R~ Figure 2.2. Typical Photo of Downstream Portions of Reach P2 Figure 2.3. Typical Photo of Upstream Portions of Reach P2 Permanente Creek Flood Protection Project Page 17 Planning Study Report July 2008 2.2.1.3 Reach P3: Highway 101 to Villa Street On the downstream side of Highway 101, for 58m the reach is a concrete trapezoidal channel. From Highway 101 upstream to Villa Street, the channel is rectangular concrete (U-Frame). The channel dimensions (w x h) from Highway 101 to Central Expressway are 3.66m x 2.74m (12 ft x 9 ft). The channel dimensions from Central Expressway to Villa Street are 3.048m x 3.048-3.5m (10 ft x 10-11.5 ft). There are maintenance ramps leading into the creek on the downstream sides of the Rock Street, San Luis Avenue, Hackett Avenue, and Villa Street culverts. There is a 0.56m (1.8 ft) drop structure about 10 meters downstream of the Hetch-Hetchy Bridge. 2.2.1.4 Reach P4: Villa Street to E/ Camino Real The reach consists of two underground culverts separated by a 54m long concrete trapezoidal section. The Villa Street culvert is about 270 meters long and extends from the downstream end of Villa Street to about 55 meters downstream of California Street. The EI Camino/California culvert is about 795 meters long and extends from the downstream end of California Street to about 60 meters upstream of EI Camino Real. There is a maintenance ramp on the downstream side of Villa Street. There are two drop structures along this reach. One is located at the downstream end of the EI Camino/California culvert; the other is located within the same culvert underneath Latham Street. Permanente Creek Flood Protection Project Page 18 Planning Study Report July 2008 Figure 2.4. Typical Photo of Reach P3 2.2.1.5 Reach P5: E/ Camino Real to Confluence with Hale Creek The majority of the channel is a concrete U-Frame with w x h dimensions of 3.66m x 2.13- 3.048m (12 ft x 7-10 ft). At the Hale Creek confluence, the channel changes to a concrete trapezoid. There is a maintenance ramp at the downstream end of the Mountain View Bridge. There are two sloped drops along this reach, one just upstream of the EI Camino Real culvert and another just upstream of the Park Avenue bridge. Figure 2.6. Typical Photo of Reach P5 Permanente Creek Flood Protection Project Page 19 Planning Study Report July 2008 Figure 2.5. Typical Photo of Reach P4 Between the Culverts 2.2.1.6 Reach P6: Confluence with Hale Creek to Miramonfe/Cuesta Culvert This reach is a natural earth channel and typically quite small, with some sections of sacked concrete (SCSP), shotcrete, and stacked concrete walls. The vegetation varies from mature trees and grass to no vegetation at all (bare earth). It is difficult to access this reach, but there are access gates (no ramps) at Barbara Avenue, Marilyn Drive, and the Hale Creek Confluence. 2.2.1.7 Reach P7: Miramonte/Cuesta Culvert to Permanente Diversion This reach consists of a natural, trapezoidal-shaped channel with some steep banks. The vegetation consists mainly of mature trees with little or no undergrowth. There are no maintenance ramps to gain access to the creek along this reach. There is a gate at the Covington Bridge for access to the old stream gage at that location. There is one main vertical drop just downstream of Abandoned Bridge #31. Figure 2.8. Typical Photo Along Reach P7 Permanente Creek Flood Protection Project Page 20 Planning Study Report July 2008 Figure 2.7. Typical Photo Along Reach P6 2.2.1.8 Reach P8: Permanente Diversion to Foothill Expressway This reach consists of a concrete trapezoidal section about 340 meters long upstream to Portland Avenue, followed by a large natural channel from Portland Avenue to Foothill Expressway. There are two maintenance ramps downstream of Portland Avenue. There are also two drop structures downstream of the Portland Avenue bridge, one of which is part of the Permanente Creek stream gage. < 7, «~., ~.~..y. s~~ ~®Y_' ', ~~! i- •~ ~ i „a~F~v~ d' ~ ~r , j ~~• rya .. ~ - ~ I ,_ ~. ff<; rs ~h; Figure 2.9. Typical Photo for Reach P8 Downstream of Portland Avenue ~~ , ~ r - - - - y~~ ai 1 _ :~ ! t. ' _ ~ -ram- ' `~''v-_` ~ ~~* t r a ~r,;.. `~~ '_` r,' yL_ ~ S~ "'mac ~ ~ tj ' ~ J ~ f r ~ J ~ ~ _ l " r x.. ,-~ _ 1. y .^: ~ ~* ~ . ~ x tf9 Y c. r .K.< 0 ~. ^S~ 1 i ' 1 Sk r _ t. Y YJ r ' ~_ ~ ~ .A ~{ ~r ~ s : ~'f' l _ ~ _ Figure 2.10. Typical Photo for Reach P8 Upstream of Portland Avenue Permanente Creek Flood Protection Project Page 21 Planning Study Report July 2008 2.2.2 HALE CREEK 2.2.2.1 Reach H1: Confluence with Permanente Creek to Rose/Rosita Culvert In this reach, the channel consists of a concrete channel which varies from straight to mildly sinuous sections. All sections are either U-frame or trapezoidal. All bridge crossings are freespans, with some private crossings composed of steel and wooden sections. 2.2.2.2 Reach H2: Rose/Rosita Culvert to Foothill Expressway The channel alignment varies from straight to mildly sinuous. The channel is natural with a simple trapezoidal configuration. Both banks are well-vegetated, with mature riparian trees and varying levels of undergrowth. Channel bottom sediments consist of sand and gravel. Figure 2.12. Typical Photo of Reach H2 Permanente Creek Flood Protection Project Page 22 Planning Study Report July 2008 Figure 2.11. Typical photo of Reach H1 2.2.3. Permanente Diversion 2.2.3.1 Reach PD: Confluence with Steven Creek to Permanente Creek The channel is mostly a concrete trapezoid with minimal to no sediment. There is a portion of the channel along Blach Junior High School (upstream of Grant Road) that is a larger concrete U-frame with heavy amounts of gravel and sand deposition. Figure 2.13. Typical Photo of Reach PD (trapezoidal section) f v Figure 2.14. Typical Photo of Reach PD (U-Frame section) Permanente Creek Flood Protection Project Planning Study Report Page 23 July 2008 2.3 Watershed Hydrology Appendix I contains the hydrology report, which was prepared by District Hydrology Unit staff. The report provides detailed information on the hydrology methodology and design flow calculations. Table 2.1 shows the design flow values for the watershed: Table 2.1 -Watershed Design Flow Values Drainage Design Design Location Area (km2) 1 % Flow 10% Flow (cros) (cros) South-branch Permanente 4.0 48 27 North-branch Permanente Creek 3.5 25 11 Ohlone Permanente upstream of Hwy 280 7.5 71 40 Permanente upstream of Diversion 8.4 76 42 Permanente Diversion - 40 31 Permanente upstream of Hale Creek - 40 14 Hale Creek upstream of Permanente 4.4 31 19 Permanente downstream of Hale 14 0 65 27 Creek . Permanente @ SPRR 15.8 71 31 Permanente @ Hwy 101 16.5 74 34 Stevens Creek downstream of 24.9 218 127 Diversion Stevens Creek @ EI Camino Real 26.5 221 130 Stevens Creek @ Hwy 101 29.8 229 139 2.4 Watershed Physiography and Geology The Permanente Creek watershed is one of several relatively moderate-sized drainages on the eastern slopes of the Santa Cruz Mountains and floor area of Santa Clara Valley in the northwestern portion of the county. It lies between the Stevens Creek drainage on the south and east and Adobe Creek drainage on the west. The headwaters originate near Black Mountain, approximately 850 meters (2,800 feet) above sea level, along Monte Bello Ridge. The main drainage flows southeasterly through the mountains and shifts to the north at the foothills. At an elevation of approximately 90 meters (300 feet), it emerges from the foothills into Santa Clara Valley, passing across the valley floor. Stream flows are ephemeral. Permanente Creek continues to flow north across the valley floor to San Francisco Bay. It is joined by Hale Creek, its principle tributary from the west, just south of EI Camino Real. The headwaters of Hale Creek are in the foothills area within the Town of Los Altos Hills. Within the valley floor area both streams pass through the cities of Los Altos and Mountain View. The natural drainage system has been altered for many reasons, including alterations to accommodate greater flood protection. These include (1) a cutting of a high water diversion channel within the valley floor eastward to Stevens Creek from a point above the confluence of Permanente Creek Flood Protection Project Page 24 Planning Study Report July 2008 Hale Creek and (2) the diverting of the mouth of the stream into San Francisco Bay from Charleston Slough eastward to Mountain View Slough. Stevens Creek, which originally entered the Bay at Mountain View Slough, was diverted eastward to form its new mouth at Whisman Slough. Monte Bello Ridge, and most of the mountainous portion of the drainage, is underlain by the Franciscan Group of formations, a regional unit that forms much of the core of the Coast Ranges of California. The Franciscan Group consists of highly deformed, contorted, faulted, sheared and weathered sections of shale, sandstone, chert, limestone, and greenstone (metavolcanic rock). These were deposits as ancient sea floor sediments in a subduction zone where continental and oceanic plates were colliding on the crust of the earth. The colliding action, like sediments carried on converging conveyor belts, accounts for the intense deformation of the units. These were pervasively intruded by serpentine which is generally intensely sheared. The lower portion of the mountainous area is underlain by a narrow strip of northwesterly bedded tertiary shale of the Monterey Formation. These were deposited in inland seaways which invaded portions of the continent's edge during the Tertiary period (2 million to 65 million years ago). The foothills are underlain by gently and broadly folded claystone, sandstone, and conglomerate of the Santa Clara Formation. These are lightly consolidated to compacted and were deposited as alluvial outwash from the uplifting coast ranges during the Plio-Pleistocene epoch (10,000 years to 2 million years ago). The older formations in the mountainous areas are cut by numerous ancient faults which are inactive. The closest active fault is the San Andreas fault which passes west of the watershed through the northwesterly trending Stevens Creek Canyon, just over the ridgeline of Monte Bello Ridge. The possibly active, northwesterly trending Monte Vista fault passes through the foothills of the watershed, forming a fault contact between the Franciscan Group on the southwest and the Monterey Formation on the northeast. This fault may be the northwesterly extension of the possibly active Shannon fault. The valley floor area is underlain by young, unconsolidated alluvial fill washed down from the Santa Cruz Mountains. The upper elevated edge of the valley floor is underlain by alluvial fans, which splayed out from the mouths of streams emerging from the foothills and which have laterally coalesced with adjacent fans and contain relatively coarse sediments. Descending down the fan to its distal portion and onto the flat baylands, the surficial sediments become finer. They were deposited as basin, shallow marine and tidal deposits. The aggregation of unconsolidated sedimentary section beneath the valley floor, and including the subsurface portion of the Santa Clara formation beneath the young alluvial deposits, constitute the Santa Clara Valley groundwater basin. The maximum depth of the basin is in excess of 457 meters (1,500 feet). Groundwater in the basin may be unconfined (water table) or confined (under pressure). The pressure zone includes the deep aquifers within the basin areal interior. The mineral quality of waters draining the mountainous and foothills area is expected to be a calcium bicarbonate to acalcium-magnesium bicarbonate type, ranging in total dissolved solids from about 150 to 350 milligrams per liter. Water of this concentration is suitable for most beneficial uses. The higher range of total dissolved solids concentration occurs at low flows when such flows are sustained by groundwater discharges from the bedrock and Santa Clara Formation. As the flows enter the valley, a certain amount infiltrates into the valley fill as natural ground water recharge. Beneficial recharge occurs in the elevated edges of the valley where the groundwater is unconfined and beyond the subsurface edges of the confined area. This area is known as the forebay of the basin. Along Permanente and Hale Creeks, the forebay extends from the foothills line to their confluence. Descending down the fan toward the Permanente Creek Flood Protection Project Page 25 Planning Study Report July 2008 baylands, the stream gradient flattens and the depth to groundwater beneath the stream is very shallow. Due to land subsidence, which created a local inland hydraulic gradient from the Bay, tidal water flows farther upstream across the subsided zone. This intrusion has caused the shallow aquifers beneath the bayfront area to become contaminated by salt. Land use within the drainage varies. Large areas of the mountainous watershed are part of a limestone quarrying and Portland cement manufacturing operation. A portion below the cement operation is used for aluminum and chemical plant operation. Ranching is limited. Parts of the foothill areas are open lands with scattered oak trees and grassy slopes and a limited amount of dry farming and other parts contain residential development. The watershed within the valley floor is covered by urban development except for a portion of the baylands which is covered by salt evaporation ponds adjacent to the Bay and by a municipal landfill in the baylands that has been landscaped for recreational use. Urban development consists of residential use in elevated portions of the valley floor, commercial and residential use toward the toe of the fan, and industrial use at the upper edges of the baylands. 2.5 Historical Stream Channel Permanente Creek has been significantly changed by human activity. Some of these alterations in creek geomorphology are very old. The oldest maps available show quite a different watershed than the one existing today. For example, the 1862 Railroad map (see Figure 2.15) and the 1872 City of San Jose map (see Figure 2.16) show that Permanente Creek used to naturally be a tributary to Stevens Creek (called "Cupertino Creek" in the former map and "Stephens Creek" in the latter map. As with most of the west-side creeks, Permanente/Stevens did not have a channelized path to the Bay but would simply drain to the marshes and disappear into various small sloughs. By the time the 1876 Thomas Thompson & West Historical Atlas of Santa Clara County was published, the situation had been radically altered. Both Stevens Creek and Permanente Creek had already been separated, straightened, and channelized to the Bay. An obviously straightened man-made channel had already been constructed downstream of the Southern Pacific Railroad tracks to carry flows from Permanente Creek into Charleston Slough. The 1899 (reprinted in 1923) USGS. Topographic Palo Alto Quadrangle shows that the alignment of Permanente and Hale Creeks upstream of Fremont Avenue is very similar to the present day alignment. Between Fremont Avenue and EI Camino Real, Permanente Creek followed the present day alignment with the exception of an area near Cuesta Drive where the original channel has natural meanders while the present day channel was straightened to align with Miramonte Drive. The 1948 USGS Topographic Palo Alto Quadrangle shows that Permanente Creek was re-aligned downstream of the railroad tracks so that the creek closely follows its present-day alignment and discharges into Mountain View Slough. This map also shows Hale Creek terminating upstream of Springer Road. Thus, by the early 1940's, the creeks were generally in their current alignment. Permanente Creek Flood Protection Project Page 26 Planning Study Report July 2008 .,., ~ I ~~\ / ~ /~ t = ~ i ;, l// ~ I, ~ / I ~ ~ ~i: ~ _ _ ~,. _ • . i 'yc,; 'i ~ a .~~* .- :~ s x~« Mr~.a , QCLlf ~ Figure 2.15. San Francisco San Jose Railroad, Allardt, 1862 ~ngfa •,-~ 0! ' f ~~ /'/~~~~~ \ 1. ~/ G r `. . ~ G Permanente Creek Flood Protection Project Page 27 Planning Study Report July 2008 2.6 Land Subsidence Over-drafting of the groundwater basin has caused land subsidence over the confined interior portion of the basin. Over-drafting refers to the process of extracting more water out of underground aquifers through pumping than is being replaced through percolation. The compressible layers of soil come under increased pressure as water pressure drops, causing the soil layers to reduce in width, which causes the general ground surface to drop. Land subsidence is a broad, gradual sagging of the surface that is usually hardly perceptible, except when it involves large hydraulic features such as creeks and pipelines. Subsidence in Santa Clara Valley began in the 1920's and generally ceased in 1969 when over-drafting was eliminated through the importation of water from the State Water Project. Subsidence has led to collapse of well casings, and has had a significant impact on systems that rely on hydraulic gravity flow, such as sewer lines, storm drains, and creeks. Subsidence has caused bayfront lands in Santa Clara County to sink below sea level, enabling salt water to intrude upstream and dramatically affecting the riparian habitat. In addition, subsidence has increased the potential for tidal flooding. Along Permanente Creek the greatest amount of subsidence was about 1.8 meters (6 feet), and was centered approximately where Highway 101 crosses the creek (see 2.17 -Subsidence). The bayfront was depressed below sea level by a few feet. In order to protect the baylands from encroaching bay water over the subsided areas, a bayfront levee system had to be constructed. Stream channels flowing to the Bay had to have their levees raised in order to pass the flows through the subsided areas. Drainage waters accumulating behind the levees had to be pumped over the levees into the channels. The subtle alterations of the topography caused by land subsidence would also have the consequences of a net reduction of the natural flood flow carrying capacity of the stream channels in the downstream reaches. 2.7 Summary of Environmental Setting 2.7.1 Land Use Existing residential, commercial, and industrial development reaches of Hale and Permanente Creeks may restrict or preclude the development of flood management improvements (e.g., channel widening, detention basins) in the urbanized portions of the project area. Where undeveloped, no specific land use constraint is identified apart from the costs of acquisition, which may pose an economic constraint due to the local price of land. The project area includes a diverse array of land uses, mostly residential, commercial, and industrial, with other uses (public, open space, recreational, and agricultural) occurring in some areas. Former agricultural uses, such as orchards, greenhouses, and packing plants were historically prevalent in much of the area. Restoration of riparian habitat in the urbanized areas of the watershed may reduce flood conveyance capacity and increase the frequency of flooding of adjacent properties, which is a constraint for any restoration component of the project. Permanente Creek Flood Protection Project Page 29 Planning Study Report July 2008 Lines of Equal Subsidence _____-_- Santa Clara Valley %~ 3 ~~~`~" ~-~ North County F~ ~'`'~ _ ) `\ 1934-1967 \ Fla Ic A Ito ,t -~:-~'C. ' - ~ • m ~ ~ V ~ 5 _--cam ~ ~ ~ ~ ` ' ~ ~.% Sonto doro Vol~y Water Dkkrkt ~ ~ ` ,^~ \\ ~~ t ^""Z\ Sunnyvale ~~ . ~~,' \ ~ 1 i Lo5 Aftds Hills \\ ~ \ ~~ ~ 1~, 1 ~! ~ ~ ~~~~\ n~ ,~ ~. Capertmo ~~ ~ ~ ~ ~' ' ~ 1 ~J ~ ~ ?- ~~ ~ Figure 2.17. Subsidence in Santa Clara County 2.7.2 Biological Resources A number of special-status plant and animal species have been recorded, or have the potential to occur in the project area. These species include California red-legged frog, California tiger salamander, California clapper rail, salt marsh harvest mouse, western burrowing owl, and western leatherwood. Additionally, species covered under the Migratory Bird Treaty Act likely use habitats within the project area for roosting, nesting, and foraging. Occurrences of these species within the project area may restrict or preclude the development of flood management improvements within specific locations. Approximately 28 acres of jurisdictional wetlands and other waters of the U.S. (Section 404 of the Clean Water Act) have been identified within the project area (south of Foothill Expressway). Construction of flood management improvement facilities in these areas may result in the loss of wetlands and other waters of the U.S. Permanente Creek Flood Protection Project Page 30 Planning Study Report July 2008 2.7.3 Cultural Resources Records searches conducted for the project area and other data collection efforts identified three known cultural resource sites in the upper portion of the project area (south of Highway 280). Additional unrecorded sites may also be present in this location as it is believed that Native Americans inhabited the area prior to Spanish colonization. Construction activities may result in the disturbance and/or degradation of subsurface archaeological resources. Infrastructure (e.g., bridges, conveyance channels) and buildings found within the project area may be subject to NRHP or CRHR, depending upon age and context, for listing as historic structures. 2.7.4 Water Quality A level 1 hazardous materials investigation was conducted in April 2002 (see Level 1 Hazardous Materials Investigation by Dames and Moore (D&M) Consulting Engineers 2002). This investigation provided the following information. For the portion of the watershed north of Middlefield Road, groundwater and surface water has been widely affected by regional volatile organic compound plumes likely associated with historic industrial uses. Soils and groundwater have also been affected by lawn care chemicals, polynuclear aromatic hydrocarbons and metals associated with the former Palo Alto sewage treatment plant, and gasoline and hydrocarbon spills and runoff mainly associated with former gas stations, dry cleaning, and painting businesses in the areas well as the Jones Hall US Army Reserve Center. Soil impacts from pesticides are mostly concentrated in the portion of the watershed between Middlefield Road and Foothill Expressway, where the main agricultural concerns were historically located. The investigation identified potential impacts associated with possible historic spills at former greenhouse and packing plant locations. D&M's report identified nine sites located adjacent to Permanente Creek as sites of potential concern. There were no sites identified along Hale Creek. A level 1 hazardous materials investigation will be conducted for all of the affected areas in the proposed project. It will include physical investigations and site-specific historical research at McKelvey Park, Cuesta Park, Blach School, and the portion of Rancho San Antonio affected by the project. A level 2 investigation will be conducted for the sites affected by the project prior to project construction if the level 1 investigation warrants that effort. 2.7.5 Public Utilities The project has attempted to minimize interference and impacts on local public utilities. Permanente Creek Flood Protection Project Page 31 Planning Study Report July 2008 Permanente Creek Flood Protection Project Page 32 Planning Study Report July 2008 CHAPTER 3 PROBLEM DEFINITION This chapter describes the currently identified problems in the watershed area. 3.1 Creek Flooding 3.1.1 Historic and Recent Flooding The Permanente watershed has a history of recurring floods which have adversely impacted the safety and economic stability of the residents and businesses within the floodplain. Flooding within the Permanente watershed has been documented as far back as 1868. Flooding which has occurred on Permanente Creek, Hale Creek, and Permanente Diversion is described below. Figure 3.1 shows a map of the most recent flooding areas. Permanente Watershed - 1862. A flood of great magnitude occurred in 1862. Records of the flood are poor; however, it is reported that the flood of 1862 was larger in magnitude than the flood of December 1955. Permanente Watershed -January 1911. A large flood occurred in the watershed in January, 1911. Mr. R.E. Nordyke, a resident of the Hale Creek area, reported that "water flowed down Springer Road like a river". The January 20, 1911 Mountain View Register-Leader reported that "Saturday, January 14, 1911 goes down into history as a record breaking day for rainfall in Mountain View. The actual rainfall for that date was 4.60 inches, the greatest recorded in the history of Mountain View." (FEMA, 1980). Flood records are once again poor; however, it is reported that the flood of 1911 was larger in magnitude than the flood of December 1955. Permanente Creek -February 1940. Several homes and some agricultural land in the vicinity of EI Camino Real and Mountain View Avenue suffered light damage. Highways were also damaged and motorists were inconvenienced by the flooding. Permanente Creek -November 1950. November flooding along Permanente Creek caused significant damage to agricultural and commercial properties. The following report ran in the November 20, 1950 Mountain View Register-Leader. "Swollen by the heaviest rains in 32 years, Permanente Creek burst its banks ...and sent torrents of muddy water rushing into Mountain View streets, causing thousands of dollars of damage to merchandise in EI Camino stores... Countless other thousands of dollars of damage was done to orchard land along Miramonte Road by the swirling waters as tons of precious top soil were swept away in the flood" (FEMA, 1980). Permanente Creek -January 1952. Flooding along Permanente Creek caused significant damage to properties in Los Altos and Mountain View. The January 14, 1952 Mountain View Register-Leader reported that "Mountain View's new sewage plant was nearly under water, the EI Camino Real underpass to Highway School was cut off to traffic, six homes on Springer Road were isolated, an office on EI Camino and a house on Grant Road were inundated, ...and navy pump crews prevented lapping waters from flowing into buildings at Moffet Homes" (FEMA, 1980). Flooding also occurred near San Ramon Avenue, San Luis Avenue, Middlefield Road., and at the intersection of EI Camino Real and EI Monte Avenue. Permanente Creek Flood Protection Project Page 33 Planning Study Report July 2008 :~ . 's~. Feb uary 1998 f ,. ~. hay ~. ~. YW: { ~ _ J ~ ~~ Jancrary 1995 & ~© February 1998 f February 1998 I February 1998 February 1998 anuary 1995 & February 1998 ~{;y+yE~~~ i _MwwEa ----~>-~ ~ - March 1983 v ;, Permanandte Creek Legend /'~ E Hdle Creek ' ~"+` Recent) Flooding 1% flood Limits & 1°~6 Flood Limits ° Recent Flooding (700 Year Frequency) 0 0.5 1 Mlles Figure 3.1. Recent Flooding Permanente Creek Flood Protection Project Page 34 Planning Study Report July 2008 Permanente Creek and Hale Creek- December 1955. One of the greatest storms in modern times in Santa Clara County occurred in December 1955, the so-called "Christmas Storm." Most of the flooding occurred in the lower reaches of Permanente Creek where approximately 770 acres were inundated with floodwaters. Flooding near EI Camino Real and Highway 101 was reported. During the flood, downed trees and debris blocked culverts and caused the creek to overtop its banks. Residential homes, agriculture, and commercial business in Mountain View and Los Altos sustained losses. Salt ponds at Mountain View Slough suffered extensive losses due to the flow of fresh water into the ponds. Several bridges and culverts in Mountain View were extensively damaged and eroded. Approximately 100 people residing in lowland areas were evacuated from their homes for a period of two weeks as a result of the flooding. The Mountain View Register-Leader reported that Police, Fire, and City crews were called on " to battle swollen Permanente Creek and flooded streets fed by rains which poured into the area without letting up" (FEMA, 1980). At Hale Creek, water overtopped the creek's banks near Marilyn Dr., Rosita Ave., Covington Drive, and Mountain View Avenue. Flooding in this area was reported to be up to 1 foot deep. Significant flooding is also reported to have occurred in the upstream portion of the watershed, in the vicinity of Magdalena Avenue and Hillview Road. Damages in the Permanente watershed totaled at $142,500 in 1955 dollars. Permanente Creek -April 1958. In 1958, flooding occurred along both the upper and lower reaches of Permanente Creek. Flooding in the upper reaches was confined to areas near the creek. Water overtopped the banks at several locations and flooded streets, sidewalks, and yards in Los Altos and Mountain View (U.S. Army Corp of Engineers; June, 1959). In the lower reaches of the creek, flooding was more severe. Flooding is reported to have occurred near Middlefield Road, Barbara Road, EI Camino Real (to a depth of 2 feet), and in downtown Mountain View near Evelyn Avenue and Franklin Street (to a depth of 1 foot). Flooding in the vicinity of Bayshore Highway resulted in significant damage to both residential and agricultural properties. Damages in the Permanente watershed were totaled at $95,200 in 1958 dollars. Permanente Watershed -January 1963. Minor street flooding occurred in the Permanente watershed in January 1963. Permanente Watershed -January 1968. Minor street flooding occurred in Mountain View and Los Altos due to 1.48 inches of rain which fell within a 24 hour period. Permanente Diversion -March 2, 1983. On March 2, 1983, Permanente Diversion overtopped its banks and flooded Blach Jr. High School to a depth of 1/2 foot. Street flooding also occurred, as well as minor mud damage to the garages of three homes on Altamead Drive. The flooding was related to operations conducted at the Kaiser Cement Plant located in the upper Permanente Watershed. Immediately after the flood, Kaiser staff reported that the outlet to a large water "retention structure" had become plugged. On March 2, the plug burst, which resulted in the release of a large slug of water to Permanente Creek. County Communications reported that a large (about 20-foot deep) "wall" of water was observed traveling down Permanente Creek from Kaiser Cement. (Internal District memo, April 29, 1983) When the slug of water reached the box culvert near Blach Jr. High School, the water overtopped the banks. The capacity of the box culvert was significantly reduced due to sediment which had accumulated within the culvert. See Figure 3.1 for a map of the affected area. Permanente Creek and Hale Creek -January 1995. The storm of January 9-10, 1995, resulted in flooding on Permanente and Hale Creeks. Permanente Creek overflowed its banks causing damage to two units of an apartment building on Park Drive in Mountain View. The flood water in the apartments rose to a level of about 2 feet, and also inundated the adjoining Permanente Creek Flood Protection Project Page 35 Planning Study Report July 2008 garage, driveway, and a parking area. Hale Creek overbanked at Covington Road in Los Altos, resulting in street flooding. See Figure 3.1 for a map of the affected area. Permanence Creek and Hale Creek -February 1998. The storms of February 2 through February 7, 1998 resulted in over-banking of the west levee of Permanente Creek, immediately downstream of Amphitheater Parkway in the City of Mountain View. Floodwaters just barely spilled over the bank and into an empty lot adjacent to the creek. Permanente Creek also overtopped its banks just upstream of Park Avenue; minor flooding of a parking lot occurred. During the storm of February 2-3, 1998, Hale Creek overflowed its banks at Covington Road, Rosita Avenue, Arboleda Drive, and at the intersection of Mountain View Avenue and Raymundo Avenue. This resulted in minor street flooding. See Figure 3.1 for a map of the affected area. 3.1.2 Future Flooding Potential Although it is impossible to determine the exact location of future flood events, potential flooding problems along Permanente Creek, Hale Creek, and Permanente Diversion can be identified by developing maps of the expected flooding using hydraulic engineering numerical analysis software. The one-percent flood is the design flood for this project per the project objectives. The one-percent flood is defined as a flood that has a one percent probability of occurrence in any given year. This flood does not necessarily happen once in a hundred years; it can occur in consecutive years or even twice in the same year. Figure 3.2 depicts the areas subject to flooding from aone-percent event based on Federal Emergency Management Agency (FEMA) versus the District's definition of flooding. The major difference between the two flood mappings is that the District considers all areas that are inundated as flooded, while FEMA maps only show areas that experience greater than 0.3 meter (1 foot) flooding. Numerical models of Permanente and Hale Creeks and the Permanente Diversion show that approximately 3,200 parcels would be subject to flooding from aone- percentflood. 3.1.3 Reach Capacities Table 3.2 shows the results of a numerical modeling analysis showing the current capacities versus one-percent flows for all of the reaches of Permanente Creek in the project area. Reaches that do not have one-percent capacity are highlighted in red. As can be seen, most reaches of Permanente Creek are far below the capacity required for the one-percent flood. This is especially true in the middle creek reaches built in the 1960s. For Hale Creek, approximately half of the concrete portion and the majority of the natural portion cannot pass the one-percent flow. Permanente Diversion can generally pass the one-percent flow, with the exception of the portion between Grant Rd. and the Diversion's upstream end. There is a choke-point built into the channel upstream of Grant Rd. which controls the channel to 40 cubic meters per second (cros). This was built into the channel purposely to avoid induced flooding downstream in Stevens Creek. Stevens Creek currently does not have sufficient capacity to carry the one-percent flow (even with zero freeboard). 3.1.4 Manning's Roughness Coefficients Hydraulic calculations depend on appropriate modeling of channel conditions. One of the main channel parameters is the channel roughness factor, which is called the "Manning's n" number in the appropriate hydraulic formula. Proper selection of Manning`s n is crucial for the correct Permanente Creek Flood Protection Project Page 36 Planning Study Report July 2008 determination of channel capacity. For the Permanente Creek project, the following Manning's n numbers were used for the various channel types listed below. Table 3.1. Manning's n Factors Channel T e Existin Conditions "n" A Concrete 0.015 B Concrete with sediment 0.025 C Shot concrete rou h 0.020 D Stacked Concrete Wall made b ro ert owners 0.035 E Sacked Concrete Slo e Protection SCSP 0.030 F Sacked Concrete Slope Protection (SCSP) with rass 0.035 G Gro nes 0.035 H Silt mudd sediment invert 0.025 I Gravel-sized sediment invert 0.025 J Cobble-sized sediment invert 0.030 K Lar e rocks/boulder sediment invert 0.035 L Existin natural ve etation solid ve etation 0.100 M Existin natural ve etation limited under rowth 0.070 N Mature trees without round cover 0.050 O Grass 0.035 P Earth bench with rass/weeds 0.035 O Excavated earth 0.030 R Maintenance roads 0.025 S Overbank sections 0.025 For channels composed of more than one type of material, composite roughness factor was calculated using appropriate equations. The resulting Manning's n factors were used in the numerical modeling software to calculate creek capacities on a reach by reach basis, so that individual reach and bridge capacities could be calculated without interference from downstream or upstream reaches. The results are summarized in Table 3.2. Permanente Creek Flood Protection Project Page 37 Planning Study Report July 2008 Figure 3.2. FEMA and District Floodplains ,- _ _ _~~ 1 ,~ Permanente Creek Planning Study Parcels n Flood Plain 3170 Mt Viers 2'40 ~ MouFrtAlN vlFw Los Altos 430 ~' Permanente Creek -.. -- - - Watershed Boundary FEMA 1 % Flood Plain SCVWD 1'h. Flood Piam s Cupertino ? ~ „~ Los Altos J1 ~~ ~ I Los Altos Hills ~'`~-..; . Mountain View \, PaloAtto LOSALTpS } Sunnyvale ~ ~': San,a Clara County `~'` ,~ Unincorporated `q., ~ ` ,~ ,/ O i ~~~~- 1 ~~/ ~ _ G C 5 t ~ ~ wNNwALF ~ Miles __ / ~RN `~ . `~'f '` `'"'e: A~,,,"~/ e , ~ „ ' _. ~ LOS ALTOS NIILS ,~~ _ ,.. (J\~~ V S ° t ~,. IININCORDORATED CUDERTINO ``_\ ~\4~.1// DALO ALTO _ r ~~ ` \ l,~ ., ~ i~__ >: J i C J_ ~ DRFI IMINARY 7 28 08 _ ! I I S l`\ i\ Permanente Creek Flood Protection Project Page 38 Planning Study Report July 2008 Table 3.2. Current Creek Reach Capacities Permanente Creek Location: 1 % Flow CMS CFS Reach Capacity CMS CFS jdfi ! irllii.;,l,U !S,y l~_ t~ .. i:l' 1 ,,( ;.'~tIC I i_ii~l:::: t>l.i(1 Y_; ~VL) to Boat Pond Salt Ponds 74 2600 30 1050 EE Boat Pond to Shoreline 74 2600 148 5200 Shoreline Parkway Bridge 74 2600 100 3500 Shoreline to Rengstorff 74 2600 100 3500 Rengstorff Walkway Bridge 74 2600 100 3500 ~',.;~~~~.~>tCilit to ~i<)li ~.UiiiSc /~'1 ~_fji_)(1 ,, ~'(_)OU Golf Course Bridge 74 2600 Ea4 2250 Golf Course to New Ditch 7~1 2600 66 2300 New Ditch Bridge 74 2600 44 1550 Nei.^~~ Ouch to Amphitlril~ r 74 2600 43 1500 Amphitheater Parkway Bridge 74 2600 131 4600 A~~.~„!~iii~erate( tc?C.i~:a~~~~:_;>~~;,~ 74 2600 44 1550 Charleston Road Bndge 74 260^i 73 2600 Charleston to Hwy 101 74 260i? 40 1400 Highway 101 Bridge 74 2600 42 150(:) Hwy 101 to Old Middlefield 71 2500 40 1400 Old Middlefield Way Bridge 71 2500 27 950 Old Middlefield to Rock 71 2500 52 185; Rock Street Bridge i 1 2500 35 1250 Rock to Middlefield 71 -?500 58 205: Middlefield Road Bridle i 1 2500 38 1350 Middlefield to San Ran~o(~ 71 2500 65 2300 San Ramon Avenue Bridge ~ i 2500 37 1300 San Ramon to San Luis 71 2501 ~ 47 1650 San Luis Avenue Bridge 71 2500 51 1800 San Luis to Montecito 71 2500 50 1750 Montecito Avenue Bridge 71 2500 43 1500 Montecito to Hackett 71 2500 53 1900 Hackett Avenue Bridge 71 2500 55 1950 Hackett to Hetch Hetchy 71 250Ci 57 2000 Hetch Hetchy Bridge 71 2500 27 950 Hetch Hetchy to Central 71 2500 31 1 100 Central Expressway Bridge 71 2500 33 1 150 Central to SPRR 65 2300 92 92 SPRR Bridge 65 2301) 38 1350 SPRR to Villa 6~~ 2300 28 1000 Villa Street t;~~~,~ . 2;300 34 1200 Permanente Creek Flood Protection Project Page 39 Planning Study Report July 2008 Table 3.2. Current Creek Reach Capacities (continued) Permanente Creek Location: 1 % Flow CMS CFS Reach Capacity CMS CFS Viiia l,lti',~~_~i it_i (~ ..:ii!i .. .~.ulv"il ..,.. ,~'(~ ,_i-~ ~ ,. . EI Camino Real Culvert 65 2300 34 1200 EI Camino Real to Private E3ricfge 65 2300 36 1250 Private Bridge 65 2300 36 1250 Private Bridge to Palk 65 2300 36 1250 Park Drive Bridge 65 2300 28 1000 Park to Mountain View 65 2300 18 650 Mountain View Avenue Bridge 65 2300 21 750 Mountain View to Hale Creek Confluen~,e E>5 2300 18 650 Hale Creek Confluence to Marilyn 40 1400 10 350 Marilyn Drive Bridge 40 1400 8 300 Marilyn to Barbara 40 1400 6 200 Barbara Avenue Bridge 10 1400 7 250 Barbara to Miramonte/Cuesta X10 1 ~OC~ 8 300 Miramonte/Cuesta Culvert ~~~ ~ 4(~~O 12 400 Miramonte/Cuesta to Villa Siena 37 13Ci0 16 550 Villa Siena Bridge 37 1300 1 7 600 Villa Siena to St. Francis Walkway 1300 19 650 St. Francis Walkway Bridge ~~' 13i)~~ 25 900 St. Francis Walkway to St. Francis Exii ., 1:>UO 25 900 St. Francis Exit Bridge 37 1300 25 900 St. Francis Exit to St. Francis Entrance 3:' 1300 27 950 St. Francis Entrance Bridge ";7 1300 20 700 ~t 1-~,-~,;;_ ~ ,~ , ~,~~> tc~ Atandoned Bridge #30 3% '~!~0 25 ~1i~C, Abandoned Bridge #30 37 1300 40 1400 ^., r,~~, 3,-~! ~ I;-~, ,,~~ ;~~~i~ to Abandoned Bridle ~~ 31 1 ~ s.~,ri ;~, ~, Abandoned Bridge #31 3i 1300 23 800 Abandoned Bridge #31 to Covington 37 1300 1 h 550 Covington Road Bridge 37 1300 14 .500 Covington to 54" Diversion Pipe 3 i 1300 9 300 54" CMP (r7ote. pipe regi_ilarfy clogs with sediment) 37 1300 (' zO0 Div r ;icy„ !; Gage its 2700 1; :~,~~ Gage Bridge 76 2700 159 5600 Gage to Portland 76 2700 82 2900 P~_:~'~~ia~d <+ . _: Bridge i6 2700 ~;y ?~)0 Portland to Aura 76 2700 c7 950 Permanente Creek Flood Protection Project Page 40 Planning Study Report July 2008 Table 3.2. Current Creek Reach Capacities (continued) 1 % Flow CMS CFS Reach Capacity CMS CFS Aura Way Bridge !': 90 Aura to Fremont ;'E~ _ ;'v0 134 ~ , (~~;` Fremont Avenue Budge ,,%t~ 2700 182 E~4UC! Fre~r~~ ~~ ~1 to Foothill i (; 2700 172 ~ t ,:'ii Hale Creek Location: Permanente Creek to Mt. View 31 1100 56 2000 Mt_ View ,~'+eC.llut: Bridge 31 1 100 22 Mt. View to Arroyo 31 1 100 22 ~~00 Arroyo Road Bridge 31 1100 52 1850 Arroyo to Marilyn 31 1100 35 1250 Marilyn Drive Bridge 31 1100 35 1250 Marilyn to 7`h Day Adventist 31 1100 41 1450 7'° Day Adventist Bridge 31 1 10O 18 +.»v 7'' Day Adventist to Nui it ~ 5ui ~sh,r~e ~ 1 1 10O ?h ~~00 North Sunshine Drive Bridge 3 ~ 1 10(l ? ti ~ ~~50 i U~ ~ .,;I'ti~ ~,~C ~~ '~ ',i~1S-Mile., ~'' 1 ?~~'~, South Sunshine Drive Bridge 31 1100 42 1500 Sc>u11 ~ ~u~ ~ >~ \, , t; ;. ~}r ~ 1 100 Springer Road Bridge :~ ? 1 1(i(; 23 800 Springer to 400 Springer _ . 1 10%7 30 ? 050 ~(1O `.~t„irt~1E'I R"~iC_1 C-~Iitj~-ark 31 1 1OO %~E~. 400 Springer to Cuesta 31 1100 42 1500 Cr~~.., ; ,~~~~~~r~~:~ f;~ ~i~~r~ 31 1100 21 Cuesta io Arboleda 3 1 1 100 2~3 1000 Arboleda Avenue Bridge 3 i 1 100 23 800 Arboeda to Rosita (including 4 private bridges) 31 1 100 20 700 Rosita Avenue Bridge 31 1 10(~ 23 X00 F3osit~_, Ic f~~u~k Rip-Rap Section 24 330 15 ~~~50 Rock Rip-Rap Section 24 830 25 900 Rock Rip-Rap Section to Covington 24 830 15 550 Covington Road Bridge 24 830 10 350 C~win~:lfun !:~ F~c>>,[I~il f=x~,iE~s~v~ray 24 830 11 400 Permanente Diversion Location: Hwy 85 Bridge 40 1400 65 2300 Hwy 85 to Diericx 40 1400 113 4000 Diericx Drive Bridge 40 1400 51 1800 Diericx to Grant 40 1400 68 2400 Grant Road Bridge 40 1400 105 3700 Gi~~nt try Pern~~:-~; E?rrte Creek 40 1400 <10 140u Permanente Creek Flood Protection Project Page 41 Planning Study Report July 2008 Stevens Creek Location: Sir; ~rarx;isco E3ay to Highway 101 229 81 UO 16~ 5800 Highway 10l to EI Camino Real 221 7800 108 3800 EI Camino Real to Permanente Diversion 218 7700 227 8000 3.2 Local Drainage Conditions Local drainage is not identified as a major problem in the Permanente Creek watershed. The majority of the watershed area drains to the creek system either through overland flow (in the undeveloped upper watershed) or through city storm drain systems. The levee portion of the watershed north of Highway 101 also drains to the creek through gravity flows, which becomes ineffective when creek levels are high. 3.3 Maintenance Access In order to maintain the creek, maintenance staff must be able to access the creek. Access to Hale Creek, and access to Permanente Creek upstream of Highway 101 is difficult, costly, and often severely limited because the District holds a very narrow maintenance easement along the creeks. Downstream of Highway 101, maintenance roads located on the top of the levees provide access to most of Permanente Creek. Since crews and equipment can operate on the top of the levees, out of the creek bed, access to the creek is generally possible year-round. Along Hale Creek, and along Permanente Creek upstream of Highway 101, there are no maintenance roads; creeks are generally accessed at bridge crossings. In order to maintain the creek between bridges, equipment must be moved along the bottom of the creek bed, which typically prohibits maintenance of these areas during periods of medium and high flows. In most areas where the creeks flow through concrete channels, vehicular access is possible during periods of low flows by driving along the invert of the creek. In areas were the creeks are in asemi-natural state, no vehicular access is possible. A brief description of existing maintenance access for each section of Permanente and Hale Creeks within the project study area is presented below. PERMANENTE CREEK Reach P1: Maintenance access is poor; the levees are owned by US Fish and Wildlife Service and vegetation is not regularly controlled to allow for vehicular access. Reach P2: Maintenance access to this area is available along maintenance roads located on the tops of the levees. Reach P3: Maintenance ramps located at several locations allow maintenance vehicles access to the creek during periods of low flow. During periods of medium and high flows there is limited access to the creek because maintenance crews cannot move along the bottom of the channel. Permanente Creek Flood Protection Project Page a2 Planning Study Report July 2008 Reach P4: Maintenance ramps allow limited access to the downstream end of the Villa St. culvert and the upstream end of the California/EI Camino culvert during low flows. There is no access to the remainder of the culvert, with the exception of a few drop inlets. Reach P5: This section can be accessed only by a maintenance ramp located at Mountain View Avenue. During periods of medium and high flows there is limited access to the creek because maintenance crews cannot move along the bottom of the channel. Reaches P6 and P7: There is very little access for maintenance vehicles along these entire reaches. Access is limited to the areas next to Miramonte Avenue. Reach P8: Maintenance ramps allow access to the invert of the creek in the downstream portions of the reach; however, vehicular access may be impaired by drop structures. There is little access in the upstream portion of the reach. HALE CREEK Reach H1: Maintenance ramps located at several locations allow maintenance vehicles access to the creek during periods of low flow. During periods of medium and high flows there is limited access to the creek because maintenance crews cannot move along the bottom of the channel. Reach H2: There is very little access for maintenance vehicles along the entire reach other than at bridge crossings. PERMANENTE DIVERSION Reach PD: Maintenance ramps located at several locations allow maintenance vehicles access to the creek during periods of low flow. During periods of medium and high flows there is limited access to the creek because maintenance crews cannot move along the bottom of the channel. There is some top of bank room available. 3.4 Erosion and Sedimentation Due to the shearing effects of the highly active local fault zones, creeks originating in the Santa Cruz Mountains typically have high amounts of natural sediments associated with high volume flow events. In addition to this natural background level sediment production, three factors increase sedimentation in the Permanente/Hale watersheds. Hanson Permanente Cemenf Plant The plant operates on the southern fork of the upper Permanente watershed. The mining activities generate tremendous amounts of "waste rock", which are stored on site, sometimes in very close proximity to the creek. The activities also produce smaller sand particulates and dust, which can be carried to the creek during storm events. In response to concerns from the Permanente Creek Flood Protection Project Page 43 Planning Study Report July 2008 public and regulatory agencies such as the Regional Water Quality Control Board (RWQCB), the plant has devised various methods to trap the waste materials and dust from being carried into the creek. These methods include interception ponds, flow diversion from work sites, in- stream sediment catch basins, etc. The plant reports annually to the RWQCB on how they are meeting their storm water pollution prevention plan (SWPPP) goals. Urbanization Urbanization also causes increased sediment production in Santa Clara Valley. Urbanization causes dramatically more rapid and higher peaks in creeks for the more frequent flows (1- to 10- year events). The higher flows cause a response in natural channels, which classically consists of down-cutting (getting deeper) and then bank erosion (getting wider) to be able to handle the increased flows. During this channel adjustment period, which can occur over decades even if urbanization has been completed, the deepening and widening creates much higher than normal sediment loads for downstream sections. The other effect of urbanization is to route road deposits such as metals and petroleum products into storm drains and thus into the receiving waters. This issue has previously been identified as a source of pollution to both creeks and the southern San Francisco Bay. Tidal Sedimentation In the reaches of Permanente Creek subject to tidal influence (approximately upstream to Highway 101), tidal sedimentation is a maintenance concern. Generally, the process for tidal sediment creation involves waves in the shallow southern sections of San Francisco Bay stirring up very fine sediments (bay mud) from the bottom of the Bay. The diurnal tides carry this sediment up the various creek channels. As the tides turn, the flow velocity drops to near zero, and a small amount of sediment can deposit on the channel bottom. These sediments would generally wash away during severe winter events; however, the sediments tend to attract saltwater marsh vegetation, such as bulrush and cordgrass, which stabilize the sediments in place. Sedimentation in the tidal sloughs thus tends to occur inward from the banks. 3.4.1 Sedimentation Locations Significant sediment deposition has historically occurred at two locations (see Figure 3.3) in the Permanente watershed: 1) on Permanente Creek near Highway 101; and 2) in the Permanente Diversion and in Permanente Creek immediately upstream of the Diversion. Minor sedimentation problems also occur along Hale Creek and its tributaries. Significant sedimentation problems in the Permanente Watershed are described below. Permanente Creek -San Francisco Bay to Highway 101 Significant sediment deposition occurs along the lower reach of Permanente Creek from the San Francisco Bay upstream to Highway 101. In South San Francisco Bay, a large percentage of the fine sediments found in tidal reaches are transported from the Sacramento Delta down to the South Bay where the sediments are deposited in areas sheltered from waves and tidal currents (Krone 1972). Most of the sediment removed from Permanente Creek downstream of Highway 101 consists of fine clays and silts, Permanente Creek Flood Protection Project Page 44 Planning Study Report July 2008 and it is therefore likely that tidal action is responsible for the majority of sedimentation downstream of Highway 101. Periodic sediment removal between Amphitheater Parkway and Highway 101 has been performed by the District in order to increase the carrying capacity of the creek and minimize the threat of flooding. Between May 1979 and May 1998, sediment removal was conducted on seven different occasions between Amphitheater Parkway and Highway 101. A total of 3,640 cubic meters (4,758 cubic yards) of sediment have been removed over the 19 year period; the average volume of sediment removed from this area is 190 cubic meters (250 cubic yards) per year. Permanente Diversion and Permanente Creek near the Diversion Significant sediment deposition also occurs along Permanente Diversion and along Permanente Creek immediately upstream and downstream of the Diversion. This sediment has been transported downstream from the upper reaches of the Permanente watershed. Sediment deposition occurs along the U-frame portion of the Diversion due to the mild slope of the channel combined with a larger than average bottom width. Sedimentation also occurs in the 54-inch culvert on Permanente Creek which crosses under Eastwood Drive. The pipe is located just downstream of the beginning of the Permanente Diversion Channel. The Diversion was designed so that the base flows would be carried by Permanente Creek, and higher flows would be carried by the Diversion. However, heavy sediment deposition within the 54" culvert has repeatedly blocked it and prevented flows from traveling down Permanente Creek. District maintenance staff reports that one or two large storms are enough to completely fill the culvert with sediment and block all flows through it. Removing the sediment from the culvert has proved to be very difficult and costly. Due to these problems, the District's present mode of operation is to close the gate to the 54" culvert every year between October 15 and April 15, in order to minimize sediment deposition in it. Periodic sediment removal along Permanente Diversion and Permanente Creek (between Eastwood Drive and Portland Avenue) has been performed by the District in order to maintain the capacity of the creek and minimize the threat of flooding. Between May 1979 and May 1998, sediment removal was conducted on 22 different occasions along Permanente Diversion and Permanente Creek between Eastwood Drive and Portland Avenue. A total of 35,000 cubic meters (45,800 cubic yards) of sediment have been removed over the 19 year period, the average volume of sediment removed from this area is 1840 cubic meters (2,410 cubic yards) per year. It should be noted that very little sediment removal occurred from the mid 1980's through 1991. This period coincided with a drought in Santa Clara County. Decreased stream flows typically result in decreased sedimentation and erosion; therefore, it is likely that the drought contributed to the reduced need for sediment removal during this period. Hale Creek and Tributaries Sedimentation occurs along Hale Creek and its tributaries; however, the rate of sedimentation is much less than the upper reaches of Permanente Creek. Between May 1979 and May 1998 there is only record of a single sediment removal activity, which occurred (outside of the project reach) on Magdalena Creek in 1988. Permanente Creek Flood Protection Project Page 45 Planning Study Report July 2008 / ~f' ;, ~'~ AVERAGE ANNUAL ' SEDIMENT REMOVA(= r I, 150 CUBIC YARDS `t _ c W C¢ r i~ rS ~, _. 1 l t.. Y ~~ _.. __ ®'. AVERAGE ANNUAL SFDINFNT REMOVAL = j 2400 CUBIC YARDS Permanente Creek Sediment Removal Legend _ _ j'~ i Area fo Sediment Removal SCVWD Flooding o o s i~ Miles Figure 3.3. Sediment Removal Locations Permanente Creek Flood Protection Project Page 46 Planning Study Report July 2008 3.4.2 Bank and Invert Erosion Within the Permanente watershed study area there is significant erosion in many of the semi- natural earthen channels. There are four stretches of semi-natural earthen channels within the study area: Permanente Creek from San Francisco Bay to Highway 101; Permanente Creek from the Hale Creek confluence to the Permanente Diversion Channel; Permanente Creek from Portland Avenue to Foothill Expressway, and Hale Creek from Rose/Rosita Avenue to Foothill Expressway. Permanente Creek -San Francisco Bay to Highway 101 Minor levee erosion occurs in the area at several outfalls. There is no evidence of invert erosion. Permanente Creek -Hale Creek Confluence to Permanente Diversion Channel Some erosion of the creek banks occurs throughout this reach. The creek channel is very narrow, and is highly encroached upon by surrounding residential properties. Bank slopes are typically steep. In many areas the slopes approach vertical. Numerous patchwork attempts at bank stabilization have been made in this area by the District and by private parties. Bank stabilization methods used in this area include sacked concrete, wooden retaining walls, and concrete rubble and rock retaining walls. There is very little evidence of invert erosion along this reach. Permanente Creek -Portland Avenue to Foothill Expressway Some minor erosion of the creek banks occurs throughout this reach. Although the creek bed is significantly wider in this reach than in the downstream reaches, the channel is very deep and the banks are steep. There is scattered use of sacked concrete in this reach, especially at creek bends along the outside bank. In several areas the toe of the sacked concrete has become undercut by some mild invert erosion. The invert erosion appears to be progressing very slowly, if at all, indicating that the channel may be establishing dynamic equilibrium post-urbanization. Hale Creek -Rose/Rosita Avenue to Foothill Expressway Some relatively minor erosion of the creek banks occurs throughout this reach. The creek channel is narrow, and is highly encroached upon by surrounding residential properties. Bank slopes are steep in many areas, especially at creek bends. Patchwork attempts at bank stabilization have been made in this area by the District and by private parties. Bank stabilization methods used in this area include sacked concrete, wooden retaining walls, and concrete rubble and rock retaining walls. There is little evidence of invert erosion along this reach. Permanente and Hale Creek -Upper Watershed Areas This reach of the watershed is technically outside of the project area, as defined by the Clean, Safe Creeks project objectives. The creeks in this reach are experiencing bank and invert Permanente Creek Flood Protection Project Page 47 Planning Study Report July 2008 erosion associated with increased flow due to urbanization. The District has recently conducted bank and invert stabilization projects for both Hale Creek and Permanente Creek. On-going monitoring and maintenance activities may be required into the foreseeable future. 3.5 Structural Deterioration of Previous Work The Permanente Diversion was constructed in 1959 and most of the remaining concrete channel work was completed in the early 1960's (see Figure 3.4 -Channel Types). Engineering projects are built with assumed life spans, although many perform their intended service far longer than planned. Permanente Creek and Hale Creek, however, have deteriorated to the point that some reaches are in severe risk of failure. A structural study of the channels was commissioned in 1999. The structural engineering firm of Biggs Cardosa Associates conducted a thorough study of the current condition of the channels, predicted future performance, and recommended certain possible rehabilitation or replacement options. The study found that much of the work conducted in the 1960's has deteriorated and significant lengths of the constructed channels are in danger of failure. The failure mechanisms vary, with the most worrisome being vertical banks toppling into channels. The study also developed a mechanism for estimating the remaining service life for the channels (See Figure 3.5 -Remaining Service Life). A small percentage of channel length was thought to be in danger of imminent failure; but the majority of channel length was determined to be in high risk of failure during the next 15 years (from 1999). 3.6 Permanente Diversion Flow Split Due to poor design, the 54" culvert (which represents Permanente Creek) does not function as intended at the point of the diversion to Stevens Creek. The inlet to the culvert (at the bottom of the channel) as well as the culvert itself are severely prone to sedimentation and are extremely difficult to restore once silted in. To avoid this problem, the culvert is screened off from flows every winter, in effect making the diversion to Stevens Creek the only conveyance for upper watershed flow. Thus, lower Permanente Creek typically conveys very little of its upper watershed flow. This is not the way the flow split at the diversion was envisioned. Approximately half of the flow was to be conveyed via the diversion, with the half flowing down Permanente Creek. This incorrect flow split further reduces the already limited capacity of the Permanente Diversion by eliminating any flow from being carried by the natural channel downstream. The effect is that the capacity of this location is reduced to just the capacity of the Diversion (see above). Permanente Creek Flood Protection Project Page 48 Planning Study Report July 2008 t ~x 1~ ~ r ~~ :¢ i i~ ~i ~'l ® t / L i ~ \~ - Permanente Creek and Hale Creek Channel Types Legend °_ Earth Levee $ Concrete Box Culvert ~'~ Concrete Trapezoidal ~ SCVWD Flooding /'\ ~ Channel - Urnmproved Earth SCVWD Creels Channel 0 0.5 1 Concrete U-frame 1Nater Bodes Channel ~ Miles Figure 3.4. Channel Types Permanente Creek Flood Protection Project Page 49 Planning Study Report July 2008 % ~ i ~ ~ ~ i ~ `.. g Q I ~ ~ I ~~l .. ~~ ~ r' ~ = 1 C t`; 1 ~ - - _ . ~. - .~~;F. r_~, v Legend Permanente and Hale Creek & ~0-5 years Permanente Diversion 5-i0 years /~; ` Remaining Life io-is years I\ 0 15-20 years 0 O 5 1 20-25 years Miles u ~ 35-40 years Figure 3.5. Remaining Service Life Permanente Creek Flood Protection Project Page 50 Planning Study Report July 2008 3.7 Sea Level Rise The levee portion of the watershed (north of Highway 101) is subject to bay tidal influence. Therefore, any rise in sea levels due to climatic variations or other causes could increase the starting downstream water surface elevation and i~~crease the risk of flooding. Increases in sea level could also result in more extensive landward encroachment of tidal processes, including salinity and bay sediment deposition. Permanente Creek Flood Protection Project Page 51 Planning Study Report July 2008 Permanente Creek Flood Protection Project Page 52 Planning Study Report July 2008 CHAPTER 4 FORMULATION OF ALTERNATIVES This chapter describes the range of alternatives considered for the Permanente Creek Flood Protection Project and the methodology followed to determine the recommended project. 4.1 Alternatives Approach The alternatives development approach for the project was as follows: • Identify all conceptual project elements ca~~able of meeting the project objectives, whether reach-oriented (e.g. channel improvements), regional (e.g. flood detention), or property-specific (e.g. flood proofing) • Identify potential opportunities for environrr~ental enhancement project elements • Construct conceptual alternatives made up of one or more of the project elements identified, representing possible solutions tic the project's objectives • Conduct level 1 screening, identifying whicl~ conceptual alternatives are feasible for further consideration • Rate the feasible alternatives as to how well they meet the District's Natural Flood Protection (NFP) objectives • Select the recommended alternative based on the outcome of the NFP objectives rating 4.2 Conceptual Project Elements Throughout the project planning phases, the proje~;t team has worked to identify a number of approaches to meet the project's flood protection rind environmental enhancement objectives. Each of these approaches was referred to as a co~~ceptual project element (CPE). Some of the CPEs were capable of offering astand-alone solution, while others were intended to be used as building blocks that could be combined to form a variety of integrative solutions addressing the project's objectives. That is, the proposed project would consist of one or a combination of several separate elements addressing the needs c-f different parts of the creeks. Some of the constraints placed on project element identification included: • The project cannot exacerbate the flooding issue in the Stevens Creek watershed; the project must solve Permanente Creek's floeding problems within the Permanente watershed. • The project does not need to address the general tidal flooding problem; however, the project should be compatible with future tidal flood protection efforts. Sources of information used to create the CPEs included previous District studies, input from resource agencies, local jurisdictions, and members of the public. Hydraulic, hydrologic, Permanente Creek Flood Protection Project Page 53 Planning Study Report July 2008 wetlands, habitat research, and other work supported the CPE identification effort. There are four basic categories of flood protection improvement project elements: • Structural improvement: project elements such as channel widening and steepening, levee and floodwall raising, and bridge and culvert replacement. The aim is to increase the amount of flow the channel can carry. • Bypasses and diversions: the concept is to route excess (flooding) flows around low- capacity portions of the creek through a new channel separate from the creek itself. This is frequently useful in increasing the effective capacity of the creek in reaches where the creek itself cannot be changed, due to concerns about environmental or utility impacts. • Flood peak detention: the concept is to reduce the peak flowrate downstream by storing the peak of the flood in an off-stream or instream detention area. The reduced flows then can pass safely though existing creek infrastructure downstream, reducing the need for structural improvements. • Flood proofing: the concept is to protect the areas in danger of flooding instead of preventing creek flooding itself. Structures can be raised on new foundations, moved from the flood-prone area, or shielded from flood flows. After the early planning phase of analyzing the watershed's hydrologic and hydraulic characteristics, the following observations and conclusions were made: The flooding problem is widespread in the project area. Except for a few short reaches, the entire channel length lacks the capacity to pass the one-percent flow downstream. This means that structural/bypass project alternatives will involve a very significant and widespread effort. Analysis of the pattern of flooding reveals that during the large flood events, the initial breakout points are far upstream in the project reach. Hale Creek would initially break out of the channel at Covington Road and Permanente Creek would break out at Blach School. Due to the watershed topography and lack of creek capacity downstream, once floodwaters break out, they don't return to the channel, but flow parallel to the creek in a generally northward direction towards Highway 101, where they pond against the higher ground. Therefore, simply improving the channel structure from the Bay to EI Camino Real, as was originally envisioned in the Clean, Safe Creeks measure, would not remove any of the floodplain area; a floodplain interceptor channel would be needed to catch the floodplain flows and convey them to the improved channels. Hydrology analysis reveals that the peaks of the design floods, especially the peak between the ten-percent and one-percent flows, is quite sharp. That is, the period of time it takes the flow to go from ten-percent to one-percent and back down again is a matter of a few hours. For example, South Branch Permanente Creek in the vicinity of Rancho San Antonio goes from the ten-percent flow to the one-percent flow and back down to ten-percent in three hours. This observation implies that relatively little storage volume is required in order to significantly reduce peak flows downstream through flow Permanente Creek Flood Protection Project Page 54 Planning Study Report July 2008 detention. Therefore, the potential for flow detention project elements should be fully investigated. 4.3 Conceptual Project Elements Developmenit A total of 21 CPEs were identified (CPE 1 to CPE 21). Broad, qualitative data was used to identify as wide a variety of approaches as practicable. The first set of 18 CPEs was presented to the Permanente Creek Task Force (Task Force- in September 2004 and subsequently presented to the Public in November 2004. Additi~~nal CPEs have been developed over the following years. The identified CPEs (see Appendix A for information sheets on the first 18 CPEs; CPEs 19, 20, and 21 are covered under fe~isible alternatives) were: CPE 1: No Project: This project element would c~~ntinue the current maintenance program for the watershed area. Current sediment, vegetation, and bank repair efforts would continue. Additionally, the current monitoring of the deterior~iting concrete channels built in the 1960's and their replacement as needed would continue. CPE 2: South Branch Dam: This project element would involve building a 100-foot high by (approximately) 500-foot wide concrete dam on the South Branch Permanente Creek in lands owned by Hanson Permanente Cement Plant. The storage volume at the spillway elevation would be approximately 325 acre-feet with an inundation area of approximately 12 acres. The dam would have an opening sized to permit up to 50 cubic feet per second (cfs) to freely outflow; therefore the dam storage area would be empty most of the time (when flows are less than 50 cfs). This project element would reduce the flood peak downstream by approximately 500 cfs. CPE 3: Rancho San Antonio Flood Detention: This project element would involve building an 8-acre flood detention area adjacent to South Branch Permanente Creek in Rancho San Antonio Park. The detention area would be in a current meadow location between Gate of Heaven Cemetery and the park's equestrian parking area. The detention area would be 15 feet deep, with variable, mild side slopes and invert to resemble natural relief and could be vegetated as desired. Flows higher than approximately the ten-year event would spill into a diversion swale and be temporarily stored in the detention area. Once the flood peak would pass, the stored flood flows would drain back into the creek (by gravity flow) and the detention area would be empty again in 1-2 days (dependinl~ on the flood event). This project element would reduce the flood peak downstream by approximately 700 cfs. CPE 4: Grant Road Flood Detention: This project element would involve building a detention pond in the 15-acre parcel located on Grant Road near the Permanente Diversion. The size and depth of the detention varies from 3 acres anti 15 feet deep to the full site at 20 feet deep, depending on the alternative. The detention area invert would be converted to athletic fields or other open space uses. CPE 5 McKelvey Park Flood Detention: This pr~~ject element would involve building a detention pond in the 5-acre baseball facility owned by the City of Mountain View. The park is located at the corner of Park Drive and Miramonte Avenue. The entire park would be lowered approximately 15 feet deep, with all-new facilities I~uilt at the new field level. Flows higher than approximately the ten-year event would spill over ;~ weir and into an energy dissipation area. From there, flood waters would spread into the de~rention area for temporary storage. Once the flood peak would pass, the stored flood flows would drain back into the creek (by gravity flow) and the detention area would be empty again in 1-2 days (depending on the flood event). The Permanente Creek Flood Protection Project Page 55 Planning Study Report July 2008 fields would be cleaned up by the District and readied for play. This project element would reduce downstream peak flow by approximately 400 cfs. CPE 6: Hale Creek Diversion: An 8-foot by 8-foot concrete culvert 4000 feet long would be built to convey peak flows to Permanente Creek upstream of the Permanente Diversion. The concept was to reduce the peak flows in Hale Creek sufficiently such that very little structural improvement work would be needed downstream. CPE 7: Hale Creek Bypass: This project element proposed to build ahigh-flow under street culvert to bypass the natural portion of Hale Creek (from south of Covington Road to Rosita Avenue). The bypass would be approximately 8-foot by 8-foot and 3000 feet long. The concept was to increase creek capacity while avoiding impacts to the natural portion of Hale Creek. CPE 8: Permanente Bypass: This project element proposed to build ahigh-flow under street culvert to bypass the natural portion of Permanente Creek. The length, size, and route of the culvert are variable, depending on the particular alternative. The concept was to increase creek capacity while avoiding impacts to the natural portion of the creek. CPE 9: Floodwalls: This project element can be divided into two main reaches: north of Highway 101 and South of the Highway. North of Highway 101, the project element involved building floodwalls on top of the existing levees north to the high grounds of Shoreline Park (just north of Amphitheater Parkway). The height of these floodwalls varies between 5-7 feet for structural alternatives and 2-3 feet for flow detention alternatives. South of Highway 101, the concept would be to remove the existing concrete channels and replace them with concrete floodwall channels. The floodwalls would range from 8 feet high downstream to higher than 20 feet high near EI Camino Real. CPE 10: Channel Widening: This project element involves the concrete channels along reaches P3, P5, and H1. The concept was to increase channel capacity by widening and steepening (removing drop structures) the existing concrete channels and bridges within existing District right-of-way. The specific work reaches and bridges impacted vary depending on the specific alternative. CPE 11: Geomorphic Stream Restoration: All existing concrete channels in reaches P3, P5, and H1 would be removed. A row of parcels next to the creek channel in these reaches would be acquired and the existing structures removed. A meandering natural creek channel with appropriate dimensions, layout shape, floodplain, and flood bench would be built. All bridges and culverts along the reaches would be modified appropriately for floodway connectivity. CPE 12: Riparian Restoration: The original concept was for the deteriorating existing concrete channels in reaches P3 and H1 to be removed and replaced with earth channels with riparian vegetation. This could only be done in conjunction with flood detention project elements, since the peak flows would have to be reduced to make the concept work. CPE 13: Non-structural (flood proofing): The parcels in the floodplain would be directly protected through structural elevation or flood shielding. Structural elevation would involve raising the structures above the flood elevation and placing them on new foundations. Flood shielding would involve surrounding the perimeters of the flooding properties with waterproof shielding. Permanente Creek Flood Protection Project Page 56 Planning Study Report July 2008 CPE 14: Seventh Day Adventist Church Flood Detention: An off-stream detention facility would be created on the back-lot of the 7th Day Aclventist Church property on Springer Road. The back parcel is approximately 1.7 acres in size. The average depth would be 10 feet, producing 17 acre-feet of volume. The existing house on the parcel would have to be removed and replaced with a new house in the neighborhood. This CPE could reduce peak flows in Hale Creek by 200 cfs. CPE 15: EI Camino Bypass: An underground bypass consisting of a 10-foot by 10-foot box culvert would be constructed under existing streets around the current EI Camino Real to Villa Street culverts. The length of the bypass would v,~ry, depending on the alternative. The aim would be to increase channel capacity such that tl~e existing culverts would not need to be improved. CPE 16: EI Camino Culvert: The existing culverts from EI Camino Real to Villa Street would be improved from within (enlarged) by having their inverts lowered by 3-10 feet. This would increase the culvert capacity such that the entire one-percent flows could be contained. CPE 17: Hale Creek Improvements: The existing concrete channel along Reach H1 would be improved by the invert section being lowered and drop structures removed to within existing District right-of-way. This would improve capacity to the full one-percent flow rate. CPE i8: Flood Collection Channel: Anew undE~rground 8-foot by 8-foot box culvert would be installed under one lane of EI Camino Real to capture floodwaters from upstream flood breakout points and convey them to the improved concrete channels. Grated inlets installed along EI Camino Real would capture the flood flows and cc-nvey them to the culvert. CPE 19: New Diversion Structure: The existing flow diversion structure at the upstream end of the Permanente Diversion Channel does not function as intended. Currently, all flows, including low flows continue down the Diversion Channel to Stevens Creek. The new diversion structure would correctly split the flow between thE~ natural portion of Permanente Creek and the Diversion Channel such that low flows would flow down the natural Permanente Creek. The exact dimensions of the new structure would vary, depending on the alternative. CPE 20: Cuesfa Park Annex Flood Detention: 'This project element would involve building a flood detention area in portions of the Cuesta ParE; Annex and, in some alternatives, the parking area of Cuesta Park itself. The detention area would be 15 to 20 feet deep, with variable, mild side slopes and invert to resemble natural relief ar~d could be vegetated as desired. Flows higher than approximately the ten-year event would be temporarily stored in the detention area. Once the flood peak would pass, the stored flood flows would drain back into the creek (by gravity flow) and the detention area would be empty again in 1-2 days (depending on the flood event). CPE 21: Bloch School Flood Detention: This project element would involve building a flood detention area in the football field/track portion of 131ach School's open space area. The detention area would be 15 feet deep, with 2:1 side slopes and the football field and track area rebuilt at the bottom of the detention area. Flows (higher than approximately the ten-year event would be diverted out of the Permanente Diversion and temporarily stored in the detention area. Once the flood peak would pass, the stored flood 1~lows would drain back out of the area (by gravity flow) and the detention area would be empty again in 1-2 days (depending on the flood event). The fields would be cleaned up by the District and readied for play. Permanente Creek Flood Protection Project Page 57 Planning Study Report July 2008 4.4 Conceptual Alternatives Development Once the potential CPEs were identified, conceptual alternatives were identified by combining the CPEs in various sets. Although a very large number of potential combinations are theoretically possible, many of the combinations would not make sense in terms of meeting the project objectives. This is because many of the CPEs provide benefits in certain locations and in certain combinations and are superfluous when combined with other CPEs. A total of 26 conceptual alternatives (alternatives A through Z) were identified. Note that all conceptual alternatives, other than alternative A (No Project) include CPE 19, which proposes to replace the existing flow split structure at the upstream end of the Permanente Diversion with a new flow structure that would provide a more effective flow split with reduced maintenance issues. The figures provided for the cost estimates were order of magnitude costs produced for the rough conceptual alternatives stage in 2005 dollars. Since the CSC aim of the design/construction phase of the project is protection of all the floodplain north of EI Camino Real, the alternatives that exceeded the project budget of approximately $35 million were further analyzed as to the cost necessary for the portions needed to meet CSC goals. That cost is also reported below. The following is a description of the conceptual alternatives analyzed: CONCEPTUAL ALTERNATIVE A Alternative Description Under conceptual alternative A, no new project elements would be implemented in the study area. Flood flows would continue to overtop channel banks and inundate adjacent properties, resulting in flood-related damages to residences and businesses. The existing concrete facilities in Permanente and Hale Creeks, and the Diversion Channel would be monitored and rebuilt as needed and current sediment removal and vegetation maintenance practices would be continued. Conceptual Alternative A is composed of CPE 1: No Project. Technical Feasibility All project elements are technically feasible with current construction techniques. Costs Capital costs would be $0. Maintenance costs would be $280,000 annually. CONCEPTUAL ALTERNATIVE B Alternative Description This alternative combines floodwall and bypass channel elements to increase the capacity of all project reaches to the design flows. Conceptual alternative B is composed of the following CPEs: Permanente Creek Flood Protection Project Page 58 Planning Study Report July 2008 CPE 7 -Hale Bypass: An underground bypass consisting of an 8••foot by 8-foot concrete box culvert would be constructed a length of approximately 3,000 feet. The bypass would be constructed under local residential roadways from a fevv hundred feet downstream of Foothill Expressway to the beginning of the concrete Hale Creek section at Rosita Avenue. CPE 8 -Permanente Bypass: An underground bypass consisting of a 10••foot by 10-foot concrete box culvert would be constructed a length of approximately 11,500 feet from Reach P8 to Reach P5. The proposed bypass culvert would begin upstream of the Permanente Diversion, follow Miramonte Avenue to Park Drive and reconnect to the Permanente Creek channel just upstream of EI Camino Real. CPE 9 - Floodwalls: Reach P2 would be modified by the addition of 5-foot to 7-foot floodwalls to the top of the existing levees. All other existing concrete U-frame channels (Reaches P3, P5, and H1) would be removed and rebuilt with floodwalls from 8 to 30 feet above adjacent ground. CPE 16 - E/ Camino Culvert: The underground box culverts between EI Camino Real and Villa Street would be enlarged by lowering the bottom of the culverts by approximately 3 to 10 feet. CPE 19 -New Diversion Structure: The existing diversion structure and 54-inch pipeline would be abandoned and replaced by a new structure. The inlet to the new structure would be along Miramonte Avenue just upstream of the current eastward bend. Anew 8-foot by 8-foot box culvert would convey the flows under Miramonte Avenue to connect with the creek at Eastwood Place. Technical Feasibility Due to the very high floodwall heights, this alternative is not considered technically feasible. Costs Capital cost for the entire alternative would be: $81,500,000. Capital cost for the portion required under CSC would be: $37,500,000. CONCEPTUAL ALTERNATIVE C Alternative Description This alternative combines floodwall and bypass channel elements to increase the capacity of all project reaches to the design flows. Conceptual alternative C is composed of the following CPEs: Permanente Creek Flood Protection Project Page 59 Planning Study Report July 2008 CPE 7 -Hale Bypass: An underground bypass consisting of an 8-foot by 8-foot concrete box culvert would be constructed a length of approximately 3,000 feet. The bypass would be constructed under local residential roadways from a few hundred feet downstream of Foothill Expressway to the beginning of the concrete Hale Creek section at Rosita Avenue. CPE 8 -Permanente Bypass: An underground bypass consisting of a 10-foot by 10-foot concrete box culvert would be constructed a length of approximately 11,500 feet from Reach P8 to Reach P5. The proposed bypass culvert would begin upstream of the Permanente Diversion, follow Miramonte Avenue to Park Drive and reconnect to the Permanente Creek channel just upstream of EI Camino Real. • CPE 9 - Floodwalls: Reach P2 would be modified by the addition of 5-foot to 7-foot floodwalls to the top of the existing levees. All other existing concrete U-frame channels (Reaches P3, P5, and H1) would be removed and rebuilt with floodwalls from 8 to 30 feet above adjacent ground. • CPE 15 - EI Camino Bypass: An underground bypass consisting of a 10-foot by 10-foot concrete box culvert would be constructed a length of approximately 4000 feet around the existing EI Camino to Villa Street culverts. The new culvert will start just south of EI Camino Real and go north and west along local streets and reconnect with the existing channel at Villa Street. • CPE 19 -New Diversion Structure: The existing diversion structure and 54-inch pipeline would be abandoned and replaced by a new structure. The inlet to the new structure would be along Miramonte Avenue just upstream of the current eastward bend. Anew 8-foot by 8-foot box culvert would convey the flows under Miramonte Avenue to connect with the creek at Eastwood Place. • CPE 18 - EI Camino Collection Channel: A new 8-foot by 8-foot box culvert would also be installed under one lane of southbound EI Camino Real. Grated inlets would be installed along EI Camino Real to allow flood waters from upstream flooding to be captured by the new culvert. Technical Feasibility Due to the very high floodwall heights, this alternative is not considered technically feasible. Costs Capital cost for the entire alternative would be: $77,000,000. Capital cost for the portion required under CSC would be: $33,000,000. CONCEPTUAL ALTERNATIVE D Alternative Description Permanente Creek Flood Protection Project Page 60 Planning Study Report July 2008 This alternative combines channel expansion and bypass elements to increase the capacity of all channel reaches to the design flows. Conceptual alternative D is composed of the following Conceptual Project Elements: • CPE 7 -Hale Bypass: An underground bypass consisting of an 8-foot by 8-foot concrete box culvert would be constructed a length of approximately 3,000 feet. The bypass would be constructed under local residential roadways from a fe~v hundred feet downstream of Foothill Expressway to the beginning of the concrete Hale Creek section at Rosita Avenue. • CPE 8 -Permanente Bypass: An underground bypass consisting of a 10-foot by 10-foot concrete box culvert would be constructed a length of approximately 11,500 feet from Reach P8 to Reach P5. The proposed bypass culvert would begin upstream of the Permanente Diversion, follow Miramonte Avenue to Park Drive and reconnect to the Permanente Creek channel just upstream of EI Camino Real. • CPE 9 - Floodwalls: Permanente Creek down-stream of Highw~~y 101 (Reach P2) would be modified by the addition of 5-foot to 7-foot floodwalls to the top of the existing levees. There would be up to 8-foot floodwalls needed in Reach P3. • CPE 10 -Channel Widening: All existing concrete U-frame channels (Reaches P3, P5, and H1) would be removed and rebuilt wider. In addition, several bridcles and culverts in the project area would be similarly modified (widened/enlarged) to contain the one-percent design flow. • CPE 16 - E/ Camino Culvert: The underground box culverts between EI Camino Real and Villa Street would be enlarged by being lowered by approximately 3 to 10 feet. • CPE 19 -New Diversion Structure: The existing diversion structure and 54-inch pipeline would be abandoned and replaced by a new structure. The inlet to the new structure would be along Miramonte Avenue just upstream of the current eastward bend. Anew 8-foot by 8-foot box culvert would convey the flows under Miramonte Avenue to connect with the creek at Eastwood Place. • CPE 18 - E/ Camino Collection Channel: A new 8-foot by 8-foot box culvert would also be installed under one lane of southbound EI Camino Real. Grated inlets would be installed along EI Camino Real to allow flood waters from upstream flooding to be captured by the new culvert. Technical Feasibility All project elements are technically feasible. The 1.I Camino Real Culvert expansion element would require some special construction techniquE~s. Costs Capital cost for the entire alternative would be: $8:?,500,000. Permanente Creek Flood Protection Project Page 61 Planning Study Report July 2008 Capital cost for the portion required under CSC would be: $39,500,000. CONCEPTUAL ALTERNATIVE E Alternative Description This alternative combines channel expansion and bypass elements to increase the capacity of all channel reaches to the design flows. Conceptual alternative E is composed of the following Conceptual Project Elements: CPE 7 -Hale Bypass: An underground bypass consisting of an 8-foot by 8-foot concrete box culvert would be constructed a length of approximately 3,000 feet. The bypass would be constructed under local residential roadways from a few hundred feet downstream of Foothill Expressway to the beginning of the concrete Hale Creek section at Rosita Avenue. CPE 8 -Permanente Bypass: An underground bypass consisting of a 10-foot by 10-foot concrete box culvert would be constructed a length of approximately 11,500 feet from Reach P8 to Reach P5. The proposed bypass culvert would begin upstream of the Permanente Diversion, follow Miramonte Avenue to Park Drive and reconnect to the Permanente Creek channel just upstream of EI Camino Real. • CPE 9 - Floodwalls: Permanente Creek down-stream of Highway 101 (Reach P2) would be modified by the addition of 5-foot to 7-foot floodwalls to the top of the existing levees. There would be up to 8-foot floodwalls needed in Reach P3. • CPE 10 -Channel Widening: All existing concrete U-frame channels (Reaches P3, P5, and H1) would be removed and rebuilt wider. In addition, several bridges and culverts in the project area would be similarly modified (widened/enlarged) to contain the one-percent design flow. • CPE 15 - E/ Camino Bypass: An underground bypass consisting of a 10-foot by 10-foot concrete box culvert would be constructed a length of approximately 4000 feet around the existing EI Camino to Villa Street culverts. The new culvert will start just south of EI Camino Real and go north and west along local streets and reconnect with the existing channel at Villa Street. • CPE 19 -New Diversion Structure: The existing diversion structure and 54-inch pipeline would be abandoned and replaced by a new structure. The inlet to the new structure would be along Miramonte Avenue just upstream of the current eastward bend. Anew 8-foot by 8-foot box culvert would convey the flows under Miramonte Avenue to connect with the creek at Eastwood Place. • CPE 18 - E/ Camino Collection Channel: A new 8-foot by 8-foot box culvert would also be installed under one lane of southbound EI Camino Real. Grated inlets would be installed along EI Camino Real to allow flood waters from upstream flooding to be captured by the new culvert. Permanente Creek Flood Protection Project Page 62 Planning Study Report July 2008 Technical Feasibility All project elements are technically feasible. Costs Capital cost for the entire alternative would be: $7!3,000,000. Capital cost for the portion required under CSC would be: $35,000,000. CONCEPTUAL ALTERNATIVE F Alternative Description This alternative combines geomorphic stream restoration and bypass elements to increase the capacity of all channel reaches to the design flows and to restore habitat values. Conceptual alternative F is composed of the following Concep~rual Project Elements: CPE 7 -Hale Bypass: An underground bypass consisting of an 8•foot by 8-foot concrete box culvert would be constructed a length of approximately 3,000 feet. The bypass would be constructed under local residential roadways from a few hundred feet downstream of Foothill Expressway to the beginning of the concrete Hale Creek section at Rosita Avenue. CPE 8 -Permanente Bypass: An underground bypass consisting of a 10•foot by 10-foot concrete box culvert would be constructed a length of approximately 11,500 feet from Reach P8 to Reach P5. The proposed bypass culvert would begin upstream of the Permanente Diversion, follow Miramonte Avenue to Park Drive and reconnect to the Permanente Creek channel just upstream of EI Camino Real. CPE 9 -Floodwalls: Permanente Creek down-stream of Highw~iy 101 (Reach P2) would be modified by the addition of 5-foot to 7-foot Floodwalls to the top of the existing levees. CPE 11-Geomorphic Stream Restorati~~n: All existing concrete U-frame channels (Reaches P3, P5, and H1) would be removed. A row of parcels next to the creek channel would be purchased and the existing improvements removed. Anew meandering natural channel with appropriate wavelength and floodplain would be built. In addition, the many bridges and culverts in these reaches would be modified; culverts would be installed under the roadways to connect the floodplain areas on either side of the bridges. CPE 19 -New Diversion Structure: The existing diversion structure and 54-inch pipeline would be abandoned and replaced by a new structure. The inlet to the new structure would be along Miramonte Avenue just upstream of the current eastward bend. Anew 8-foot by 8-foot box culvert would convey the flows under Miramonte Avenue to connect with the creek at Eastwood Place. CPE 18 - E/ Camino Collection Channel.• Permanente Creek Flood Protection Project Page 63 Planning Study Report July 2008 A new 8-foot by 8-foot box culvert would also be installed under one lane of southbound EI Camino Real. Grated inlets would be installed along EI Camino Real to allow flood waters from upstream flooding to be captured by the new culvert. Technical Feasibility All project elements are technically feasible. Some specialized design assistance may be necessary for the detailed design of the geomorphic channel. Costs Capital cost for the entire alternative would be: $146,000,000. Capital cost for the portion required under CSC would be: $73,000,000. CONCEPTUAL ALTERNATIVE G Alternative Description This alternative combines flow detention, bypass, and riparian restoration elements to reduce design flows such that existing and restored channel reaches can convey flows safely downstream. Conceptual alternative G is composed of the following Conceptual Project Elements: CPE 2 -Flow Detention South Branch Dam: A new concrete dam would be built in the far upstream reach of South Branch Permanente Creek in the Hanson Permanente Quarry. The dam would be approximately 100 feet high and 500 feet wide at the top. The~dam outlet would be open at all times such that the dam would only impound water during rainfall events that cause flows in excess of 50 cubic feet per second (cfs). CPE 3 -Flow Detention Rancho San Antonio: An off-stream detention facility would be created on a parcel owned by the County of Santa Clara Parks Department next to the Rancho San Antonio County Park. The average depth of the approximately 5 acre detention facility would be 15 feet, producing approximately 75 acre-feet of storage volume. The site would be contoured to resemble natural relief. CPE 5 -Flow Detention McKelvey Park: An off-stream detention facility would be created on the current baseball fields at McKelvey Park in the city of Mountain View. The average depth of the approximately 5 acre detention facility would be approximately 13 feet, producing approximately 60 acre-feet of storage volume. CPE 7 -Hale Bypass: An underground bypass consisting of an 8-foot by 8-foot concrete box culvert would be constructed a length of approximately 3,000 feet. The bypass would be constructed under local residential roadways from a few hundred feet downstream of Foothill Expressway to the beginning of the concrete Hale Creek section at Rosita Avenue. CPE 9 - Floodwalls: Permanente Creek Flood Protection Project Page 64 Planning Study Report July 2008 Downstream of Highway 101 along Reach P2 would be modified by the addition of 1-foot to 3-foot high concrete floodwalls to the levee channels. CPE 12 -Riparian Restoration: The existing concrete channel in reaches F'3 and P5 would be replaced with an earth channel with riparian vegetation. The channel invert may require rock lining, based on velocity parameters. CPE 17 -Hale Improvement: The existing concrete channel in reach H1 would be improved by lowering the bottom of the channel and removing drop structures writhin the existing District right-of-way. This would improve the capacity of the reach to the full design flow. CPE 19 -New Diversion Structure: The existing diversion structure and 54-inch pipeline would be abandoned and replaced by a new structure. The inlet to the new structure would be along Miramonte Avenue just upstream of the current eastward bend. Anew 8-foot by 8-foot box culvert would convey the flows under Miramonte Avenue to connect with the creek at Eastwood Place. Technical Feasibility All project elements are technically feasible. Costs Capital cost for the entire alternative would be: $2Ei,000,000. CONCEPTUAL ALTERNATIVE H Alternative Description This alternative combines flow detention, diversion, and riparian restoration elements to reduce design flows such that existing and restored channel reaches can convey flows safely downstream. Conceptual alternative H is composed of the following Conceptual Project Elements: CPE 4 -Flow Detention Grant Road: Fifteen acres of the Grant Road farm parcE~l site would be cleared and excavated to a depth of 20 feet, producing approximately 300 acre-feet of storage volume. Anew 10- foot by 10-foot culvert would convey flows sander Grant Road to connect the farm parcel to the Permanente Diversion. The existing Permanente Diversion concrete channel would be improved to carry the full flood flows to Grant Road. CPE 6 -Hale Diversion: An underground diversion channel consisting of an 8-foot by 8-foot concrete box culvert would be constructed a length of approxim~~tely 4,000 feet. The diversion would be constructed under local residential roadwa~rs from a few hundred feet downstream of Foothill Expressway to the just upstream of the Permanente Diversion channel. CPE 9 - Floodwalls: Permanente Creek Flood Protection Project Page 65 Planning Study Report July 2008 Downstream of Highway 101 along Reach P2 would be modified by the addition of 1-foot to 3-foot high concrete floodwalls to the levee channels. CPE 12 -Riparian Restoration: The existing concrete channel in reaches P3 and P5 would be replaced with an earth channel with riparian vegetation. The channel invert may require rock lining, based on velocity parameters. CPE 19 -New Diversion Structure: The existing diversion structure and 54-inch pipeline would be abandoned and replaced by a new structure. The inlet to the new structure would be along Miramonte Avenue just upstream of the current eastward bend. Anew 8-foot by 8-foot box culvert would convey the flows under Miramonte Avenue to connect with the creek at Eastwood Place. Technical Feasibility All project elements are technically feasible. Costs Capital cost for the entire alternative would be: $51,000,000. CONCEPTUAL ALTERNATIVE 1 Alternative Description This alternative combines flow detention, bypass, and riparian restoration elements to reduce design flows such that existing and restored channel reaches can convey flows safely downstream. Conceptual alternative I is composed of the following Conceptual Project Elements: • CPE 2 -Flow Detention South Branch Dam: A new concrete dam would be built in the far upstream reach of South Branch Permanente Creek in the Hanson Permanente Quarry. The dam would be approximately 100 feet high and 500 feet wide at the top. The dam outlet would be open at all times such that the dam would only impound water during rainfall events that cause flows in excess of 50 cubic feet per second. CPE 4 -Flow Detention Grant Road: Three acres of the Grant Road farm parcel site would be cleared and excavated to a depth of 20 feet, producing approximately 60 acre-feet of storage volume. Anew 10-foot by 10-foot culvert would convey flows under Grant Road to connect the farm parcel to the Permanente Diversion. The existing Permanente Diversion concrete channel would be improved to carry the full flood flows to Grant Road. CPE 5 -Flow Detention McKelvey Park: An off-stream detention facility would be created on the current baseball fields at McKelvey Park in the city of Mountain View. The average depth of the approximately 5 acre detention facility would be approximately 13 feet, producing approximately 60 acre-feet of storage volume. Permanente Creek Flood Protection Project Page 66 Planning Study Report July 2008 • CPE 7 -- Hale Bypass: An underground bypass consisting of an 8-foot by 8-foot concrete box culvert would be constructed a length of approximately 3,000 feet. The bypass would be constructed under local residential roadways from a fevv hundred feet downstream of Foothill Expressway to the beginning of the concrete Hale Creek section at Rosita Avenue. • CPE 9 - Floodwalls: Downstream of Highway 101 along Reach P2 would be modified by the addition of 1-foot to 3-foot high concrete floodwalls to the levee channels. • CPE 12 -Riparian Restoration: The existing concrete channel in reaches F'3 and P5 would be replaced with an earth channel with riparian vegetation. The channel invert may require rock lining, based on velocity parameters. • CPE 17 -Hale Improvement: The existing concrete channel in reach H1 would be improved by lowering the bottom of the channel and removing drop structures ~nrithin the existing District right-of-way. This would improve the capacity of the reach to the full design flow. • CPE 19 -New Diversion Structure: The existing diversion structure and 54-inch pipeline would be abandoned and replaced by a new structure. The inlet to the new st~~ucture would be along Miramonte Avenue just upstream of the current eastward bend. Anew 8-foot by 8-foot box culvert would convey the flows under Miramonte Avenue to connect with the creek at Eastwood Place. Technical Feasibility All project elements are technically feasible. Costs Capital cost for the entire alternative would be: $3:1,000,000. CONCEPTUAL ALTERNATIVE J Alternative Description This alternative combines flow detention, bypass, ,end riparian restoration elements to reduce design flows such that existing and restored channel reaches can convey flows safely downstream. Conceptual alternative J is composE~d of the following Conceptual Project Elements: CPE 3 -Flow Detention Rancho San Antonio: An off-stream detention facility would be created on a parcel owned by the County of Santa Clara Parks Department next to the Rancho San Antonio County Park. The average depth of the approximately 5 acre detention facility would be 15 feet, producing approximately 75 acre-feet of storage volurne. The site would be contoured to resemble natural relief. Permanente Creek Flood Protection Project Page 67 Planning Study Report July 2008 CPE 4 -Flow Detention Grant Road: Three acres of the Grant Road farm parcel site would be cleared and excavated to a depth of 20 feet, producing approximately 60 acre-feet of storage volume. Anew 10-foot by 10-foot culvert would convey flows under Grant Road to connect the farm parcel to the Permanente Diversion. The existing Permanente Diversion concrete channel would be improved to carry the full flood flows to Grant Road. • CPE 5 -Flow Detention McKelvey Park: An off-stream detention facility would be created on the current baseball fields at McKelvey Park in the city of Mountain View. The average depth of the approximately 5 acre detention facility would be approximately 13 feet, producing approximately 60 acre-feet of storage volume. • CPE 7 -Hale Bypass: An underground bypass consisting of an 8-foot by 8-foot concrete box culvert would be constructed a length of approximately 3,000 feet. The bypass would be constructed under local residential roadways from a few hundred feet downstream of Foothill Expressway to the beginning of the concrete Hale Creek section at Rosita Avenue. • CPE 9 - Floodwalls: Downstream of Highway 101 along Reach P2 would be modified by the addition of 1-foot to 3-foot high concrete floodwalls to the levee channels. • CPE 12 -Riparian Restoration: The existing concrete channel in reaches P3 and P5 would be replaced with an earth channel with riparian vegetation. The channel invert may require rock lining, based on velocity parameters. • CPE 17 -Hale Improvement: The existing concrete channel in reach H1 would be improved by lowering the bottom of the channel and removing drop structures within the existing District right-of-way. This would improve the capacity of the reach to the full design flow. • CPE 19 -New Diversion Structure: The existing diversion structure and 54-inch pipeline would be abandoned and replaced by a new structure. The inlet to the new structure would be along Miramonte Avenue just upstream of the current eastward bend. Anew 8-foot by 8-foot box culvert would convey the flows under Miramonte Avenue to connect with the creek at Eastwood Place. Technical Feasibility All project elements are technically feasible. Costs Capital cost for the entire alternative would be: $35,000,000. Permanente Creek Flood Protection Project Page 68 Planning Study Report July 2008 CONCEPTUAL ALTERNATIVE K Alternative Description This alternative combines flow detention, diversion, and riparian restoration elements to reduce design flows such that existing and restored channel reaches can convey flows safely downstream. Conceptual alternative K is composted of the following Conceptual Project Elements: CPE 2 -Flow Detention South Branch Gram: A new concrete dam would be built in the f,~r upstream reach of South Branch Permanente Creek in the Hanson Permanf~nte Quarry. The dam would be approximately 100 feet high and 500 feet ~ntide at the top. The dam outlet would be open at all times such that the dam would only impound water during rainfall events that cause flows in excess of 50 cubic feet per second. CPE 3 -Flow Detention Rancho San Antonio: An off-stream detention facility would be created on a parcel owned by the County of Santa Clara Parks Department next to the Rancho San Antonio County Park. The average depth of the approximately 5 acre detention facility would be 15 feet, producing approximately 75 acre-feet of storage volurne. The site would be contoured to resemble natural relief. CPE 4 -Flow Detention Grant Road: 2.5 acres of the Grant Road farm parcel site would be cleared and excavated to a depth of 20 feet, producing approximately 50 acrE~-feet of storage volume. Anew 10-foot by 10-foot culvert would convey flows under Grant Road to connect the farm parcel to the Permanente Diversion. The existing Perm~~nente Diversion concrete channel would be improved to carry the full flood flows to Grant Road. • CPE 6 -Hale Diversion: An underground diversion channel consisting of an 8-foot by 8-foot concrete box culvert would be constructed a length of approxim~~tely 4,000 feet. The diversion would be constructed under local residential roadwa~~s from a few hundred feet downstream of Foothill Expressway to the just upstream o1 the Permanente Diversion channel. • CPE 9 - F/oodwalls: Downstream of Highway 101 along Reach P2 would be modified by the addition of 1-foot to 3-foot high concrete floodwalls to the levee channels. • CPE 12 -Riparian Restoration: The existing concrete channel in reaches P3 and P5 would be replaced with an earth channel with riparian vegetation. The channel invert may require rock lining, based on velocity parameters. • CPE 19 -New Diversion Structure: The existing diversion structure and 54-inch pipeline would be abandoned and replaced by a new structure. The inlet to the new structure would be along Miramonte Avenue just upstream of the current eastward bend. Anew 8-foot by 8-foot box culvert would convey the flows under Miramonte Avenue to connect with the creek at Eastwood Place. Permanente Creek Flood Protection Project Page 69 Planning Study Report July 2008 Technical Feasibility All project elements are technically feasible. Costs Capital cost for the entire alternative would be: $30,500,000. CONCEPTUAL ALTERNATIVE L Alternative Description This alternative combines flow detention, diversion, and riparian restoration elements to reduce design flows such that existing and restored channel reaches can convey flows safely downstream. Conceptual Alternative L is composed of the following Conceptual Project Elements: CPE 2 -Flow Detention South Branch Dam: A new concrete dam would be built in the far upstream reach of South Branch Permanente Creek in the Hanson Permanente Quarry. The dam would be approximately 100 feet high and 500 feet wide at the top. The dam outlet would be open at all times such that the dam would only impound water during rainfall events that cause flows in excess of 50 cubic feet per second. CPE 4 -Flow Detention Grant Road: Six acres of the Grant Road farm parcel site would be cleared and excavated to a depth of 20 feet, producing approximately 120 acre-feet of storage volume. Anew 10-foot by 10-foot culvert would convey flows under Grant Road to connect the farm parcel to the Permanente Diversion. The existing Permanente Diversion concrete channel would be improved to carry the full flood flows to Grant Road. • CPE 6 -Hale Diversion: An underground diversion channel consisting of an 8-foot by 8-foot concrete box culvert would be constructed a length of approximately 4,000 feet. The diversion would be constructed under local residential roadways from a few hundred feet downstream of Foothill Expressway to the just upstream of the Permanente Diversion channel. • CPE 9 - Floodwalls: Downstream of Highway 101 along Reach P2 would be modified by the addition of 1-foot to 3-foot high concrete floodwalls to the levee channels. • CPE 12 -Riparian Restoration: The existing concrete channel in reaches P3 and P5 would be replaced with an earth channel with riparian vegetation. The channel invert may require rock lining, based on velocity parameters. • CPE 19 -New Diversion Structure: The existing diversion structure and 54-inch pipeline would be abandoned and replaced by a new structure. The inlet to the new structure would be along Miramonte Avenue Permanente Creek Flood Protection Project Page 70 Planning Study Report July 2008 just upstream of the current eastward bend. Anew 8-foot by 8-foot box culvert would convey the flows under Miramonte Avenue to connect with the creek at Eastwood Place. Technical Feasibility All project elements are technically feasible. Costs Capital cost for the entire alternative would be: $35,000,000. CONCEPTUAL ALTERNATIVE M Alternative Description This alternative combines flow detention, diversion, and riparian restoration elements to reduce design flows such that existing and restored channel reaches can convey flows safely downstream. Conceptual alternative M is composed of the following Conceptual Project Elements: CPE 3 -Flow Detention Rancho San Antonio: An off-stream detention facility would be created on a parcel owned by the County of Santa Clara Parks Department next to the Rancho San Antonio County Park. The average depth of the approximately 5 acre detention facility would be 15 feet, producing approximately 75 acre-feet of storage volume. The site would be contoured to resemble natural relief. CPE 4 -Flow Detention Grant Road: Six acres of the Grant Road farm parcel sii:e would be cleared and excavated to a depth of 20 feet, producing approximately 120 acre-feet of storage volume. Anew 10-foot by 10-foot culvert would convey flows under Carant Road to connect the farm parcel to the Permanente Diversion. The existing Permanente Diversion concrete channel would be improved to carry the full flood flows to Gr~int Road. • CPE 6 -Hale Diversion: An underground diversion channel consisting of an 8-foot by 8-foot concrete box culvert would be constructed a length of approximately 4,000 feet. The diversion would be constructed under local residential roadways from a few hundred feet downstream of Foothill Expressway to the just upstream of the Permanente Diversion channel. • CPE 9 - F/oodwalls: Downstream of Highway 101 along Reach P2 would be modified by the addition of 1-foot to 3-foot high concrete floodwalls to the levee channels. • CPE 12 -Riparian Restoration: The existing concrete channel in reaches F'3 and P5 would be replaced with an earth channel with riparian vegetation. The channel invert may require rock lining, based on velocity parameters. • CPE 19 -New Diversion Structure: Permanente Creek Flood Protection Project Page 71 Planning Study Report July 2008 The existing diversion structure and 54-inch pipeline would be abandoned and replaced by a new structure. The inlet to the new structure would be along Miramonte Avenue just upstream of the current eastward bend. Anew 8-foot by 8-foot box culvert would convey the flows under Miramonte Avenue to connect with the creek at Eastwood Place. Technical Feasibility All project elements are technically feasible. Costs Capital cost for the entire alternative would be: $35,000,000. CONCEPTUAL ALTERNATIVE N Alternative Description This alternative combines flow detention, bypass, and riparian restoration elements to reduce design flows such that existing and restored channel reaches can convey flows safely downstream. Conceptual alternative N is composed of the following Conceptual Project Elements: CPE 2 -Flow Detention South Branch Dam: A new concrete dam would be built in the far upstream reach of South Branch Permanente Creek in the Hanson Permanente Quarry. The dam would be approximately 100 feet high and 500 feet wide at the top. The dam outlet would be open at all times such that the dam would only impound water during rainfall events that cause flows in excess of 50 cubic feet per second. CPE 3 -Flow Detention Rancho San Antonio: An off-stream detention facility would be created on a parcel owned by the County of Santa Clara Parks Department next to the Rancho San Antonio County Park. The average depth of the approximately 5 acre detention facility would be 15 feet, producing approximately 75 acre-feet of storage volume. The site would be contoured to resemble natural relief. CPE 7 -Hale Bypass: An underground bypass consisting of an 8-foot by 8-foot concrete box culvert would be constructed a length of approximately 3,000 feet. The bypass would be constructed under local residential roadways from a few hundred feet downstream of Foothill Expressway to the beginning of the concrete Hale Creek section at Rosita Avenue. CPE 9 - F/oodwalls: Downstream of Highway 101 along Reach P2 would be modified by the addition of 1-foot to 3-foot high concrete floodwalls to the levee channels. CPE 12 -Riparian Restoration: The existing concrete channel in reaches P3 and P5 would be replaced with an earth channel with riparian vegetation. The channel invert may require rock lining, based on velocity parameters. Permanente Creek Flood Protection Project Page 72 Planning Study Report July 2008 CPE 14 -Flow Detention 7`n Day Advernrist Church: An off-stream detention facility would be created on the back lot of the Seventh Day Adventist Church property on Springer Ro<~d. The back parcel is approximately 1.7 acres in size. The average depth would be approximately 10 feet, producing approximately 17 acre-feet of storage volui~ne. The existing house on the parcel would have to be replaced with an equivalent house in the neighborhood. CPE 17 -Hale Improvement: The existing concrete channel in reach H1 would be improved by lowering the bottom of the channel and removing drop structures within the existing District right-of-way. This would improve the capacity of the reach to the full design flow. CPE 19 -New Diversion Structure: The existing diversion structure and 54-inch pipeline would be abandoned and replaced by a new structure. The inlet to the new structure would be along Miramonte Avenue just upstream of the current eastward bend. Anew 8-foot by 8-foot box culvert would convey the flows under Miramonte AvenuE~ to connect with the creek at Eastwood Place. Technical Feasibility All project elements are technically feasible. Costs Capital cost for the entire alternative would be: $24,500,000. CONCEPTUAL ALTERNATIVE O Alternative Description This alternative combines flow detention, bypass, and riparian restoration elements to reduce design flows such that existing and restored channel reaches can convey flows safely downstream. Conceptual alternative O is composed of the following Conceptual Project Elements: CPE 2 -Flow Detention South Branch Dam: A new concrete dam would be built in the far upstream reach of South Branch Permanente Creek in the Hanson Permarn~nte Quarry. The dam would be approximately 100 feet high and 500 feet vvide at the top. The dam outlet would be open at all times such that the dam would only irnpound water during rainfall events that cause flows in excess of 50 cubic feet per second. CPE 3 -Flow Detention Rancho San Antonio: An off-stream detention facility would be created on a parcel owned by the County of Santa Clara Parks Department next to the Rancho San Antonio County Park. The average depth of the approximately 5 acre detention facility would be 15 feet, producing approximately 75 acre-feet of storage volui~ne. The site would be contoured to resemble natural relief. CPE 7 -Hale Bypass: Permanente Creek Flood Protection Project Page 73 Planning Study Report July 2008 An underground bypass consisting of an 8-foot by 8-foot concrete box culvert would be constructed a length of approximately 3,000 feet. The bypass would be constructed under local residential roadways from a few hundred feet downstream of Foothill Expressway to the beginning of the concrete Hale Creek section at Rosita Avenue. CPE 9 - Floodwalls: Downstream of Highway 101 along Reach P2 would be modified by the addition of 1-foot to 3-foot high concrete floodwalls to the levee channels. CPE 12 -Riparian Restoration: The existing concrete channel in reaches P3 and P5 would be replaced with an earth channel with riparian vegetation. The channel invert may require rock lining, based on velocity parameters. CPE 14 -Flow Detention 7`h Day Adventist Church: An off-stream detention facility would be created on the back lot of the Seventh Day Adventist Church property on Springer Road. The back parcel is approximately 1.7 acres in size. The average depth would be approximately 10 feet, producing approximately 17 acre-feet of storage volume. The existing house on the parcel would have to be replaced with an equivalent house in the neighborhood. CPE 19 -New Diversion Structure: The existing diversion structure and 54-inch pipeline would be abandoned and replaced by a new structure. The inlet to the new structure would be along Miramonte Avenue just upstream of the current eastward bend. Anew 8-foot by 8-foot box culvert would convey the flows under Miramonte Avenue to connect with the creek at Eastwood Place. Technical Feasibility All project elements are technically feasible. Costs Capital cost for the entire alternative would be: $26,000,000. CONCEPTUAL ALTERNATIVE P Alternative Description This alternative combines flow detention, bypass, and riparian restoration elements to reduce design flows such that existing and restored channel reaches can convey flows safely downstream. Conceptual alternative P is composed of the following Conceptual Project Elements: CPE 4 -Flow Detention Granf Road: Ten acres of the Grant Road farm parcel site would be cleared and excavated to a depth of 20 feet, producing approximately 200 acre-feet of storage volume. Anew 10-foot by 10-foot culvert would convey flows under Grant Road to connect the farm parcel to the Permanente Diversion. The existing Permanente Diversion concrete channel would be improved to carry the full flood flows to Grant Road. Permanente Creek Flood Protection Project Page 74 Planning Study Report July 2008 • CPE 7 -Hale Bypass: An underground bypass consisting of an 8-foot by 8-foot concrete box culvert would be constructed a length of approximately 3,000 feet. The bypass would be constructed under local residential roadways from a fev/ hundred feet downstream of Foothill Expressway to the beginning of the concrete Hale Creek section at Rosita Avenue. • CPE 9 - Floodwalls: Downstream of Highway 101 along Reach P2 would be modified by the addition of 1-foot to 3-foot high concrete floodwalls to the levee channels. • CPE 12 -Riparian Restoration: The existing concrete channel in reaches F'3 and P5 would be replaced with an earth channel with riparian vegetation. The channel invert may require rock lining, based on velocity parameters. • CPE 14 -Flow Detention 7rh Day Adveni~ist Church: An off-stream detention facility would be created on the back lot of the 7th Day Adventist Church property on Springer Road. The beck parcel is approximately 1.7 acres in size. The average depth would be approximately 10 feet, producing approximately 17 acre-feet of storage volume. The existing house on the parcel would have to be replaced with an equivalent house in the nE~ighborhood. • CPE 17 -Hale Improvement: The existing concrete channel in reach H1 would be improved by lowering the bottom of the channel and removing drop structures within the existing District right-of-way. This would improve the capacity of the reach to the full design flow. • CPE 19 -New Diversion Structure: The existing diversion structure and 54-inch pipeline would be abandoned and replaced by a new structure. The inlet to the new structure would be along Miramonte Avenue just upstream of the current eastward bend. Anew 8-foot by 8-foot box culvert would convey the flows under Miramonte Avenue to connect with the creek at Eastwood Place. Technical Feasibility All project elements are technically feasible. Costs Capital cost for the entire alternative would be: $4:5,500,000. CONCEPTUAL ALTERNATIVE Q Alternative Description This alternative uses flood-proofing elements to protect the properties in the floodplain from damages during flood events. Conceptual alternative Q is composed of the following Conceptual Project Element: • CPE 13 -Non-Structural (F/oodproofing): Permanente Creek Flood Protection Project Page 75 Planning Study Report July 2008 The 2,778 parcels in the one-percent floodplain would be protected by either of two means: structural elevation or flood shielding. Structural elevation would be achieved by raising parcel improvements (actual house structures) above the flood elevation and placing them on new foundations. Flood shielding would protect parcels by surrounding the perimeters of properties with water proof shielding to an elevation higher than the flood elevation. Technical Feasibility This project element is technically feasible with current construction techniques. Costs Capital costs would be $112,500,000. Capital costs for the CSC portion would be $66,500,000. CONCEPTUAL ALTERNATIVE R This alternative involved work with the First Baptist Church of Los Altos. The right-of-way required by the alternative was not available; therefore, the alternative was removed from further consideration. CONCEPTUAL ALTERNATIVE S Alternative Description This alternative combines flow detention, bypass, and riparian restoration elements to reduce design flows such that existing and restored channel reaches can convey flows safely downstream. Conceptual alternative S is composed of the following Conceptual Project Elements: • CPE 3 -Flow Detention Rancho San Antonio: An off-stream detention facility would be created on a parcel owned by the County of Santa Clara Parks Department next to the Rancho San Antonio County Park. The average depth of the approximately 5 acre detention facility would be 15 feet, producing approximately 75 acre-feet of storage volume. The site would be contoured to resemble natural relief. CPE 5 -Flow Detention McKelvey Park: An off-stream detention facility would be created on the current baseball fields at McKelvey Park in the city of Mountain View. The average depth of the approximately 5 acre detention facility would be approximately 13 feet, producing approximately 60 acre-feet of storage volume. CPE 7 -Hale Bypass: An underground bypass consisting of an 8-foot by 8-foot concrete box culvert would be constructed a length of approximately 3,000 feet. The bypass would be constructed under local residential roadways from a few hundred feet downstream of Foothill Expressway to the beginning of the concrete Hate Creek section at Rosita Avenue. CPE 8 -Permanente Bypass: Permanente Creek Flood Protection Project Page 76 Planning Study Report July 2008 An underground bypass consisting of a 8-foot by 6-foot diameter box culvert would be constructed a length of approximately 220() feet from the St. Francis School bridge to the Cuesta Park Annex under Miramonte Avenue and Cuesta Drive. • CPE 9 - Floodwalls: Downstream of Highway 101 along Reach P2 would be modified by the addition of 1-foot to 3-foot high concrete floodwalls to the levee channels. • CPE 12 -Riparian Restoration: The existing concrete channel in reaches F'3 and P5 would be replaced with an earth channel with riparian vegetation. The channel invert may require rock lining, based on velocity parameters. • CPE 17 -Hale Improvement: The existing concrete channel in reach H1 would be improved by lowering the bottom of the channel and removing drop structures ~~rithin the existing District right-of-way. This would improve the capacity of the reach to the full design flow. • CPE 19 -New Diversion Structure: The existing diversion structure and 54-inch pipeline would be abandoned and replaced by a new structure. The inlet to the new structure would be along Miramonte Avenue just upstream of the current eastward bencl. Anew 8-foot by 8-foot box culvert would convey the flows under Miramonte Avenue to connect with the creek at Eastwood Place. • CPE 20 -Flood Detention Cuesta Park i~nnex: A flood detention facility would be created ~~n the Cuesta Park Annex property of the City of Mountain View. The average depth of the 12-acre facility would be 15 feet, producing approximately 130 acre-feet of storage volume. 10-year or higher flow events would be routed to the facility. A 36-inch outlet pipe would drain the stored volume back to the creek, once the peak flows would pass. Technical Feasibility This project element is technically feasible with current construction techniques. Costs Capital costs would be $60,000,000. Capital costs for the CSC portion would be $36,000,000. CONCEPTUAL ALTERNATIVE T Alternative Description This alternative combines flow detention, bypass, ;end riparian restoration elements to reduce design flows such that existing and restored channel reaches can convey flows safely downstream. Conceptual alternative T is composE~d of the following Conceptual Project Elements: • CPE 5 -Flow Detention McKelvey Park: Permanente Creek Flood Protection Project Page 77 Planning Study Report July 2008 An off-stream detention facility would be created on the current baseball fields at McKelvey Park in the city of Mountain View. The average depth of the approximately 5 acre detention facility would be approximately 13 feet, producing approximately 60 acre-feet of storage volume. CPE 7 -Hale Bypass: An underground bypass consisting of an 8-foot by 8-foot concrete box culvert would be constructed a length of approximately 3,000 feet. The bypass would be constructed under local residential roadways from a few hundred feet downstream of Foothill Expressway to the beginning of the concrete Hale Creek section at Rosita Avenue. CPE 8 -Permanente Bypass: This bypass would consist of two different sizes. The upstream portion would be an 8-foot by 7-foot box culvert bypass channel from Eastwood Drive to St. Francis School. The downstream portion would consist of a 12-foot by 7-foor box culvert from the school to Cuesta Park Annex. The channel along Reach P8 from the Diversion to Portland Avenue would also have to be improved by replacing the concrete channel. • CPE 9 - F/oodwalls: Downstream of Highway 101 along Reach P2 would be modified by the addition of 1-foot to 3-foot high concrete floodwalls to the levee channels. • CPE 12 -Riparian Restoration: The existing concrete channel in reaches P3 and P5 would be replaced with an earth channel with riparian vegetation. The channel invert may require rock lining, based on velocity parameters. • CPE 17 -Hale Improvement: The existing concrete channel in reach H1 would be improved by lowering the bottom of the channel and removing drop structures within the existing District right-of-way. This would improve the capacity of the reach to the full design flow. • CPE 19 -New Diversion Structure: The existing diversion structure and 54-inch pipeline would be abandoned and replaced by a new structure. The inlet to the new structure would be along Miramonte Avenue just upstream of the current eastward bend. Anew 8-foot by.8-foot box culvert would convey the flows under Miramonte Avenue to connect with the creek at Eastwood Place. • CPE 20 -Flood Detention Cuesta Park Annex: A flood detention facility would be created on the Cuesta Park Annex property of the City of Mountain View. The average depth of the 12-acre facility would be 15 feet, producing approximately 130 acre-feet of storage volume. Ten-years or higher flow events would be routed to the facility. A 36-inch outlet pipe would drain the stored volume back to the creek, once the peak flows would pass. Technical Feasibility All project elements are technically feasible. Costs Permanente Creek Flood Protection Project Page 78 Planning Study Report July 2008 Capital costs would be $60,000,000. Capital costs for the CSC portion would be $26,000,000. CONCEPTUAL ALTERNATIVE U Alternative Description This alternative combines structural improvement, flow detention, and bypass elements to meet the project goals. Conceptual alternative U is composed of the following Conceptual Project Elements: CPE 2 -Flow Detention South Branch L1am: A new concrete dam would be built in the far upstream reach of South Branch Permanente Creek in the Hanson PermanE~nte Quarry. The dam would be approximately 100 feet high and 500 feet vride at the top. The dam outlet would be open at all times such that the dam would only irnpound water during rainfall events that cause flows in excess of 50 cubic feet per seconcl (cfs). CPE 3 -Flow Detention Rancho San Antonio: An off-stream detention facility would be created on a parcel owned by the County of Santa Clara Parks Department next to the Rancho San Antonio County Park. The average depth of the approximately 5 acre detention facility would be 15 feet, producing approximately 75 acre-feet of storage volume. The site would be contoured to resemble natural relief. • CPE 7 -Hale Bypass: An underground bypass consisting of an 8•~foot by 8-foot concrete box culvert would be constructed a length of approximately 3,000 feet. The bypass would be constructed under local residential roadways from a fevv hundred feet downstream of Foothill Expressway to the beginning of the concrete Hale Creek section at Rosita Avenue. • CPE 9 - Floodwalls: Downstream of Highway 101 along Reach P2 would be modified by the addition of 3-foot to 4-foot high concrete floodwalls to the levee channels. • CPE 10 -Channel Widening: The existing concrete channel in reaches F'3, P5, and H1 would be replaced with a larger concrete channel. In addition, several bridges along these reaches would need to be removed and replaced by larger structu~~es. • CPE 19 -New Diversion Structure: The existing diversion structure and 54-inch pipeline would be abandoned and replaced by a new structure. The inlet to the new structure would be along Miramonte Avenue just upstream of the current eastward bend. Anew 8-foot by 8-foot box culvert would convey the flows under Miramonte Avenue to connect with the creek at Eastwood Place. Technical Feasibility All project elements are technically feasible. Permanente Creek Flood Protection Project Page 79 Planning Study Report July 2008 Costs Capital cost for the entire alternative would be: $62,000,000. Capital costs for the CSC portion would be $46,000,000. CONCEPTUAL ALTERNATIVE V Alternative Description This alternative combines flow detention, bypass, and riparian restoration elements to reduce design flows such that existing and restored channel reaches can convey flows safely downstream. Conceptual alternative V is composed of the following Conceptual Project Elements: CPE 2 -Flow Detention South Branch Dam: A new concrete dam would be built in the far upstream reach of South Branch Permanente Creek in the Hanson Permanente Quarry. The dam would be approximately 100 feet high and 500 feet wide at the top. The dam outlet would be open at all times such that the dam would only impound water during rainfall events that cause flows in excess of 50 cubic feet per second (cfs). CPE 3 -Flow Detention Rancho San Antonio: An off-stream detention facility would be created on a parcel owned by the County of Santa Clara Parks Department next to the Rancho San Antonio County Park. The average depth of the approximately 5 acre detention facility would be 15 feet, producing approximately 75 acre-feet of storage volume. The site would be contoured to resemble natural relief. CPE 7 -Hale Bypass: An underground bypass consisting of an 8-foot by 8-foot concrete box culvert would be constructed a length of approximately 3,000 feet. The bypass would be constructed under local residential roadways from a few hundred feet downstream of Foothill Expressway to the beginning of the concrete Hale Creek section at Rosita Avenue. For this alternative, Hale Bypass would be extended for an additional 4400 feet along Cuesta Drive to Cuesta Park Annex. CPE 9 - F/oodwalls: Downstream of Highway 101 along Reach P2 would be modified by the addition of 1-foot to 3-foot high concrete floodwalls to the levee channels. CPE 12 -Riparian Restoration: The existing concrete channel in reaches P3 and P5 would be replaced with an earth channel with riparian vegetation. The channel invert may require rock lining, based on velocity parameters. CPE 19 -New Diversion Structure: The existing diversion structure and 54-inch pipeline would be abandoned and replaced by a new structure. The inlet to the new structure would be along Miramonte Avenue Permanente Creek Flood Protection Project Page 80 Planning Study Report July 2008 just upstream of the current eastward bend. Anew 8-foot by 8-foot box culvert would convey the flows under Miramonte Avenue to connect with the creek at Eastwood Place. CPE 20 -Flood Detention Cuesta Park i~nnex: A flood detention facility would be created ~~n the Cuesta Park Annex property of the City of Mountain View. The average depth of the 6-acre facility would be 10 feet, producing approximately 60 acre-feet of storage volume. 10-year or higher flow events would be routed to the facility. A 24-inch outlet pipe would drain the stored volume back to the creek, once the peak flows would pass. Technical Feasibility All project elements are technically feasible. Costs Capital cost for the entire alternative would be: $5!5,000,000. Capital costs for the CSC portion would be $33,000,000. CONCEPTUAL ALTERNATIVE W Alternative Description This alternative combines flow detention, bypass, and riparian restoration elements to reduce design flows such that existing and restored channel reaches can convey flows safely downstream. Conceptual alternative W is composed of the following Conceptual Project Elements: CPE 2 -Flow Detention South Branch Liam: A new concrete dam would be built in the far upstream reach of South Branch Permanente Creek in the Hanson PermanE~nte Quarry. The dam would be approximately 100 feet high and 500 feet wiide at the top. The dam outlet would be open at all times such that the dam would only irnpound water during rainfall events that cause flows in excess of 50 cubic feet per second (cfs). CPE 5 -Flow Detention McKelvey Park: An off-stream detention facility would be created on the current baseball fields at McKelvey Park in the city of Mountain Viewr. The average depth of the approximately 5 acre detention facility would be approximately 13 feet, producing approximately 60 acre-feet of storage volume. CPE 7 -Hale Bypass: An underground bypass consisting of an 8-foot by 8-foot concrete box culvert would be constructed a length of approximately 3,000 feet. The bypass would be constructed under local residential roadways from a few hundred feet downstream of Foothill Expressway to the beginning of the concrete Hale Creek section at Rosita Avenue. CPE 8 -Permanente Bypass: This bypass would consist of two different :sizes. The upstream portion would be a 54-inch pipe culvert bypass channel from Eastwood Drive to St. Francis School. The downstream portion would consist of an 8-loot by 6-foor box culvert from the school to Permanente Creek Flood Protection Project Page 81 Planning Study Report July 2008 Cuesta Park Annex. The channel along Reach P8 from the Diversion to Portland Avenue would also have to be improved by replacing the concrete channel. • CPE 9 - Floodwalls: Downstream of Highway 101 along Reach P2 would be modified by the addition of 1-foot to 3-foot high concrete floodwalls to the levee channels. • CPE 12 -Riparian Restoration: The existing concrete channel in reaches P3 and P5 would be replaced with an earth channel with riparian vegetation. The channel invert may require rock lining, based on velocity parameters. • CPE 17 -Hale Improvement: The existing concrete channel in reach H1 would be improved by lowering the bottom of the channel and removing drop structures within the existing District right-of-way. This would improve the capacity of the reach to the full design flow. • CPE 19 -New Diversion Structure: The existing diversion structure and 54-inch pipeline would be abandoned and replaced by a new structure. The inlet to the new structure would be along Miramonte Avenue just upstream of the current eastward bend. Anew 8-foot by 8-foot box culvert would convey the flows under Miramonte Avenue to connect with the creek at Eastwood Place. • CPE 20 -Flood Detention Cuesta Park Annex: A flood detention facility would be created on the Cuesta Park Annex property of the City of Mountain View. The average depth of the 7-acre facility would be 10 feet, producing approximately 70 acre-feet of storage volume. 10-year or higher flow events would be routed to the facility. A 24-inch outlet pipe would drain the stored volume back to the creek, once the peak flows would pass. Technical Feasibility All project elements are technically feasible. Costs Capital costs would be $58,000,000. Capital costs for the CSC portion would be $26,000,000. CONCEPTUAL ALTERNATIVE X Alternative Description This alternative combines flow detention, bypass, and riparian restoration elements to reduce design flows such that existing and restored channel reaches can convey flows safely downstream. Conceptual alternative X is composed of the following Conceptual Project Elements: • CPE 2 -Flow Detention South Branch Dam: Permanente Creek Flood Protection Project Page 82 Planning Study Report July 2008 A new concrete dam would be built in the far upstream reach of South Branch Permanente Creek in the Hanson PermanE~nte Quarry. The dam would be approximately 100 feet high and 500 feet v~ride at the top. The dam outlet would be open at all times such that the dam would only irnpound water during rainfall events that cause flows in excess of 50 cubic feet per second (cfs). CPE 7 -Hale Bypass: An underground bypass consisting of an 8••foot by 8-foot concrete box culvert would be constructed a length of approximately 3,000 feet. The bypass would be constructed under local residential roadways from a fevv hundred feet downstream of Foothill Expressway to the beginning of the concrete Hale Creek section at Rosita Avenue. For this alternative, Hale Bypass would be extE~nded for an additional 4400 feet along Cuesta Drive to Cuesta Park Annex. CPE 8 -Permanente Bypass: This bypass would consist of two different ;sizes. The upstream portion would be a 54-inch pipe culvert bypass channel from Eastwood Drive to St. Francis School. The downstream portion would consist of an 8=foot by 6-foor box culvert from the school to Cuesta Park Annex. The channel along Reach P8 from the Diversion to Portland Ave would also have to be improved by replacing the concrete channel. • CPE 9 - Floodwalls: Downstream of Highway 101 along Reach P2 would be modified by the addition of 1-foot to 3-foot high concrete floodwalls to the levee channels. • CPE 12 -Riparian Restoration: The existing concrete channel in reaches F'3 and P5 would be replaced with an earth channel with riparian vegetation. The channel invert may require rock lining, based on velocity parameters. • CPE 19 -New Diversion Structure: The existing diversion structure and 54-inch pipeline would be abandoned and replaced by a new structure. The inlet to the new structure would be along Miramonte Avenue just upstream of the current eastward bend. Anew 8-foot by 8-foot box culvert would convey the flows under Miramonte Avenue to connect with the creek at Eastwood Place. • CPE 20 -Flood Detention Cuesta Park i~nnex: A flood detention facility would be created ~~n the Cuesta Park Annex property of the City of Mountain View. The average depth of the 12-acre facility would be 15 feet, producing approximately 130 acre-feet of storage volume. 10-year or higher flow events would be routed to the facility. A 36-inch outlet pipe would drain the stored volume back to the creek, once the peak flows would pass. Technical Feasibility All project elements are technically feasible. Costs Capital cost for the entire alternative would be: $60,000,000. Permanente Creek Flood Protection Project Page 83 Planning Study Report July 2008 Capital costs for the CSC portion would be $30,000,000. CONCEPTUAL ALTERNATIVE Y Alternative Description This alternative combines flow detention, bypass, and riparian restoration elements to reduce design flows such that existing and restored channel reaches can convey flows safely downstream. Conceptual alternative Y is composed of the following Conceptual Project Elements: CPE 3 -Flow Detention Rancho San Antonio: An off-stream detention facility would be created on a parcel owned by the County of Santa Clara Parks Department next to the Rancho San Antonio County Park. The average depth of the approximately 5 acre detention facility would be 15 feet, producing approximately 75 acre-feet of storage volume. The site would be contoured to resemble natural relief. CPE 7 -Hale Bypass: An underground bypass consisting of an 8-foot by 8-foot concrete box culvert would be constructed a length of approximately 3,000 feet. The bypass would be constructed under local residential roadways from a few hundred feet downstream of Foothill Expressway to the beginning of the concrete Hale Creek section at Rosita Avenue. For this alternative, Hale Bypass would be extended for an additional 4,400 feet along Cuesta Drive to Cuesta Park Annex. • CPE 8 -Permanente Bypass: An underground bypass consisting of a 6-foot diameter pipe culvert would be constructed a length of approximately 3400 feet from the Blach School detention area to the Cuesta Park Annex under local streets. • CPE 9 - Floodwalls: Downstream of Highway 101 along Reach P2 would be modified by the addition of 1-foot to 3-foot high concrete floodwalls to the levee channels. • CPE 12 -Riparian Restoration: The existing concrete channel in reaches P3 and P5 would be replaced with an earth channel with riparian vegetation. The channel invert may require rock lining, based on velocity parameters. • CPE 19 -New Diversion Structure: The existing diversion structure and 54-inch pipeline would be abandoned and replaced by a new structure. The inlet to the new structure would be along Miramonte Avenue just upstream of the current eastward bend. Anew 8-foot by 8-foot box culvert would convey the flows under Miramonte Avenue to connect with the creek at Eastwood Place. • CPE 20 -Flood Detention Cuesta Park Annex: A flood detention facility would be created on the Cuesta Park Annex property of the City of Mountain View. The average depth of the 12-acre facility would be 15 feet, producing approximately 130 acre-feet of storage volume. 10-year or higher flow events would be Permanente Creek Flood Protection Project Page 84 Planning Study Report July 2008 routed to the facility. A 36-inch outlet pipe would drain the stored volume back to the creek, once the peak flows would pass. CPE 21 -Flood Detention Blach School: A flood detention facility would be created in Blach Jr. High School's athletic fields. The average depth of the 5-acre facility would k-e 15 feet, producing approximately 65 acre-feet of storage volume. 10-year or higher flow events would be routed to the facility from Permanente Diversion, which would be modified for this purpose at this location. Technical Feasibility This project element is technically feasible with current construction techniques. Costs Capital costs would be $57,000,000. Capital costs for the CSC portion would be $48,000,000. CONCEPTUAL ALTERNATIVE Z Alternative Description This alternative combines flow detention, bypass, and riparian restoration elements to reduce design flows such that existing and restored channel reaches can convey flows safely downstream. Conceptual alternative Z is composE~d of the following Conceptual Project Elements: CPE 3 -Flow Detention Rancho San Anfonio: An off-stream detention facility would be created on a parcel owned by the County of Santa Clara Parks Department next to the Rancho San Antonio County Park. The average depth of the approximately 5 acre detention facility would be 15 feet, producing approximately 75 acre-feet of storage volume. The site would be contoured to resemble natural relief. CPE 5 -Flow Detention McKelvey Park: An off-stream detention facility would be created on the current baseball fields at McKelvey Park in the city of Mountain Vierri. The average depth of the approximately 5 acre detention facility would be approximately 13 feet, producing approximately 60 acre-feet of storage volume. CPE 7 -Hale Bypass: An underground bypass consisting of an 8••foot by 8-foot concrete box culvert would be constructed a length of approximately 3,000 feet. The bypass would be constructed under local residential roadways from a fevv hundred feet downstream of Foothill Expressway to the beginning of the concrete Hale Creek section at Rosita Avenue. CPE 8 -Permanente Bypass: An underground bypass consisting of a 6-f~~ot diameter pipe culvert would be constructed a length of approximately 340() feet from the Blach School detention area to the Cuesta Park Annex under local streets.. Permanente Creek Flood Protection Project Page 85 Planning Study Report July 2008 • CPE 9 - Floodwalls: Downstream of Highway 101 along Reach P2 would be modified by the addition of 1-foot to 3-foot high concrete floodwalls to the levee channels. • CPE 12 -Riparian Restoration: The existing concrete channel in reaches P3 and P5 would be replaced with an earth channel with riparian vegetation. The channel invert may require rock lining, based on velocity parameters. • CPE 17 -Hale Improvement: The existing concrete channel in reach H1 would be improved by lowering the bottom of the channel and removing drop structures within the existing District right-of-way. This would improve the capacity of the reach to the full design flow. • CPE 19 -New Diversion Structure: The existing diversion structure and 54-inch pipeline would be abandoned and replaced by a new structure. The inlet to the new structure would be along Miramonte Avenue just upstream of the current eastward bend. Anew 8-foot by 8-foot box culvert would convey the flows under Miramonte Avenue to connect with the creek at Eastwood Place. • CPE 20 -Flood Detention Cuesta Park Annex: A flood detention facility would be created on the Cuesta Park Annex property of the City of Mountain View. The average depth of the 7-acre facility would be 10 feet, producing approximately 65 acre-feet of storage volume. 10-year or higher flow events would be routed to the facility. A 36-inch outlet pipe would drain the stored volume back to the creek, once the peak flows would pass. CPE 21-Flood Detention Blach School: A flood detention facility would be created in Blach Jr. High School's athletic fields. The average depth of the 5-acre facility would be 15 feet, producing approximately 65 acre-feet of storage volume. 10-year or higher flow events would be routed to the facility from Permanente Diversion, which would be modified for this purpose at this location. Technical Feasibility This project element is technically feasible with current construction techniques. Costs Capital costs would be $50,000,000. Capital costs for the CSC portion would be $34,000,000 4.5 Conceptual Alternatives Screening Methodology Screening during the conceptual alternatives phase of the project is defined as Level 1 screening. Level 1 screening focuses on the project objectives, costs, technical feasibility, and right-of-way availability. The Level 1 screening criteria are described below. Permanente Creek Flood Protection Project Page 86 Planning Study Report July 2008 Project Objectives: Conceptual alternatives muss: satisfy the project objectives in order to be carried forward to the feasible analysis stage. Thus, each alternative was analyzed as to whether it met the project's objectives. Project Cost: The project's budget for detailed design and construction is approximately $35 million. To allow for evaluation of a full range of alternatives for the District Board, the affordability cut off line for conceptual alternatives was set at double the project budget ($70 million). Alternatives that provide the flood p~~otection and other project objectives required for under $70 million were considered for feasibility. Note that all costs are in 2005 $. Technical Feasibility: This parameter indicates if all project elements can be actually built using widely available construction materials and Know-how. Alternatives that were determined to be technically feasible could be allowed to continue to the feasible alternatives phase. Right-of-Way Availability: This parameter refers to whether or not the non-District owned right-of-way required by the alternative is likely to Ise available for the intended District use. Conceptual alternatives that would likely have available rights-of-way could be carried forward into the feasibility analysis stage. Of the 26 conceptual alternatives analyzed, the 11 alternatives that satisfied all of the Level 1 screening criteria (see Table 4.1) plus the "no project" alternative were carried forward into the feasible alternatives stage of the project. Alternatives that failed to satisfy any one of the above four criteria were eliminated from further consider~ition. 4.6 Feasible Alternatives Description The 11 feasible alternatives and the no project altE~rnative were analyzed in more detail. Some of the elements were changed to reflect better design or to meet actual site conditions. Some of the bypass sizes were changed and floodwall lengths and heights were refined. Two of the CPEs were more radically altered: CPE 12: Riparian Restoration -After more detailed analysis, it became clear that the extent of possible riparian restoration had to be reduced. The limited right-of-way available along most of the concrete channels did not allow adequate spa~;e for both a restored channel and maintenance access. Since maintenance access would be crucial to the long-term success of the restoration, it was decided that the maximum Extent of this project element would be from Highway 101 to Middlefield Road, approximately 2,300 feet. CPE 17: Hale Improvements -After discussions with structural experts, it was determined that this CPE was not technically as feasible as full removal and reconstruction of the trapezoidal concrete channels along Hale Creek would be. TFierefore, the alternatives containing CPE 17 were edited to include CPE 10 (channel widening) instead. Once the required changes were made, the "no project' alternative and the other 11 alternatives which passed the level 1 screening were analyzed in detail. These alternatives are described below and are summarized in Table 4.2 -Summary of Feasible Alternatives. Maps for all the feasible alternatives are provided in Appendix B. ALTERNATIVE A Description Permanente Creek Flood Protection Project Page 87 Planning Study Report July 2008 This is the "no project" alternative. This alternative proposes to continue the current level of sediment, bank, and vegetation maintenance effort. This alternative would also include continuous monitoring of the concrete channel reaches in order to determine if reaches are nearing preset failure thresholds (see September 2000 Biggs Cardosa Structural Integrity Study) and replacing channels in-kind once they do reach that threshold. It is anticipated that half of the current concrete channel length in reaches P3, P5, and H1 will fail over the project life (next 50 years). Construction Schedule There would be no new capital work involved with this alternative. Operation and Maintenance (O&M) Existing O&M activities include sediment removal in the Permanente Diversion and in Permanente Creek downstream of Highway 101. They also include typical maintenance activities such as trash and debris removal, graffiti removal, vegetation (overgrowth) removal, and erosion repair in natural sections. Land Ownership/Access No new right-of-way acquisition would be required. Costs Capital cost for this alternative would be: $0 50 year maintenance cost (current maintenance activities) would be $29 million. See Appendix E for costs details. Preliminary Environmental Review Preliminary environmental review has revealed potential for impacts to biological resources and water quality. Detailed results will not be available until an evaluation of potential impacts and mitigation measures has been carried out through the California Environmental Quality Act (CEQA) process. ALTERNATIVE D Description This alternative combines channel expansion, floodwall and bypass elements to increase the capacity of all channel reaches to the design flows, while avoiding major impacts to existing creek resources. The project elements shown in italic font below are those that would not be constructed in the current CSC phase. See Appendix B for a map showing all project elements and flood benefit areas (note that map element shown in blue are those that would be built in the current CSC phase, while those displayed in red would be built in potential future phases). Alternative D is composed of the following project elements: Hale Byaass: Permanente Creek Flood Protection Project Page 88 Planning Study Report July 2008 An underground bypass consisting of an 8•~foot by 6-foot concrete box culvert 3,700 feet long would be constructed. The bypass would be constructed under local residential roadways from iusf downstream of Foothill Expressway to the beginning of the concrete Hale Creek section at Rosita Avenue. Permanente Bypass: An underground bypass consisting of an 8•~foot by 6.5-foot concrete box culvert for 4000 feet plus a 10-foot by 7-foot concrete box culvert for 5800 feet would be constructed from Reach P8 to Reach P5. The proposed bypass culvert would begin upstream of the Permanente Diversion, follow Miramonte Avenue to Trophy Drive and reconnect to the Permanente Creek channel lust upstream ~~f E/ Camino Real. • Floodwalls: Permanente Creek downstream of Highway 101 along Reach P2 and the lower portion of Reach P3 would be modified by the addition of 5-foot to 8-foot high floodwalls to the top of the existing levees. • Channel Widening: All existing concrete U-frame channels (Reaches P3, P5, and H1) would be removed and rebuilt wider. In addition, most bridge:. and culverts in the project area would be similarly enlarged to contain the one-percent design flow. • EI Camino Bypass: An underground bypass consisting of a 10-foot by 8-foot concrete box culvert approximately 2500 feet long would be constructed around a portion of the existing EI Camino Real culvert. The new culvert would start at EI Camino Real and go north and west along local streets and reconnect with the existing culvert at Latham Street. • EI Camino Culvert: The portion of underground box culvert between Latham and Villa Street would be enlarged by the addition of a new 10-foot by 10-foot box culvert. • EI Camino Collection Channel: 1400 feet of 5-foot diameter and 1600 feet of 9-foot diameter reinforced concrete pipe (RCP) culvert would be installed under one lane of northbound EI Camino Real. Grated inlets would be installed along EI Camino Fieal to allow flood waters from upstream flooding to be captured by the new culvert. • New Diversion Structure: The existing diversion structure and 54-ina~ipeline would be abandoned. There would be a new outlet to the natural channel at E<~stwood Drive provided through a small culvert from the Permanente Bypass described above. Construction Schedule Constructing floodwalls would likely take 1 to-2 ye~~rs. Construction of the bypasses and flood collection channel would be completed in 2 to 4 years, depending on difficulties with existing utilities located beneath the local roadways. Channel widening would take 3-4 years, in stages. Operation and Maintenance Permanente Creek Flood Protection Project Page 89 Planning Study Report July 2008 Existing O&M activities are expected to continue on the rebuilt concrete channels; no additional maintenance activities would be required. Typical maintenance activities include trash and debris removal, graffiti removal, vegetation (overgrowth) removal, erosion repair in natural sections, and sediment removal in the Permanente Diversion and Reach P2. Operation and maintenance of the bypasses would be minimal. The bypass culverts would be designed to have adequate slope for sediment control. Operation and maintenance for the new Latham to Villa Street culvert would be similar to existing culvert. The culvert would be designed to have adequate slope for sediment passage. Costs Capital cost for the entire alternative would be: $118 million (2008 dollars). Capital cost for the portion required under CSC would be: $59 million. 50 year maintenance cost (including current maintenance activities) would be $27 million. See Appendix E for costs details for alt alternatives. Preliminary Environmental Review Preliminary environmental review has revealed potential for impacts to hydrology and water quality, biological resources, cultural resources, aesthetics, traffic/utilities, noise, air quality, health and safety, and recreation. Detailed results will not be available until an evaluation of potential impacts and mitigation measures has been carried out through the California Environmental Quality Act (CEQA) process. ALTERNATIVE E Description This alternative is very similar to alternative D. It combines channel expansion and bypass elements to increase the capacity of all channel reaches to the design flows, while avoiding major impacts to existing creek resources. The project elements shown in italic font are those that would not be constructed in the current CSC phase. See Appendix B for a map showing all project elements and flood benefit areas. Alternative E is composed of the following project elements: • Hale Bypass: See Alternative D. • Permanente Bypass: See Alternative D. • Floodwalls: See Alternative D. • Channel Widening: See Alternative D. • EI Camino Bypass: An underground bypass consisting of a 10-foot by 8-foot concrete box culvert approximately 4800 feet long would be constructed around the existing EI Camino to Permanente Creek Flood Protection Project Page 90 Planning Study Report July 2008 Villa Street culverts. The new culvert would start just north of EI Camino Real and go north and west along local streets and rec~~nnect with the existing channel at Villa Street. EI Camino Collection Channel: See alternative D. New Diversion Structure: See Alternative D. Construction Schedule See Alternative D. Operation and Maintenance See Alternative D. Costs Capital cost for the entire alternative would be: $121 million (2008 dollars). Capital cost for the portion required under CSC would be: $62 million. 50-year maintenance costs (including current maintenance) would be $27 million. See Appendix E for cost estimate details. Preliminary Environmental Review See Alternative D. ALTERNATIVE G Alternative Description This alternative combines flow detention, bypass, ,and riparian restoration elements to reduce design flows such that existing and restored channel reaches could convey flows safely downstream. The ,vroiect elements shown in italic font are those that would not be constructed in the current CSC phase. See Appendix B for a map showing all project elements and flood benefit areas. Alternative G is composed of the following project elements: Flow Detention South Branch Dam: A new concrete dam would be built in the fs~r upstream reach of South Branch Permanente Creek in the Hanson PermanE~nte Quarry. The dam would be approximately 100 feet high and 500 feet wide at the top, with a storage volume of more than 300 acre-feet and impoundment surfa~~e area of approximately 11 acres. The dam outlet would be open at all times such that 'the dam would begin to impound water during rainfall events that cause flows in excess o1~ 50 cubic feet per second (cfs), which is a yearly flow event. Flow Detention Rancho San Antonio: An off-stream detention facility would be crE~ated on a parcel owned by the County of Santa Clara in Rancho San Antonio County Park. The average depth of the approximately 8-acre detention facility would be 15 feet, producing approximately Permanente Creek Flood Protection Project Page 91 Planning Study Report July 2008 100 acre-feet of storage volume. The site would be contoured to resemble natural relief. Only 10-year or higher flow events would be diverted into the facility. A 24-inch outlet pipe would drain the pond back into the creek, once peak flows passed. The inlet would be by way of a rebuilt bridge a few hundred feet upstream of the pond. The current low flow crossing would be replaced by an at-grade bridge, with fill (from the pond excavation) placed on the West bank to confine high flows. The new culvert would be sized for the design flow split, forcing excess flows to spill into a side channel located on the East side of the creek. Flow Detention McKelvey Park: An off-stream detention facility would be created on the current baseball fields at McKelvey Park in the city of Mountain View. The average depth of the approximately 5- acre detention facility would be approximately 13.5 feet, producing approximately 60 acre-feet of storage volume. Only 10-year or higher flow events would be diverted into the facility. A 24-inch outlet pipe would drain the flood flows back to the creek once the peak flows passed. • Hale Bvpass: See Alternative D. • Floodwalls: Permanente Creek from down-stream of Amphitheater Parkway to Highway 101 would be modified by the addition of floodwalls averaging 2 feet high to the top of the existing levees. • Channel Widening: Existing concrete channels along reaches P5 and H1 would be removed and rebuilt wider. In addition, several bridges and culverts in the project area would be similarly modified (widened/enlarged) to contain the one-percent design flow. • Riparian Restoration: The existing concrete channel in reach P3 from Hiahwav 101 to Middlefield Road would be replaced with a combined concrete and earth channel with riparian vegetation. The channel would be hardened on one side (concrete C~1 1:2 side slopes) with a natural bottom bankfull channel with (partial) f/oodplain and vegetated earth bank C~? 1.5:1 side slopes. New Diversion Structure: The existing diversion structure would be abandoned and replaced by a new pipe connection to the existing 54-inch pipe. The inlet to the new structure would be along Miramonte Avenue just upstream of the current eastward bend (looking downstream) of the creek. Construction Schedule Construction of the dam would likely take two years. The Rancho San Antonio and McKelvey Park detention sites would likely take one year each. Construction and installation of the bypass would be completed in 2 to 4 years, depending on difficulties with existing utilities located beneath the local roadways. Construction of the riparian earth channel would occur Permanente Creek Flood Protection Project Page 92 Planning Study Report July 2008 over stages in 4 to 8 years. The diversion structure improvement could be built in 1/2 year. Channel widening and floodwalls would take 1-2 years, in stages. Operation and Maintenance The new dam and its outlet would have to be maintained in good and safe conditions. The inlet area and the outlet would have to be cleared of sediment as needed. The Rancho San Antonio detention pond would only need regular maintenance for its inlet/outlet works. The pond area itself would need minimal maintenance, as vegetation and sediment can be allowed to accumulate over time. The McKelvey Park detention area would have to be maintained for its intended use as a baseball facility. Thus, the area would have to be quickly cleared of silt and other flood debris after any flooding event, and the playing surfaces (dirt areas, chalk lines, etc.) would be restored. A maintenance agreement could be set up with a private company, which would relieve District crews from having to add this non-typical work to their flood fighting duties. Existing sediment O&M activities in the Permanente Diversion would be reduced somewhat due to the reduced flow peaks from the dam upstream, Typical maintenance activities include trash and debris removal, graffiti removal, vegetation (o~rergrowth) removal, erosion repair in natural sections, and sediment removal in the Permanente Diversion and Reach P2. Operation and maintenance of the bypass would be limited to inlE~t/outlet vegetation and sediment control. The bypass culvert would be designed to have adequate slope for sediment control. Operation and maintenance of the riparian channel would be to encourage appropriate vegetation growth and to repair bank failures. Activities would be limited by access issues along most reaches. Costs Capital cost for the entire alternative would be: $5r) million (2008 dollars). Capital cost for the CSC portion of the work would be $32 million. 50-year cost for maintenance (including current work) would be $30 million. See Appendix E for cost estimate details. Preliminary Environmental Review See Alternative D. ALTERNATIVE S Alternative Description This alternative is very similar to alternative G. It combines flow detention, bypass, and riparian restoration elements to reduce design flows such i:hat existing and restored channel reaches could convey flows safely downstream. The proiec:t elements shown in italic font are those that would not be constructed in the current CSC phase. See Appendix B for a map showing all project elements and flood benefit areas. Alternative S is composed of the following project elements: Flow Detention Rancho San Antonio: See Alternative G. Permanente Creek Flood Protection Project Page 93 Planning Study Report July 2008 • Flow Detention McKelvey Park: See Alternative G. • Hale Bypass: See Alternative D. • Permanente Bypass: An 8' by 5.5' bypass channel would be constructed for a /enpth of 2200' from the St. Francis School bridge to the Cuesta Park Annex under Miramonte and Cuesta Avenues. • Floodwalls: See Alternative G. • Channel Widening: See Alternative G. • Riparian Restoration: See Alternative G. • New Diversion Structure: The existin4 diversion structure and pipeline would be abandoned. The inlet to the new structure would be a/onp Miramonte Avenue iust upstream of the current eastward bend of the creek (looking downstream). Anew 8-foot diameter RCP culvert would convey the flows under Miramonte Avenue to connect with the creek at Eastwood Drive. • Flow Detention Cuesta Park Annex: An off-stream detention facility would be created on the Cuesta Park Annex property of the City of Mountain View. There would be an open part of the storage on the north side of Cuesta Park Annex, which would be composed of approximately 5 acres excavated to 20 feet deep and landscaped with park vegetation and features. There would also be an underground portion, located under the parking lot area in the developed part of Cuesta Park. This area would be excavated 30 feet deep, with the parking lot replaced on top of the detention area. The total storage volume would be approximately 130 acre-feet. Only 10-year or higher flow events would be diverted into the facility. A 36-inch outlet pipe would drain the flood flows back to Permanente Creek, once the flood peak passed. The outlet pipe would go West to Miramonte Ave, North to Trophy Drive and West to Permanente Creek. Construction Schedule See Alternative G. Cuesta Park Annex detention sites would likely take one year to build. Operation and Maintenance See Alternative G. The Cuesta Park Annex detention pond would have to be maintained for its intended use as a public facility. Thus, the area would have to be cleared of silt and other flood debris after any flooding event and the surfaces restored. Costs Permanente Creek Flood Protection Project Page 94 Planning Study Report July 2008 Capital cost for the entire alternative would be: $6'7 million (2008 dollars). Capital cost for the CSC portion of the work would be $41 million. 50-year cost for maintenance (including current work) would be $21 million. See Appendix E for cost estimate details. Preliminary Environmental Review See Alternative D. ALTERNATIVE T Alternative Description This alternative is very similar to Alternative G. It ~;ombines flow detention, bypass, and riparian restoration elements to reduce design flows such 1:hat existing and restored channel reaches could convey flows safely downstream. The proiect elements shown in italic font are those that would not be constructed in the current CSC phase. See Appendix B for a map showing all project elements and flood benefit areas. Alternative T is composed of the following project elements: Flow Detention McKelvey Park: See Alternative G. Hale Bypass: See Alternative D. Permanente Bypass: This bypass would consist of two different ,sizes. The upstream half would consist of an 8' by 7' bypass channel from Eastwood Dr. to St Francis School. The downstream half would consist of a 12' by 7' bypass channE~l from St. Francis School to Cuesta Park Annex. This ,vroiect element would also include improving the channel portion from stream of Portland Ave to the Permanente Diversion by rebuilding the concrete channel. • Floodwalls: See Alternative G. • Channel Widening: See Alternative G. • Riparian Restoration: See Alternative G. • New Diversion Structure: See Alternative S. • Flow Detention Cuesta Park Annex An off-stream detention facility would be created on the Cuesta Park Annex property of the City of Mountain View. The average dE~pth of the approximately 12-acre detention facility would be approximately 20 feet, producing approximately 240 acre-feet of storage Permanente Creek Flood Protection Project Page 95 Planning Study Report July 2008 volume. Only 10-year or higher flow events would be diverted into the facility. A 48-inch outlet pipe would drain the flood flows back to the creek, once the flood peak passed. The outlet pipe would go West to Miramonte Ave, North to Trophy Drive and West to Permanente Creek. Construction Schedule See Alternative S. Operation and Maintenance See Alternative S. No impacts at Rancho San Antonio. Costs Capital cost for the entire alternative would be: $68 million (2008 dollars). Capital cost for the CSC portion of the work would be $29 million. 50-year cost for maintenance (including current work) would be $22 million. See Appendix E for cost estimate details. Preliminary Environmental Review See Alternative D. ALTERNATIVE U Alternative Description This alternative combines flow detention, bypass, and channel enlargement elements to partially reduce design flows such that the expanded channel portions could convey flows safely downstream. The proiect elements shown in italic font are those that would not be constructed in the current CSC phase. See Appendix B for a map showing all project elements and flood benefit areas. Alternative U is composed of the following project elements: • Flow Detention South Branch Dam: See Alternative G. • Flow Detention Rancho San Antonio: See Alternative G. • Hale Byaass: See Alternative D. • Floodwalls: Permanente Creek from down-stream of Amphitheater Parkway to Highway 101 along Reach P2 would be modified by the addition of floodwalls averaging 3 feet high to the top of the existing levees. • Channel Widening: Permanente Creek Flood Protection Project Page 96 Planning Study Report July 2008 Existing concrete channels along reaches P3, P5 and H1 would be removed and rebuilt wider. In addition, several bridges and culverts in the project area would be similarly modified (widened/enlarged) to contain they one-percent design flow. EI Camino Bypass: An underground bypass consisting of a 6-foot diameter reinforced concrete pipe (RCP) approximately 4800 feet long would be constructed around the existing EI Camino to Villa Street culverts. The new culvert will start just north of EI Camino Real and go north and west along local streets and reconnect with the existing channel at Villa Street. New Diversion Structure: See Alternative G. Construction Schedule Construction of the dam would likely take two years. The Rancho San Antonio detention site would likely take one year. Construction and installation of the bypasses would each be completed in 2 to 4 years, depending on difficultie:> with existing utilities located beneath the local roadways. The diversion structure improvement could be built in 1/2 year. Operation and Maintenance See Alternative G. Costs Capital cost for the entire alternative would be: $6ff million (2008 dollars). Capital cost for the CSC portion of the work would be $51 million. 50-year cost for maintenance (including current wc-rk) would be $29 million. See Appendix E for cost estimate details. Preliminary Environmental Review See Alternative D. ALTERNATIVE V Alternative Description This alternative combines flow detention, bypass, rind riparian restoration elements to reduce design flows such that existing and restored channel reaches could convey flows safely downstream. The Qroiect elements shown in italic 1`ont are those that would not be constructed in the current CSC phase. See Appendix B for a map showing all project elements and flood benefit areas. Alternative V is composed of the following project elements: Flow Detention South Branch Dam: See Alternative G. Flow Detention Rancho San Antonio: See Alternative G. Permanente Creek Flood Protection Project Page 97 Planning Study Report July 2008 Flow Detention Cuesta Park Annex An off-stream detention facility would be created on the Cuesta Park Annex property of the City of Mountain View. The maximum depth of the approximately 5-acre detention facility would be 12 feet, producing approximately 60 acre-feet of storage volume. Only 10-year or higher flow events would be diverted into the facility. A 24-inch outlet pipe would drain the flood flows back to the creek, once the flood peak passed. The outlet pipe would go West to Miramonte Avenue North to Trophy Drive and West to Permanente Creek. • Hale Bvpass: See Alternative D. • Extended Hale Bypass: A 7' by 6' box culvert approximately 4400 feet long would be constructed under local streets from the end of the Hale Bypass channel to the Cuesta Park Annex detention site. The bypass route would follow Springer Road and Cuesta Avenue. • Floodwalls: See Alternative G. • Channel Widening: The existing concrete channel along reach P5 would be removed and rebuilt wider. In addition, two bridges in Reach H1 would be similarly modified (widened/enlarged) to contain the one-percent design flow. • Riparian Restoration: See Alternative G. • New Diversion Structure: See Alternative G. Construction Schedule See Alternative S. The extended bypass would require 1 to 2 years of construction. Operation and Maintenance See Alternative S. Costs Capital cost for the entire alternative would be: $47 million (2008 dollars). Capital cost for the CSC portion of the work would be $37 million. 50-year cost for maintenance (including current work) would be $29 million. See Appendix E for cost estimate details. Preliminary Environmental Review See Alternative D. Permanente Creek Flood Protection Project Page 98 Planning Study Report July 2008 ALTERNATIVE W Alternative Description This alternative combines flow detention, bypass, and riparian restoration elements to reduce design flows such that existing and restored channel reaches could convey flows safely downstream. The project elements shown in italic font are those that would not be constructed in the current CSC phase. See Appendix B for a reap showing all project elements and flood benefit areas. Alternative W is composed of the following project elements: • Flow Detention South Branch Dam: See Alternative G. • Flow Detention McKelvey Park: See Alternative G. • Hale Bypass: See Alternative D. • Permanente Bvvass: This bvpass would consist of two different sizes. The upstream half would consist of a 54-inch RCP bvpass channel from Eastwood Dr. to St. Francis School. The downstream half would consist of an 8' by 6' bvpass ch,~nnel from St. Francis School to Cuesta Park Annex. • Floodwalls: See Alternative G. • Channel Widening: See Alternative G. • Riparian Restoration: See Alternative G. • New Diversion Structure: See Alternative S. • Flow Detention Cuesta Park Annex An off-stream detention facility would be created on the Cuesta Park Annex property of the City of Mountain View. The average dc~pth of the approximately 5-acre detention facility would be 13 feet, producing approximately 70 acre-feet of storage volume. Only 10-year or higher flow events would be diverted into the facility. A 24-inch outlet pipe would drain the flood flows back to the creE~k, once the flood peak passed. The outlet pipe would go West to Miramonte Ave, North to Trophy Drive and West to Permanente Creek. Construction Schedule See Alternative S. Permanente Creek Flood Protection Project Page 99 Planning Study Report July 2008 Operation and Maintenance See Alternative S. Costs Capital cost for the entire alternative would be: $56 million (2008 dollars). Capital cost for the CSC portion of the work would be $29 million. 50-year cost for maintenance (including current work) would be $31 million. See Appendix E for cost estimate details. Preliminary Environmental Review See Alternative D. ALTERNATIVE X Alternative Description This alternative combines flow detention, bypass, and riparian restoration elements to reduce design flows such that existing and restored channel reaches could convey flows safely downstream. The project elements shown in italic font are those that would not be constructed in the current CSC phase. See Figure Appendix B for a map showing all project elements and flood benefit areas. Alternative X is composed of the following project elements: • Flow Detention South Branch Dam: See Alternative G. • Hale Bypass: See Alternative D. • Extended Hale Bypass: See Alternative V. • Permanente Bypass: See Alternative W. • Floodwalls: See Alternative G. • Channel Widening: See Alternative V. • Riparian Restoration: See Alternative G. • New Diversion Structure: See Alternative S. • Flow Detention Cuesta Park Annex Permanente Creek Flood Protection Project Page 100 Planning Study Report July 2008 See Alternative S. Construction Schedule See Alternative V. Operation and Maintenance See Alternative V. Costs Capital cost for the entire alternative would be: $63 million. Capital cost for the CSC portion of the work would be $44 million. 50-year cost for maintenance (including current w~~rk) would be $29 million. See Appendix E for cost estimate details. Preliminary Environmental Review See Alternative D. ALTERNATIVE Y Alternative Description This alternative combines flow detention, bypass, and riparian restoration elements to reduce design flows such that existing and restored channel reaches could convey flows safely downstream. The project elements shown in italic font are those that would not be constructed in the current CSC phase. See Appendix B for a rnap showing all project elements and flood benefit areas. Alternative Y is composed of the following project elements: Flow Detention Rancho San Antonio: See Alternative G. Flow Detention Blach Intermediate School: An underground detention pond would be created on 5 acres of Blach SchooPs athletic fields. The area would be excavated to a depth of 30 feet with 1:1 side slopes lined with rock. The athletic fields would be rebuilt on top of a concrete deck which would be constructed over the pond area on piers. l-he flow inlet would be through an overflow weir from the adjacent Permanente Diversion Channel and the outlet would be directly to the Diversion Channel using built in place mumps. Hale Bypass: See Alternative D. Extended Hale Bypass: See Alternative V. Permanente Bypass: Permanente Creek Flood Protection Project Page 101 Planning Study Report July 2008 An 8-foot diameter concrete pipe culvert would connect the Blach School flood detention site with Cuesta Park Annex flood detention site. The pipe would run under local streets (Covington, Thatcher, and Hospital) for 3400 feet. • Floodwalls: See Alternative G. Additional floodwalls would be needed just upstream of Blach School. • Channel Widening: See Alternative V. • Riparian Restoration: See Alternative G. • New Diversion Structure: See Alternative G. • Flow Detention Cuesta Park Annex See Alternative S. Construction Schedule See Alternative S. Operation and Maintenance See Alternative S. Instead of McKelvey Park, it is Blach School that would need to be maintained and restored to playable conditions post any flood events. Costs Capital cost for the entire alternative would be: $66 million (2008 dollars). Capital cost for the CSC portion of the work would be $55 million. 50-year cost for maintenance (including current work) would be $21 million. See Appendix E for cost estimate details. Preliminary Environmental Review See Alternative D. ALTERNATIVE Z Alternative Description This alternative combines flow detention, bypass, and riparian restoration elements to reduce design flows such that existing and restored channel reaches could convey flows safely downstream. The oroiect elements shown in italic font are those that would not be constructed in the current CSC phase. See Appendix B for a map showing alt project elements and flood benefit areas. Alternative Z is composed of the following project elements: Flow Detention Rancho San Antonio: Permanente Creek Flood Protection Project Page 102 Planning Study Report July 2008 See Alternative G. • Flow Detention Blach Intermediate School: See Alternative Y. • Flow Detention McKelvey Park: See Alternative G. • Hale Bypass: See Alternative D. • Permanente Bypass: See Alternative Y. • Floodwalls: See Alternative Y. • Channel Widening: See Alternative G. • Riparian Restoration: See Alternative G. • New Diversion Structure: See Alternative G. Construction Schedule See Alternative S. Blach School detention construction would likely take approximately one year. Operation and Maintenance See Alternative Y. McKelvey Park would need to tie maintained post-flood as well. Costs Capital cost for the entire alternative would be: $58 million (2008 dollars). Capital cost for the CSC portion of the work would be $40 million. 50-year cost for maintenance (including current work) would be $22 million. See Appendix E for cost estimate details. Preliminary Environmental Review See Alternative D. 4.7 Alternative Ranking Methodology 4.7.1 Natural Flood Protection The District Board of Directors has adopted an Encis Policy that requires "natural flood protection" to be the method the District uses to pr~~vide flood protection to the citizens of the County. Ends Policy 2.2.1 states: "There is natural flood protection that balances environmental Permanente Creek Flood Protection Project Page 103 Planning Study Report July 2008 quality, community benefit and protection from creek flooding in ~ cost effective manner. In providing flood protection, balance the following multiple objectives: 1. Homes, schools, businesses, and transportation networks are protected from flooding and erosion. 2. Ecological functions and processes are supported. 3. Physical stream functions and processes are integrated. 4. Maintenance requirements are minimized. 5. Projects are integrated within the watershed as a whole. 6. The quality and availability of water is protected. 7. Cooperation with local agencies achieves mutually beneficial goals. 8. Community benefits beyond flood protection. 9. Life-cycle costs are minimized." To comply with this ends policy, a Natural Flood Protection (NFP) procedure was developed. This report used the NFP procedure (see August 2005 "Guidance on Alternative Evaluation and Selection for natural Flood Protection Projects") to rate and compare the feasible alternatives. 4.7.2 Summary of the NFP Procedure As required by the ends policy, the procedure balances the nine NFP objectives. Various criteria (as few as one to as many as seven) were developed to help rate each objective. These criteria were: Objective 1: provide protection from flood damage Criterion 1: safety -protection of public safety if conditions exceed design assumptions Criterion 2: economic protection -protection from damage due to floodwaters, erosion or sediment Criterion 3: durability -future effort required to maintain design level of protection Criterion 4: resiliency -adaptability to future changes Criterion 5: local drainage -support of local storm drain systems Criterion 6: time to implementation -how quickly flood protection elements could become effective Objective 2: support ecological functions and processes Criterion 1: local habitat goals -ability to meet habitat goals as defined from examining the watershed as a whole Criterion 2: habitat provided -quality of habitat provided by alternative Criterion 3: sustainability of habitat -intensity of future action required to maintain design habitat quality Criterion 4: connectivity of habitat -integration of habitat elements into surrounding landscape Objective 3: physical stream functions and processes Permanente Creek Flood Protection Project Page 104 Planning Study Report July 2008 Criterion 1: floodplain -inclusion of appropriately sized floodplain Criterion 2: active channel -appropriateness of size and configuration of active channel Criterion 3: stable side slopes -stability of side slopes Criterion 4: transitions -stability of channel's inteclration with upstream and downstream reaches Objective 4: minimize maintenance requirements Criterion 1: structural features -maintenance ass~~ciated with structural features Criterion 2: natural processes -maintenance associated with vegetation, erosion and sediment Criterion 3: urban flows -maintenance resulting from small storms and outfall flows Criterion 4: access -incorporation of adequate access for maintenance crews and equipment Objective 5: integrate within watershed Criterion 1: meets watershed goals -ability to meet watershed goals as defined in a process that examines the watershed as a whole Objective 6: protect the quality and availability of wafer Criterion 1: water availability -impact on groundwater recharge Criterion 2: instream water quality -water quality protected through vegetation and instream hydraulic complexity Criterion 3: offstream water management -ability to enhance water supply and quality and reduce peak flows through local retention of rainfall Criterion 4: flow regime -ability to maintain geomorphically and biologically appropriate range of flows Objective 7: cooperate with other local agenciE~s to achieve mutually beneficial goals Criterion 1: mutual local goals -ability to achieve project-specific goals and objectives developed jointly by the District and local agencies: Criterion 2: supports general plan -ability to supp~~rt goals and policies as stated in general plans of partner agencies Objective 8: community benefits beyond flood protection Criterion 1: community safety -overall safety for appropriate access and recreation Criterion 2: recreation -quality of recreation experience provided by alternative Criterion 3: aesthetics -quality of aesthetic form provided by alternative Criterion 4: social and cultural benefits -opportunity to provide community involvement Criterion 5: local economic effects -potential effect on property values and/or local business climate Criterion 6: open space -inclusion of open space into alternative Criterion 7: community support -alternative reflects community developed objectives and ideas Objective 9: minimize life-cycle costs Criterion 1: net present value of lifetime costs Some of the criteria required comparative ratings between the alternatives (for example, which alternative has the least or the most cost) while otl-~ers were stand-alone ratings (for example, how well does the alternative meet community goals). Each alternative was rated as to how well it accomplished each criterion. A scoring system assigned various weights to the criteria and calculated the objective score (see Appendix F~ for NFP rating details) for each alternative. The result is a matrix (see Table 4.3: Feasible Alternatives Summary NFP Ratings) which shows a comparison of how well the alternatives rated on each of the nine NFP objectives. Permanente Creek Flood Protection Project Page 105 Planning Study Report July 2008 Community input was used to determine whether some NFP objectives should be considered more important than others. The Permanente Creek Task Force was asked to rate the nine objectives as to their relative importance: high, medium or low. The watershed manager approved the resulting rating, which is shown on Table 4.3. 4.7.3 Environmental Concerns The NFP objectives do not explicitly rate the environmental impacts of project alternatives. An alternative may rate very high even if it would have significant negative environmental impacts. Since environmental impacts are a significant factor in decision making, the project team developed criteria for rating feasible alternative environmental impacts. It was decided that the criteria for consideration should mirror the criteria that will be used later in the environmental impact report project analysis. Therefore, each alternative was rated on how well it avoided impacts for the following categories: Hydrology and Water Quality Biological Resources Cultural Resources Aesthetics Traffic/Utilities Noise Air Quality Health and Safety Recreation Each alternative was rated on each criterion and an environmental impacts objective rating was calculated (see Appendix F). 4.8 Staff Recommended Alternative Selection The staff recommended alternative was selected based on a comparison of the NFP ratings of all the alternatives (see Tables 4.3 and 4.4) as follows: The nine NFP objectives were rated as High, Medium or Low by District staff and the Task Force committee (Task Force ratings were used upon approval of the watershed manager). Alternatives A, D, E, and U were rated "unacceptable" in one or more "high" rank objective(s). Due to this, these alternatives were therefore considered to be unfit for selection as the staff recommended alternative. Alternative T requires extensive impacts to the mature oak trees existing on the South and West portions of the Cuesta Park Annex. Both the community and the District strongly oppose significant impacts to this area; therefore, this alternative was eliminated from consideration as the staff recommended alternative. The remaining seven alternatives were compared to each other (see Table 4.4). Alternatives G and V rank best for one objective (cost), though this is deceptive since the mitigation costs of the dam alternative are very difficult to calculate and have been neglected up to this point. Alternative Z is very close in its cost rating, with the cost being more reliable, since it does not include the dam project element. Permanente Creek Flood Protection Project Page 106 Planning Study Report July 2008 Alternatives S, Y, and Z tie for best ranking for twc- objectives (ecological functions and integration within the watershed context), chiefly because they are the three alternatives out of the seven that do not include the dam project element. Alternative Z also ranks best in terms of avoiding environmental impacts, because it is the only alternative that does not include the dam and also only impacts the Annex portion of Cuest~- Park. So, comparing alternatives G, S, V, Y and Z, alternative Z stands out because: • Impacts: Alternative Z would avoid impacts at the Cuesta Park parking lot area, which would include removal of approximately 100 park trees. • Ecological Functions: Alternative Z does not include the dam project element. • Cost: second best rating on cost, does not suffer from the uncertain costs of the dam project element. • Early flood protection: second best in te~•ms of post CSC Phase 1 number of parcels protected from one-percent flooding. • Technical feasibility: all project element~~ are simple and technically unambiguous; the lack of the dam project element means project design would be straightforward. Thus, using the NFP process, Alternative Z is, on I~alance, the best of the proposed project's feasible alternatives. 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L O Table 4.2 -Summary o-f Feasible Alternatives Alternative: A D E G S T Hale and Permanence Creek Flow detention at Hanson Flow detention at Cuesta park Annex and Park Flow detention at Cuesta bypasses around natural Hale and Perm.snente Creek dam, Rancho San Antonio, , and Rancho San Antonio park Annex and McKelvey No new construction; channel; Floodwalls d/s of bypasses around natural and McKelve Park; Hale y , McKelvey Park; Permanente Park; Permanente and Hale Alternative continue current Hwy 101; Concrete channel enlargement; EI Camino channel; Floodwalls d/s of Hwy 101; Concrete channel Creek b ass; concrete YP and Hale Creek bypasses; Creek bypasses; concrete l t l eSCCIptIOn: maintenance; monitor and in concrete l culvert bypass; EI Camino enlargement; EI Camino f channel enlar ement; 9 loodwalls d/s of Hwy 101; concrete channel ement; floodwalls d/s f enlar en argemen ; channe loodwalls d/s of Hwy 101; g rep ace ag channels as needed culvert enlargement; EI culvert bypass; EI Camino new diversion structure; g of Hwy 101; new diversion new diversion structure; Camino flood collection f lood collection channel; New optional concrete channel structure; optional concrete optional concrete channel channel; New diversion diversion structure removal and revegetation channel removal and removal and revegetation structure u-r -- - - Dam maintenance and Maintenance of detention Maintenance of detention New culverts designed with New culverts designed with upkeep; maintenance of detention pond inlets and and inlets and outlets; P and inlets and outlets; P Concrete channel adequate slope for sediment adequate slope. for sediment outlets; bypass designed asses desi ned with bYP 9 b asses desi ned with YP 9 maintenance; existing passage; concrete channel passage; concrete channel with adequate slope for adequate slope for sediment adequate slope for sediment Operation & sediment removal and maintenance; existing maintenance; existing sediment passage; concrete assa e; concrete channel P 9 i i assa e; concrete channel P 9 existin nce i t vegetation maintenance; sediment removal and sediment removal and channel maintenance; st n maintenance; ex 9 ; ma n ena g Maintenance: trash and debris removal; vegetation maintenance; vegetation mar ~tenance; existing sediment removal sediment removal and sediment removal and bank erosion repair in natural trash and debris removal; trash and debris removal; and vegetation maintenance; vegetation maintenance; vegetation maintenance; channels bank erosion repair in natural bank erosion rf:pair in natural trash and debris removal; trash and debris removal; trash and debris removal; channels channels bank erosion re air in natural P bank erosion re air in natural P bank erosion repair in natural channels channels ~r~ channels Socio-Cultural Environment: Acquisition of dam (A) Land Ownership/ Easements required from Easements required from innundation area and access y Easements from Cit of Mtn. Easements from City of Mtn. Access/ Right of None needed City of Mtn. View and Los City of Mtn. Vic:w and Los d i t l C l easements; easements from View, County, and one View and one private Altos, Caltrans, and private va trans, an pr e a A tos, City of Mtn. View, County, private property property yya y property owners property owners and one private property up to 4 ft high concrete up to 4 ft high concrete up to 4 ft high concrete up to 8 ft high concrete up to 8 ft high concrete floodwall heights built. floodwall heights built. floodwall heights built. (B) Aesthetics: current values maintained floodwall heights built floodwall heights built Potential for concrete Potential for concrete Potential for concrete channel restoration channel restoration channel restoration (C) Recreation Potential for extending Potential for extending Potential for e>tending Potential for extending Potential for extending Potential for extending h f T il Permanente Trail south of Permanente Trail south of Permanente Trail south of Permanence Trail south of Permanente Trail south of o Permanente ra sout POtentlal: Old Middlefield Road Old Middlefield Road Old Middlefield Road Old Middlefield Road Old Middlefield Road Old Middlefield Road Physical Environment: Current sediment removal Current sediment removal (A) Sedimentation: Current sediment removal Current sediment removal Current sediment removal activities would continue activities would continue Current sediment removal ti i i ld i activities would continue activities would continue activities would continue somewhat reduced due to somewhat reduced due to nue es wou con act v t reduced flows reduced flows Sites of potential concern Sites of potential concern Sites of potential concern Sites of potential concern Sites of potential concern Sites of potential concern (B) Water Quality: were considered of moderate were considered of moderate were considered of moderate were considered of moderate were considered of moderate were considered of moderate risk or lower risk or lower risk or lower risk or lower risk or lower risk or lower Site-specific geotechnical (C) Geology and Site-specific geotechnical Site-specific geotechnical analysis would be Site-specific geotechnical Site-specific geotechnical SOIIS: n/a analysis would be conducted analysis would be conducted conducted. Dam area would analysis would be conducted analysis would be conducted rr be extensively studied. Environmental ^r Review: Dam site located in (A) Biological bypass inlet locations in bypass inlet Iccations in undisturbed upland habitat. Detention ponds and bypass Detention ponds and bypass d i i i i l l n/a Other detention ponds and inlets located in ri arian P ar an n r n ets ocate P ReSOUCCeS' riparian habitat areas riparian habitat areas bypass inlets also located in habitat areas. habitat areas. rinarian hahitat areas. project elements involve Project elements involve Project elements involve Project elements involve Project elements involve disturbace to native disturbace to native disturbace to native (B) Cultural n/a disturbace to native disturbace to native undisturbed soils in bypass undisturbed soils in bypass undisturbed soils in bypass Resources undisturbed soils in bypass undisturbed s~~ils in bypass and flood detention and flood detention and flood detention excavation areas excavation arf;as excavation areas excavation areas excavation areas Bypasses constructed under Bypasses constructed under Bypasses constructed under Bypasses constructed under Bypasses constructed under (D) PUbIIC Services, none active roadways and utility active roadways and utility active roadways and utility active roadways and utility active roadways and utility Utilitites and Traffic corridors. corridors. corridors. corridors. corridors. Project Costs: Capital Costs: $o $118 million $121 million $50 million $67 million $68 million Maintenance Costs: $2s million $27 million $27 million $30 million $21 million $22 million Total PCOjeCt Cost: $29 million $145 million $148 million $83 million $92 million $93 million CSC Capital Cost: n/a $59 million $62 million $32 million $41 million $29 million Notes: All costs in 2008 $. Maintenance costs are for 50-year project life. 111 8/6/2008 Alternative: U V W X Y Z Flow detention at Hanson Flow detention at Hanson Flow detention at Hanson Flow detention at Cuesta Flow detention at Blach Flow detention at Hanson dam, Rancho San Antonio, dam, Cuesta Park Annex, dam and Cuesta Annex and Park Annex and Park, Blach School and Rancho San School, Rancho San dam and Rancho San and Cuesta Park Annex; and McKelve Park; Y Park; Permanente and , Antonio; Permanente and Antonio, Cuesta Annex, and Alternative Antonio; Hale Creek bypass; extended Hale Creek Permanente and Hale Creek extended Hale Creek extended Hale Creek McKelvey Park; Hale Creek DeSCrl tlOn: concrete channel bypass; concrete channel enlar 9ement; floodwalls d/s bypasses; concrete channel enlar ement floodwall d/ bypasses; concrete channel l fl bypasses; concrete channel b ypass; concrete channel p enlargement; floodwalls d/s g ; s s en argement; oodwalls d/s enlargement; floodwalls d/s enlargement; floodwalls d/s of Hwy 101; new diversion of Hwy 101; new diversion of Hwy 101; new diversion of Hwy 101; new diversion of Hwy 101; new diversion of H 1 T^'Y Ot; new diversion structure; EI Camino b ass YP structure; optional concrete structure; optional concrete structure: optional concrete structure; optional concrete structure; optional concrete channel removal and channel removal and channel removal and channel removal and revegetation revegetation reve elation g channel removal and revegetation revegetation Dam maintenance and Dam maintenance and Dam maintenance and Dam maintenance and upkeep; maintenance of upkeep; maintenance of upkeep; maintenance of upkeep; maintenance of Maintenance of detention Maintenance of detention detention pond inlet and detention pond inlets and detention pond inlets and detention pond inlet and Pond inlets and outlets; pond inlets and outlets; outlet; bypasses designed outlets; bypass designed outlets; bypasses designed outlet; bypasses designed bypasses designed with bypass designed with O eration & p with adequate slope for with adequate slope for with adequate slope for with adequate slope for adequate slope for sediment assa e concret h l adequate slope for sediment sediment passage; concrete sediment passage; concrete sediment passage; concrete sediment passage; concrete g p ; e c anne passage; concrete channel AAaintenance: channel maintenance; channel maintenance; channel maintenance; channel maintenance; maintenance; existing maintenance; existing existing sediment removal existing sediment removal existing sediment removal existing sediment removal sediment removal and sediment removal and and vegetation maintenance; and vegetation maintenance; and vegetation maintenance; and vegetation maintenance; vegetation maintenance; vegetation maintenance; trash and debris removal; trash and debris removal; trash and debris removal; trash and debris removal; trash and debris removal; trash and debris removal; bank erosion repair in natural bank erosion repair in natural bank erosion repair in natural bank erosion repair in natural bank erosion repair in natural bank erosion repair in natural channels channels channels channels channels channels Socio-Cultural Environment: (A) Land Ownership/ Acquisition of dam Acquisition of dam Acquisition of dam Acquisition of dam Easements from C t E innundation area and access innundation area and access innundation area and access innundation area and access oun y, asements from Los Altos Access/ Right of easements; easements from easements; easements from easements; easements from easements; easements from City of Mtn. View, Los Altos School District, City of Mtn. way. County and one private County and City of Mtn. View City of Mtn. View and one City of Mtn. View and one School District, and one View, County, and one ro ert P P Y and one rivate roe P~ P P rtY rivate ro ert P P P Y private property private property private property up to 4 ft high concrete up to 4 ft high concrete up to 4 ft high concrete up to 4 ft high concrete up to 4 ft high concrete (B) Aesthetics: up to 5 ft high concrete floodwall heights built. floodwall heights built. floodwall heights built. floodwall heights built. floodwall heights built. floodwall heights built Potential for concrete Potential for concrete Potential for concrete Potential for concrete Potential for concrete channel restoration channel restoration channel restoration channel restoration channel restoration (C) Recreation Potential for extending Potential for extending Potential for extending Potential for extending Potential for extending Potential for extending Potential: Permanente Trail south of Permanente Trail south of Permanente Trail south of Permanente Trail south of Permanente Trail south of Permanente Trail south of Old Middlefield Road Old Middlefield Road Old Middlefield Road Old Middlefield Road Old Middlefield Road Old Middlefield Road Physical Environment: Current sediment removal Current sediment removal Current sediment removal Current sediment removal Current sediment removal Current sediment removal (A) SedlmentatlOn' activities would continue activities would continue activities would continue activities would continue activities would continue activities would continue somewhat reduced due to somewhat reduced due to somewhat reduced due to somewhat reduced due to somewhat reduced due to somewhat reduced due to reduced flows reduced flows reduced flows reduced flows reduced flows reduced flows (B) Water QUallty: Sites of potential concern were considered of moderate Sites of potential concern were c id d f d Sites of potential concern i Sites of potential concern Sites of potential concern Sites of potential concern ons ere o mo erate were cons dered of moderate were considered of moderate were considered of moderate were considered of moderate risk or lower risk or lower risk or lower risk or lower risk or lower risk or lower (C) Geology and Site-specific geotechnical anal i ld b Site-specific geotechnical l i Site-specific geotechnical Site-specific geotechnical ys s wou e ana ys s would be analysis would be analysis would be Site-specific geotechnical Site-specific geotechnical SOIIS' conducted. Dam area would conducted. Dam area would conducted. Dam area would conducted. Dam area would analysis would be conducted analysis would be conducted be extensively studied. be extensively studied. be extensively studied. be extensively studied. Environmental Review: Dam site located in Dam site located in Dam site located in Dam site located in (A) Biological undisturbed upland habitat. undisturbed upland habitat. undisturbed upland habitat. undisturbed upland habitat. Detention ponds and bypass Detention ponds and bypass Resources: Other detention ponds and Other detention ponds and Other detention ponds and Other detention ponds and inlets located in riparian inlets located in riparian bypass inlets also located in bypass inlets also located in bypass inlets also located in bypass inlets also located in habitat areas. habitat areas. rinarian hahiTat areas rinarian habitat areas rinarian hahitat areas rinarian habitat areas Project elements involve Project elements involve Project elements involve Project elements involve Project elements involve Project elements involve (B) Cultural disturbace to native disturbace to native disturbace to native disturbace to native disturbace to native disturbace to native Resources undisturbed soils in bypass undisturbed soils in bypass undisturbed soils in bypass undisturbed soils in bypass undisturbed soils in bypass undisturbed soils in bypass and flood detention and flood detention and flood detention and flood detention and flood detention and flood detention excavation areas excavation areas excavation areas excavation areas excavation areas excavation areas (D) Public Services, Bypasses constructed under Bypasses constructed under Bypasses constructed under Bypasses constructed under Bypasses constructed under Bypasses constructed under Utilitites and Traffic active roadways and utility active roadways and utility active roadways and utility active roadways and utility active roadways and utility active roadways and utility corridors. corridors. corridors. corridors. corridors. corridors. Project Costs: Capital Costs: $69 million $47 million $56 million $63 million $66 million $58 million Maintenance Costs: $29 million $29 million $31 million $29 million $21 million $22 million Total Project Cost: $102 minion $79 million $90 million $96 million $90 million $84 million CSC Capital Cost: $51 million $37 million $29 million $44 million $55 million $40 million Notes: All costs in 2008 $. Maintenance costs are for 50-year project life. 112 0 0 N .~ ~-+ ._ ~-+ ^V W ^.^^~ ~i~i /O 6i Z ^V/ `W ^~ ~~ L a a~ 1 M N ~ ~ ', cj „l- A "~ Q X ~ ~~ , ~ r ~ ~ .~ '~ ~ ~ ~ ~ rc~• } ,, ~j Q ~ U') Q ~ ~ ~ ~ p ~ ~ ~~ r~ ~x~ ~ ~~ Q Q ~ ~~ T s C11 ~..n Cb ~ N N ~ i7, __ 1 ~ ~ ' Z ~ '~ ~,r~ ~ r ~. "' S~ - ~~. - t6 T:' ... ~~~ _ O ~ _. ._. - r.. _~ _. ` r_ a~ ~ ~) -~ ~, u - _ ~ . ~ `T~ ~ o ~ ~, ~ `r c _ ~ z N ~ '~ „ (~ Q) ~ --~ - _ r ) ~ Q> ~ C Q r_~ - L' ~ Q~ _C ~ ? O N - ~ ~ G.. 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Q) itt ~ ci7 ~ r~ ~. ~ ~ ~ I ~U ~ ~ _O ~ S] to s } ~ ~ i ~~ s ~ ' '~ € t~ ?. ~ ' ° _ ~G n cr ~ ~ N ' ~ .~ Q) ~ .~ ~ U n~ . y 1 _, ,« V p n ~, n c_ ~ ~ - ~ p r~ a , ° ~ _ ~n ~ -~ .~ ~ ~ ~ 0 2 a> ~ ~ ~ o ~: iJ a a) ~ ~ ~ 2' ~ cCS ~ -~ ~ O W C7.. y ~ ~ ~ N N ~ ~ ~ ~ O N ~ N € ~ .-~ 4. ,~ N O (ll Q rn ~ U ~ _ ~ ~ ~ N ~ U (ll ~ Qi cn ~ ~ -CS ~ r ~ - q g ~ ~ ~ r O ~ ~ fl` U ~ f , -` ' ~ j 'I ~ O ~ n ri! ~ i p ~ 11.. -+ _ ir, ~, i i:+ U N 0 a~ 0 w d .c a~ +. m N N w a~ .. a N CN G 0 rn ca Y N u E a~ E 0 Y C ccS U N a~ 0 ~~7 ~ J .. Q N .ro o ~ ~` a ~ a a~ v U RS C • ~ V ~ ~ ~ RS i N ~ ~ ~ Q T Y m C cLS r rn cu ca m 6 7 CHAPTER 5 PROJECT OUTREACH Throughout the planning process, outreach activities have been carried out to inform the public of project progress and solicit public feedback. Several public meetings were held at crucial milestones along the planning process. A citizen's task force committee was set up early in the planning process to provide focused review and discussion. Finally, specific outreach activities have been conducted with local groups, environmental groups, and resource agencies. 5.1 Public Meetings Public meetings were held at all crucial project milestones. In each case, the public was invited to the meetings through a letter mailed to all property owners and residents living adjacent to the creeks or in the Permanente Creek one-percent floodplain. • Problem definition and initial project scoping meeting (January 2002): this was the kickoff meeting for the project and the public attendees heard about project objectives and the preliminary planning schedule. • Refined problem definition and potenti~~l alternatives meeting (March 2003): this meeting covered the one-percent flood dei~inition and discussed some of the potential alternatives arising from the special characteristics of Permanente Creek watershed. This was also the meeting in which the Permanente Creek Task Force was initially recruited. • Conceptual Project Elements town hall meetings (June 2004): a series of four meetings were held at community locations dispersed along the watershed. The initial 17 CPEs were discussed with the public and feedback/comments were solicited. • Conceptual alternatives meeting (November 2004): The conceptual alternatives, consisting of various combinations of CPEs were discussed with the public and feedback/comments were solicited. • Feasible alternatives meeting (May 200;0: The feasible alternatives, including the most highly ranked alternatives according 'to the NFP objectives rating were discussed and public feedback/comments were sought. 5.2 Permanente Creek Task Force A task force composed of public volunteers and members of the city staff of Mountain View and Los Altos was established in 2003. The aim of thE~ Task Force was to be a smaller representative of the general public and city staff. Such a Task Force would allow more frequent meetings to be scheduled and more meaningful and detailed comments and concerns could be collected. The Task Force was composE~d of Mountain View and Los Altos citizens, city staff from Mountain View and Los Altos, and C~istrict staff. The Task Force roster can be seen on the acknowledgements section of this report. Permanente Creek Flood Protection Project Page 117 Planning Study Report July 2008 Task Force meetings were held at the following dates: • June 2003: Task Force set up • October 2003: Field trip to look at various watershed features and potential project element locations • March 2004: CPE introduction meeting • September 2004: Conceptual alternatives • March 2005: More refined conceptual alternatives • July 2005: More refined conceptual alternatives • February 2006: Initial meeting on feasible alternatives • July 2006: Feasible alternatives and project selection process • July 2007: Staff recommended alternative The Task Force provided invaluable assistance and feedback throughout the planning process. The project team would like to especially thank Task Force member John Benza of the First Baptist Church of Los Altos for his generous help in providing a wonderful meeting location (at the church). 5.3 Outreach to Cities and County As the planning process progressed, meetings were held with the various affected local jurisdictions. These meetings were opportunities to discuss potential project benefits and impacts with the cities and collect early feedback and comments. • January 2007: Mountain View City Council workshop • March 2007: Cupertino City Council presentation • March 2007: Los Altos City Council presentation • March 2007: County of Santa Ctara Board of Supervisors presentation • May 2007: Project scoping meetings in Los Altos and Mountain View • February 2008: Mountain View City Council workshops (two meetings) • April 2008: Los Altos City Council presentation Further outreach will continue, culminating in the official CEQA process. Permanente Creek Flood Protection Project Page 118 Planning Study Report July 2008 5.4 Resource Agencies Various resource agency permits will be required to be obtained by the project prior to construction. Therefore, in order to improve the ~~roject and expedite future review, early meetings were held with the various resource agE~ncies in advance of the CEQA process. The project team met with the resource agencies in Aragust 2004 to discuss general project issues. This was followed in July of 2006 with a discussion of the feasible alternatives. Generally, the agencies have been supportive of the NFP decisi~~n making process. They pointed out that the upper watershed area contains valuable habitat and may contain endangered species such as the California Red-Legged Frog. They therefore Expressed serious concern regarding the Hanson Dam project element. 5.5 Meetings With Watershed Stakeholders The project team has conducted wide-ranging outreach with various environmental and civic stakeholders in the project area. This effort was undertaken to inform the stakeholders of the project and its progress and to solicit early feedback. Some of the organizations contacted include: • Stevens and Permanente Creek Watersheds Council (SPCWCr two presentations have been made to the SPCWC. They have been keenly interested in the project. A particular interest of the group is the restoration of the connection between Permanente Creek and Stevens Creek through the restoration of the Permanente Diversion. • Save Open Space (SOS): Save Open Sp~~ce has taken a very active role in the project. Their particular concern regards the Cuesta Park Annex. SOS played a very active role during the City of Mountain View's concep~lual planning of the Annex site in 2006, supporting the eventual City Council selec~lion of "Concept B" for the Annex. Later, as the District continued outreach activities and indicated staff would be very willing to work with SOS to develop a more detailed vision of the Annex with flood detention as an added element, SOS assisted the District': consultant with designing the Annex area. SOS has supported the project at meetings with the Cuesta Park Neighborhood Association and at Mountain View City Corancil meetings. • Mountain View Chamber of Commerce 1'MV000r Meetings were held with the MVCOC in December 2006 and February ?007. The MVCOC has been supportive of efforts to protect Mountain View residential and business areas from flooding. • Blach Junior High School: an initial meei:ing was held with the school in August 2007. The school expressed strong concern reg2~rding losing the football field and track area for extended periods of time. The design concept was changed to minimize the construction period required, thus reducing the instructional impact to Blach students. Follow-up meetings will be held once better visual renderings of the site are available for discussion. • Gate of Heaven Cemetery. The cemetery is immediately adjacent to the Rancho San Antonio flood detention site. A meeting was held with cemetery staff in August 2007. The cemetery expressed concerns regarding impact to water wells located in the proposed detention pond area and impacts to their property access. The water wells will be relocated to another appropriate site prier to excavation of the pond site and a new Permanente Creek Flood Protection Project Page 119 Planning Study Report July 2008 bridge will be built over the creek improving the cemetery's access to maintenance buildings to the west of the creek as part of the Rancho San Antonio project. Community for Green Foothills: a presentation was provided in December 2007. Also present at the meetings were attendees from the Audubon Society. There were concerns raised about entraining fish in bypasses and detention sites. There was interest expressed at restoration opportunities for the concrete lined channels. Hanson Permanente Cement Quarry. Various meetings have been held with the Quarry. A geophysical investigation of the potential dam area was conducted in 2006. Habitat and wetlands mapping work was also conducted at this time. Permanente Creek Flood Protection Project Page 120 Planning Study Report July 2008 CHAPTER 6 RECOMMENDED PROJECT The design basis, recommended project elements, and construction procedures are described in this chapter. See Appendix H (bound separately) for the engineering drawings of the recommended project. A description of the maintE~nance guidelines for the recommended project is provided in Chapter 7. 6.1 Design Basis The overall design basis for the recommended alternative is to utilize four off-stream flow detention alternatives in order to reduce the peak design flows sufficiently so that very little channel improvement work is necessary downstream of EI Camino Real. The detention basins at Rancho San Antonio Park, Blach School, and C;uesta Park Annex reduce the peak flows in Permanente Creek by 34 cros (1200 cfs) and the detention basin at McKelvey Park would reduce the peak flow from Hale Creek by 11 cros 1;400 cfs). With those elements in place, the only downstream improvements needed for flood protection would be floodwalls along Reach P2. Table 6.1 provides a comparison of th~~ pre-project versus post-project design flow situation for the various watershed reaches. Table 6.1 -Design Flows Pre- and Post-Project (cros/cfs) Pre-Pr~~ject Post- Project Location: 1 % 10% 1 % 10% Rancho San Antonio: 48 / 1700 27 / 950 28 / 1000 27 / 950 C~ Permanente Diversion: 76 / 2700 42 / 1500 57 / 2000 42 / 1500 Downstream of Blach School: 40 / 1400 31 / 1100 40 / 1400 40 / 1400 Permanente u/s of Hale: 40 / 1400 14 / 500 6 / 200 6 / 200 Hale u/s of Permanente: 31 / 1100 19 / 670 No Change Permanente d/s of Hale: 65 / 2300 27 / 950 25 / 900 25 / 900 Permanente Reach P3 71 / 2500 31 / 1100 31 / 1100 31 / 1100 Permanente Reach P2 74 / 2600 34 / 1200 34 / 1200 34 / 1200 As can be seen, the general effect of the flow detention sites would be to reduce the one- percentflow to approximately the level of the 10-percent flow. 6.2 Recommended Project 6.2.1 Floodwalls (Reach P2 and PD) With 1 percent flows reduced to 34 cros (1200 cfs) due to upstream flow detention, the design water surface would be below the current levee elE~vations along most of the reach. However, the FEMA and District freeboard requirement of 1.:? meters (4 feet) would not be met for most of the levee channels of Reach P2. Thus, a concrete floodwall would be built on top of the existing levees, bringing the top of bank up to the required freeboard elevation. The downstream end of the floodwall protection would be in the high grounds of the Shoreline Park. These same highlands will most likely be used as part of the Bay Levee being currently studied by the U.S. Permanente Creek Flood Protection Project Page 121 Planning Study Report July 2008 Army Corps of Engineers. Thus, when the Bay Levee is completed, seamless tidal flood protection would be provided. Previous geotechnical investigations have indicated that the existing levees are generally in good condition. The floodwall work would begin approximately 120 meters (400 feet) north of Amphitheater Parkway and continue for about 850 meters (2800 feet) upstream to Highway 101. The floodwall heights would range from zero (where levee freeboard is adequate) to a maximum of approximately 1.2 meters (4 feet), with an average elevation of .6 meters (2 feet). Typical construction procedures would include trench excavation, form work installation, concrete pouring, backfill, and aesthetic texturing on the exposed faces of the floodwall. Please see Figure 6.1 for a rendering of the floodwalls and Appendix H for detailed plans and sections. Maintenance procedures would include weed and graffiti control and repair/replacement of the wall, as needed. To address the prospect of long-term sea level rise, the foundations of the floodwalls would be designed such that the walls could be raised by up to 0.6 meters (2 feet), as needed. Approximately 200m (650 ft) of floodwalls would also be needed in Reach PD just upstream of the Blach School area. The water surface in this area is slightly above adjacent ground and therefore a floodwall with the required freeboard is needed to provide adequate protection for adjacent properties. Please see Appendix H for plans and sections. 6.2.2 Riparian Restoration (Reach P3) With 1 percent design flows reduced to 31 cros (1100 cfs) in Reach P3, it would be possible to replace the aging concrete channels along the downstream 700 meters (2300 feet) of Reach P3 (between Highway 101 and Middlefield Road) with a partially natural channel, while extending an existing pedestrian trail. This project element is not needed as a flood protection element; this element provides an opportunity for environmental enhancement and public trail extension, at the District Board's discretion. The construction procedure would be as follows. The existing concrete channel would be removed. Anew concrete bank would be built at'/z:1 side slope on the east side of the channel. An earth bankfull channel would be built sized to carry the 1.5-year flow (approximately 5 cros or 180 cfs), with a vegetated floodplain and vegetated bank on the west side of the channel. At every 0.15 meter (1/2 foot) rise in the invert, a rock riffle invert stabilization structure would be built. A 3.7 meter wide (12 foot) combination pedestrian/maintenance trail would be built on the concrete bank side of the channel, with a safety railing built into the concrete lining's top. Please see Figure 6.2 for a visual rendering of this project element and Appendix H for detailed plans and sections. Maintenance required would include weed and graffiti control for the trail and concrete bank, bank repair for the natural bank as needed over time, and vegetation maintenance (limited to removal of hazard trees and control of invasive non-natives) in the vegetated section. Permanente Creek Flood Protection Project Page 122 Planning Study Report July 2008 Figure 6.1. Floodwalls (Note that the lower floodwall elevation would be used) Permanente Creek Flood Protection Project Page 123 Planning Study Report July 2008 Permanente Creek -Existing View North of Hwy 101 Permanence Creek - North of Hwy 101 with 7-foot Floodwall Concept Permanente Creek -North of Hwy 101 with 3-foot Floodwall Concept ~•.f ~S_. N Figure 6.2. Riparian Restoration and Trail Extension Permanente Creek Flood Protection Project Page 124 Planning Study Report July 2008 Permanente Creek -Existing View Looking North from Middlefield Way Permanente Creek -Future View with Channel Restoration Concept 6.2.3 Channel Widening (Reach P5) The work involves deepening and enlarging the current concrete channel from just upstream of Park Drive to upstream of the confluence with Hale Creek. This work would replace the most degraded part of the concrete channels built in the 1960s, thus addressing the most urgently needed part of the concrete channel restoration. It would also increase channel capacity upstream of McKelvey Park so that the full one-percent flows can reach the McKelvey Park flood detention site. The Mountain View Avenue bridge invert would be lowered by approximately 0.6 meters (2 feet). The bridge structure itself would not be removed; rather, the invert would be excavated and a new U-frame concrete channel would be built inside the bridge structure. Due to the very limited right-of-way available and the deteriorated condition of the existing channel, temporary shoring would be needed prior to removal of the existing channel. The new channel built would lower the invert upstream of Park Drive by eliminating the drop structure located there currently. The upstream grade would be steepened so that it would conform to existing invert at the Hale Creek confluence. The 24-inch RCP outlet pipe for McKelvey would be built alongside the new channel during the channel construction. See Appendix H for engineering drawings of the work and several typical sections. Maintenance requirements would include graffiti control and typical long-term maintenance of the concrete channel. 6.2.4 Channel Widening (Reach H1) This work involves increasing the capacity of some sections of reach H1, which currently do not have full one-percent capacity. The sections are: • Mountain View Avenue Bridge • Channel reach from Mountain View Avenue to Arroyo Drive • 7th Day Adventist Bridge • Channel section from 7th Day Bridge to North Sunshine Drive • North Sunshine Drive Bridge • Channel section from North Sunshine Drive to South Sunshine Drive • Channel section from South Sunshine Drive to Springer Road • Springer Road Bridge • Channel section from Springer Rd to private bridge at 400 Springer Road • 400 Springer Road Bridge • Cuesta Drive Bridge • Channel section from Cuesta Drive to Arboleda Avenue • Arboleda Avenue Bridge • Channel section from Arboleda Avenue to Rosita Avenue (including four private bridges) The portions needing to be designed and built to meet CSC commitments of flood protection north of EI Camino Real are the first two bullets only. The remainder of the work would be needed for full flood protection in the upper watershed. The proposed work would involve deepening and steepening the channel through elimination of drop structures upstream of several of the bridges mentioned above. The existing concrete trapezoidal channels, which are worn and require repair or replacement soon, would be removed and replaced with a new concrete trapezoidal channel to the 10-percent flood elevation (approximately 1.2 meters or 4 feet deep) with 1:1 side slopes. The top of the channel Permanente Creek Flood Protection Project Page 125 Planning Study Report July 2008 would be lined with rip-rap protection to the top of bank. In areas where the existing access ramps create poor hydraulic conditions due to large expansion/contraction losses, the channel would be rebuilt such that the ramp area is blocked off the creek channel except during actual maintenance operations. See Appendix H for engineering drawings of the work and several typical sections. Maintenance requirements would include graffiti control and typical long-term maintenance of the concrete channel. 6.2.5 Hale Creek Bypass Since the existing natural channel along Reach H2 cannot pass the full one-percent flowrate and it is undesirable and environmentally damaging to disturb the natural creek channel by expansion and steepening, a bypass channel is proposed to span the low flow section of the creek. The design and construction of this project elemenf is not required to meet the projects CSC requirements for flood protection north of EI Camino Real. It would be needed to provide full flood protection in the upper portion of the watershed. The inlet structure would be built along the existing storm drain outlet pipe located at 1140 Riverside Drive (currently occupied by "Marti's Dance"). The City of Los Altos has a storm drain easement that could be used to accommodate the culvert. The inlet would be set at the 1.5-year flood elevation so that all low flows would continue down the natural channel. All flows greater than the 1.5-year flow event would be split between the natural channel and the culvert. The culvert would be 2.4-meters wide by 2-meters high (8 feet X 6.5 feet) and 1130 meters (3700 feet) long from the inlet to the connection to the creek just downstream of Rosita Avenue. The path followed would be north on Riverside Drive, east on Covington Road, and south on Springer Road. See Appendix H for engineering drawings of the work and several typical sections. Maintenance requirements would include vegetation and sediment control at the inlet and typical long-term maintenance of the concrete culvert. Due to the adequate slope, the culvert would not likely have sediment maintenance issues. 6.2.6 McKelvey Park Flood Detention Approximately 74,000 cubic meters (60 acre-feet) of storage volume would be created in the 2 hectare (5 acre) site. The site would be excavated approximately 15 feet deep, with vertical sides (supported by retaining walls) in order to maintain the baseball field dimensions as existing. The parking lot area would be reconfigured such that it would slope down at 5 percent slope down to the new field level. There would be stairs down to field level placed at various points along the perimeter, as well as two handicapped accessible ramps at Park Drive and Miramonte Avenue. The restrooms and concession facilities would be built at existing ground level to protect from inundation during the flood events. The inlet and outlet would be located in the southwest corner of the property in the triangular parcel owned by the District. The weir inlet would be designed to spill at 25 cros (900 cfs), which is slightly lower (more frequent) than the 10-year frequency event. Thus, it is expected that the site would, on average, get flooded once every nine to ten years over a long period of time. The site would drain back to the inlet area stilling basin, where a 610 mm (24 inch) RCP would drain the site. The pipe would be installed parallel (and lower than) the replaced concrete channel downstream to Park Drive, where it could connect to the channel. This would also be the normal drainage outlet for rainfall and local inflow water. The site would drain completely in 1-2 days, depending on the flood event. Permanente Creek Flood Protection Project Page 126 Planning Study Report July 2008 Since the site sees heavy use almost all year, proper procedure for post-flood maintenance and cleanup would be crucial. A maintenance contract would be developed between the District, the City of Mountain View, and a maintenance company such that cleanup activities would be started immediately after any inundation event. Excess sediment would be scraped off the fields, any remaining sediment brushed or washed off, and the fields' dirt areas and lines restored. The retaining walls would be faced with decorative treatment (bricks or other) and maintained free of graffiti. See Figure 6.3 for a rendering of the site and Appendix H for engineering drawings and sections. Figure 6.3. McKelvey Park Visual Simulation of Possible Project Permanente Creek Flood Protection Project Page 127 Planning Study Report July 2008 ,.::_ . Existing View From the Left Field Line Looking South 6.2.7 Cuesta Park Annex Flood Detention Approximately 80,000 cubic meters (65 acre-feet) of storage volume would be created on the northern 2.5 hectares (6 acres) of the Cuesta Park Annex. The site would be excavated approximately 6.5 meters (20 feet) deep with variable gentle side slopes averaging 4:1. Various park features such as trails, picnic areas, a seasonal streambed, boulder outcrops, etc. could be built into the detention area. Ramps would be constructed at 5% slope to promote handicapped access to all features. The detailed features of the park would be determined during the design phase of the project in workshops with the community, city staff, and elected leaders. The inlet would be located at the southeast corner of the detention area, where the inlet pipe would open out into the seasonal streambed feature. The outlet would be into a 914 mm (36-inch) RCP pipe at the northwest corner of the site. Regular site drainage for rainwater and local groundwater inflow would also be through this outlet pipe. The outlet pipe would continue west down Cuesta Drive and north on Miramonte to Marilyn Drive, where it would continue west to meet Permanente Creek for a total length of approximately 1200 meters (3900 feet). The site would drain in 1-2 days, depending on the flood event. This site would receive the overflow flood flows from the Blach School detention area. Thus, only when the Blach School site would be full would this site be impacted, reducing the flood frequency to the 50-year or above events. Over time, the site would likely be inundated once every 50 years, on average. Post flood maintenance would include sediment removal and repair of any damaged paths, plants, or structures. See Figures 6.4, 6.5, and 6.6 for several renderings of what the site could look like and Appendix H for engineering drawings and sections. 6.2.8 Blach School Flood Detention and Permanente Bypass Approximately 80,000 cubic meters (65 acre-feet) of storage volume would be created on approximately 2 hectares (5 acres) of Blach Junior High School's football field and track area. The site would be excavated approximately 4.5 meters (15 feet) deep with 2:1 side slopes. All existing facilities (football field and track) would be restored at the bottom of the excavated pond area. Ramps would be constructed at 5% slope to promote handicapped access to all features. The detailed features of the park would be determined during the design phase of the project in workshops with the school, the community, and School Board officials. The inlet would be located on the south side of the parcel, adjacent to the District`s Permanente Diversion. The District would build an overflow weir spilling into a stilling basin, which would dissipate the fall energy and ensure even spread of flows into the detention area. The outlet would be into a 2.4 meter (8-foot) diameter RCP pipe on the north side of the site, which would be designed as another overflow weir (with a smaller opening at the bottom for normal drainage). Regular site drainage for rainwater and local groundwater inflow would also be through this outlet pipe. The outlet pipe (called the Permanente Bypass) would continue north under Thatcher Drive and Hospital Drive to Cuesta Park Annex for a total length of approximately 1200 meters (3900 feet). The site would drain in approximately one day, depending on the flood event. Permanente Creek Flood Protection Project Page 128 Planning Study Report July 2008 Figure 6.4. Cuesta Park Annex / - w4 C ~ ~ i `r ~yry aiaR... ~ '~ ~~ ~ti~ - .a _. iN'~ :: ~~`"&. r ~w n i r ~.f~ F d ~ t" T'M.>~a ~~ ``.~ ~ ..,~ i~ ~. ~` .. Y 1 + L ~~}i> ~ ~ Permanente Creek Flood Protection Project Planning Study Report ` g ~'`-.~1'S~T ,~r- r f _ ~f 1 ~~ ^~'i.. } ~ i 6v. ;... eTy ~t d :a` `~ F tr ..~~ Y ~ t `y` ~ ~ ' :- t 7 ~ 'w/ ! 1 Jy'7~'~ y'. G ~,~y~f~'~~~ ~~ `~ r~ S~~, !~ .Y^: _ ~ _ e^ Page 129 July 2008 2. View from Lookout p'.atfor rr along Cuesta Dnve. Looking south. Figure 6.5. Cuesta Park Annex ~:. .~' Cr-t Pi3• ~`~-~`'~ ~ Y ~-~~ ~-- ~. .. .3 ~' " ~: ~ 5 ~.. .~ ?; ~ a„ .- l` '~ t ~. v,e.ti~ a~a,g bas~~n ua~~• ~~~iu•~ Lounci~ Grcie ane ripa~ a~~ 3ie~ b r ~"F._ ~ -_ - . ... ~° ~;e. ~: ~1-` Permanente Creek Flood Protection Project Page 130 Planning Study Report July 2008 seen i^ lower right ~ookmg rr~ith•nest. Figure 6.6. Cuesta Park Annex .'~- ~ ~ ~.~ ~~~t . ~ ~: _. .~,~ ~," ~ -~ .~ ~,, :~: . . Ft h~ ' ti a, ~'~ %t !n upper let' _ocl.,~~~g >~-~~!tnFast Permanente Creek Flood Protection Project Planning Study Report Page 131 July 2008 -a Boardwalk m m~ddlegro~!rd ~;~rth museum building beyond. Existing parking lot ~s behind trees The overflow weir from the Diversion would be set at 40 cros (1400 cfs), which is equal to the current capacity of the channel at Blach School. Thus, the site would only begin flooding at the event that it would flood prior to the project. The only difference is that pre-project flooding would spread across the entire school grounds and the local neighborhood, while post-project flooding would be confined to the detention area only. 40 cros (1400 cfs) plus the 3 cros (100 cfs) continuing down the natural Permanente Creek channel is the 10% flow at this location. Thus, over a long period of time, the detention area would be flooded once every ten years, on average. Post flood maintenance would include sediment removal, restoration of the play fields to good condition, and repair of any damages. See Appendix H for engineering drawings and sections. 6.2.9 Rancho San Antonio Flood Detention Approximately 120,000 cubic meters (100 acre-feet) of storage volume would be created on approximately 3.5 hectares (8.5 acres) of Rancho San Antonio Park adjacent to the Gate of Heaven cemetery. The site would be excavated approximately 4.5 meters (15 feet) deep with variable natural side slopes. Native trees and other appropriate vegetation would be planted on the side slopes and the bottom of the detention area. A meandering low flow channel feature would be created both to promote wetland development and rainy season drainage. An existing natural gas line crossing the site would be clearly marked and avoided. Water wells and pipes serving the cemetery would be relocated to new sites slightly south out of the excavation area. The existing hiking trails would be realigned with the detention area. The inlet would be located southeast of the detention area along the creek, where a low flow crossing currently serves as access to the west side of the channel where the cemetery has various maintenance structures. The crossing would be rebuilt as an at grade culvert with the capacity of the culvert set at 28 cros (1000 cfs). Flows in excess of the design flow would spill into a side channel and get transmitted to the detention area through a pipe and swale. In order to ensure flows would be contained on the lower west bank of the creek, some of the excavated soil from the detention area would be placed on the west bank of the bridge and vegetated with native trees. This would confine flows to the appropriate path up to the one-percent event. The outlet would be through a 610 mm (24-inch) RCP pipe at the northwest corner of the site, which would drain to an outfall under the existing pedestrian bridge just south of the site. Regular site drainage for rainwater and local groundwater inflow would also be through this outlet pipe. Construction and haul access would be through existing access south along the creek to Stevens Creek Road. The access may need to be improved to tolerate truck traffic. Large equipment access will not be allowed from Cristo Rey Drive. The design spill event would be slightly higher than the 10% event; thus, over time, the site would likely be inundated once every 10 years, on average. Post flood maintenance would be limited to repair of any damaged paths, plants, or inlet/outlet structures. See Figure 6.7 for a rendering of what the site could look like and Appendix H for engineering drawings and sections. Permanente Creek Flood Protection Project Page 132 Planning Study Report July 2008 Figure 6.7. Rancho San Antonio ~.. a ..~.-. ~: ~ ,~.' ~-~ _ ~ ~"'~~ - ~~ ... 'ri'd'= C'- SY~ ..~.- t=r f w. Existing view from Cristo Rey Drive looking southwest il~E~.?A'.~._... •- Visual s ~+^' ~.:. e ,: ~~~. ~r:E! ~,. 4 ~, Visual Simulation Rancho San Antonio Pond ENVIRONMENTAL VISION Santa Clara County, California ~~~:~~, Permanente Creek Flood Protection Project Page 133 Planning Study Report July 2008 6.2.10 New Diversion Structure The existing diversion structure (at the upstream end of the Permanente Diversion) does not function correctly currently. The low flow intake was built into the invert of the channel and tends to silt up very quickly during winter flows. The diversion was modified later into an overflow weir parallel to the flow path; but that structure does not allow for low flows to continue down the natural Permanente Creek (Reach P7). Thus, the current flow profile at this location is that all flows, low and high, continue to Stevens Creek. The new diversion structure would be constructed with the following aims: Very low flows should flow into Reach P7; One-percent flow break should be 54 cros (1900 cfs) down Permanente Diversion and 3 cros (100 cfs) down Reach P7; and Since sediment issues cannot be avoided, good access to maintain the low flow capability in the winter season should be provided. The existing invert flow inlet would be filled in and the existing diversion structure removed. The new diversion structure would be protected by an overflow weir separating the main flow of the diversion from the flow to be routed to Reach P7 up to the full one-percent flow. This overflow weir would have aloes-flow opening in the bottom of it allowing all low flows (under the weir) to pass through to the new diversion structure. There would be a maintenance ramp off Miramonte Ave down to the invert of the vault protecting the new diversion structure to provide adequate maintenance access. A 1.2 meter (4-foot) diameter RCP pipe would connect the new diversion structure to the existing 1.4 meter (54-inch) diameter pipe connecting to Reach P7 downstream of Eastwood Drive. See Appendix H for engineering drawings and sections. 6.3 Right-of-Way Requirements The right-of-way required by the recommended alternative for each project element is detailed below (see Appendix H for plans): • F/oodwal/s: Portions of the floodwall length north of Highway 101 lie on City of Mountain View property. The District would need to acquire flood control easements for these areas. • Riparian Restoration: Portions of the right-of-way needed for this project element is currently owned by the City of Mountain View. The District would need to acquire flood control easements for these areas. • Channel Widening (Reaches P5 and H1): This work would take place entirely on existing District right-of-way. • Hale Creek Bypass: For the inlet location, a District easement would be needed covering the existing storm water utility easement owned by the City of Los Altos. Otherwise, for the main culvert portion under local streets, a temporary construction access easement followed by a long term maintenance agreement would be sought. Permanente Creek Flood Protection Project Page 134 Planning Study Report July 2008 • McKelvey Park Flood Detention: The inlet/outlet area is already District owned. A flood control easement covering the portions of the site used for flood storage would be sought to allow for long term site access and maintenance activities. • Cuesta Park Annex Flood Detention: A flood control easement covering the portions of the site used for flood storage would be sought to allow for long term site access and maintenance activities. • Bach School Flood Detention: A flood control easement covering the portions of the site used for flood storage would be sought to allow for long term site access and maintenance activities. • Permanenfe Bypass: For the main culvert portion under local streets, a temporary construction access easement followed by a long term maintenance agreement would be sought. • Rancho San Antonio Flood Detention: A flood control easement covering the portions of the site used for flood storage would be sought to allow for long term site access and maintenance activities. • New Diversion Structure: This work would take place entirely within existing District right-of-way. 6.4 Best Management Practices The District's Best Management Practices (BMP) handbook (District Document No. W751 M01) will be used during the construction activities. 6.5 Climate Change There is a potential for climate change and associated sea level rise to impact future flood protection for this project. Therefore, the project will use adaptive design to allow future modifications to increase channel capacity, as needed. Specifically, the floodwalls north of Highway 101 would be built with adequate foundations to allow raising the floodwall heights. Permanenfe Creek Flood Protection Project Page 135 Planning Study Report July 2008 Permanente Creek Flood Protection Project Page 136 Planning Study Report July 2008 CHAPTER 7 MAINTENANCE PROGRAM 7.1 Maintenance History Regular maintenance work has been conducted within the Permanente Creek watershed over the past few decades. This work can be divided into creek processes maintenance (sediment removal and vegetation control) and infrastructure replacement maintenance. 7.1.1 Historic Creek Processes Maintenance Due to the shearing effects of the highly active local fault zones, activities of the cement plant in the upper watershed, hydrologic effects due to urbanization, and tidal effects, sedimentation has long been a major issue in the watershed. As described in more detail in Chapter 3, significant sediment deposition has historically occurred at two locations in the Permanente watershed: (1) on Permanente Creek near Highway 101; and (2) in the Permanente Diversion and in Permanente Creek immediately upstream of the Diversion. Minor sedimentation problems also occur along Hale Creek and its tributaries. The significance of the sediment removal efforts can be shown by the volume of sediment removed from the watershed over time. Figures 7.1 and 7.2 show the sediment removal volumes at the two most significant locations over a long period. Figure 7.1 -Sediment Removal 1980 - 2000 Permanente Creek Downstream of Highway 101 4,500 4,000 3,500 3,000 2,500 2,000 E 1,500 a~ 1,000 500 0 Year Permanente Creek Flood Protection Project Page 137 Planning Study Report July 2008 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 Figure 7.2 -Sediment Removal 1983 - 1999 Permanente Diversion 9,000 8,000 7,000 M ~ 6,000 ... ~ 5,000 a~ E 4,000 v ~ 3,000 2,000 1,000 0 1983 1985 1987 1989 1991 1993 1995 1997 1999 Year Sediment removal at Permanente Diversion, which is by far the larger of the two sediment zones, is closely correlated with strong rainfall years. The two biggest sediment removal years were following the 1983 and 1998 EI Nino seasons. Sediment removal downstream of Highway 101 is mostly associated with tidal issues and therefore does not correlate with strong winter precipitation years. The average annual sediment removal at the Diversion is 1840 cubic meters (2400 cubic yards), while the annual removal downstream of Highway 101 has been 190 cubic meters (250 cubic yards). So the average annual sediment removal needed for the watershed has been approximately 2000 cubic meters (2600 cubic yards). 7.1.2 Historic Infrastructure Maintenance As reported in Chapter 3, a detailed structural analysis of the concrete channel sections built in the 1960s revealed that much of the work conducted has deteriorated and significant lengths of the constructed channels are in danger of failure. As the facilities continue to deteriorate through various failure mechanisms, the danger of catastrophic channel failure (collapse of walls, possibly during a large flow event) becomes ever more possible. The District has been regularly monitoring the concrete channels over the past eight years, measuring wall deflections and assessing failure potential. A 65-meter (212 foot) length of the concrete channel between Mountain View Ave and Park Drive was judged to be close to collapse and was replaced in 2003, at a cost of approximately $640,000. Piecemeal replacement of channels combined with very difficult site access and limited right-of-way combine to create very expensive repair and replacement conditions. Permanente Creek Flood Protection Project Page 138 Planning Study Report July 2008 7.2 Continuing Project Maintenance Activities The Permanente Creek maintenance program provides long term maintenance guidance for routine and long term stream maintenance work. 7.2.1 Ongoing Sediment Maintenance It is anticipated that the existing level of sediment maintenance work, mostly concentrated in the Permanente Diversion and Permanente Creek just downstream of Highway 101 would continue into the foreseeable future. The flood detention project elements may reduce sediment generation from the very largest storms; however, since the target flowrates will typically be ten- year or above flows, there would be only minor reductions expected in average annual sediment removal needed. Thus, the conditions to trigger rriaintenance activity would be: Greater than 0.3 meter (1-foot) average sediment depth in the Permanente Diversion (above the invert grade shown on the projE~ct plans). Greater than 0.3 meter (1-foot) average sediment depth in Permanente Creek (above the invert grade shown on project plans) bc~tween Highway 101 and Charleston Road. Other improved channel reaches (Reaches; P2, P3, P4, P5, H1, P8, and the length of the Permanente Diversion) would continue to k~e monitored for sediment maintenance. These reaches are not anticipated to requi~•e regular maintenance; however, greater than 0.3 meter (1-foot) average sediment depth at these locations would be a maintenance activity trigger. If any of these conditions are met, the response would be maintenance to restore the channel to design condition at the earliest opportunity, gener~illy the following summer. 7.2.2 Ongoing Vegetation Maintenance The current level of vegetation maintenance would be continued in the future. Levees (annual cycle): continue to prevent vegetation growth along top of levee maintenance roads, prevent woody vegeta~lion establishment and growth on levee slopes or top. Concrete channel reaches (annual cycle): continue to maintain access areas and adjacent right-of-way clear of weeds and remove woody vegetation from within 1.5 meters (5 feet) of vertical walled concrete channels. Natural channel reaches (annual cycle): monitor within District right-of-way areas for hazardous tree conditions, channel blockages, etc. 7.2.3 Ongoing Structural Maintenance The concrete channel reaches experiencing the m~~st structural deterioration (portions of Reach P5 and the upstream end of Reach H1) would be replaced by new structures as part of the capital work. Thus, the most pressing portion of addressing the structural deterioration of the 1960s channels would be accomplished. Also, the lower part of Reach P3 (Highway 101 to Permanente Creek Flood Protection Project Page 139 Planning Study Report July 2008 Middlefield Road) would be replaced by a partially natural channel per the riparian restoration project element. The remaining concrete channels would be monitored annually by District maintenance. Wall deflections would be measured and compared with safety criteria at channel monitoring locations established by the District's structural engineering unit. The "impending failure" rate would be 0.175 (deflection from plumb /wall height). Therefore, any measurements close to this rating would be inspected more frequently. Ongoing deterioration close to the failure limit would trigger channel replacement. Levee elevations would be monitored once every five years and restored to design elevation if measured elevation varies from the elevation shown on project plans by more than 0.3 meters (1 foot). 7.3 Maintenance Activities for New Project Elements Maintenance activities for new project elements would be as follows. 7.3.1 Floodwalls In addition to typical levee maintenance (see above), new maintenance would include: • Visual inspection and monitoring: Floodwalls would be visually inspected on a monthly basis and graffiti control measures taken as needed. • Floodwall elevations would be monitored through surveying identified control points once every five years. If measured elevations vary from the as-built elevations by more than .15 m (6 inches), the foodwalls would be analyzed by a competent structural engineer for foundation problems. If measured elevations vary from as-built by more than 0.3 m (1 foot), then elevations would be restored to design elevation. 7.3.2 Riparian Restoration The reach would be visually inspected annually and the following work completed as needed: • Access road /public trail would be maintained free of weeds and other vegetation. • Safety rail would be inspected and repaired as needed. • Concrete channel bank would be inspected for visible scouring and wearing of concrete cover and repaired as needed. Graffiti would be controlled. • Invert, floodbench, and restored bank would be left as natural as possible with no required regular maintenance. Hazardous trees would be removed and replaced as needed. Bank failures would be identified as early as possible and repaired as needed. 7.3.3 New Concrete Channels The new channels along Reaches P5 and H1 would be maintained similarly to the current maintenance program. Annual inspections would be carried out to monitor for sedimentation, Permanente Creek Flood Protection Project Page 140 Planning Study Report July 2008 vegetation growth along maintenance access roui:es, and structural deterioration. The criteria detailed above for existing channels would be usE~d to determine maintenance activities needed. 7.3.4 New Bypass Culverts Bypass culverts would be designed with such gra~~e that sediment buildup would be unlikely. The inlet and outlet locations would be inspected annually for evidence of sedimentation. If any sedimentation within the culvert would be suspected, they would be inspected. Average sediment depths greater than 0.15 meters (6-inches) would trigger maintenance action to restore the culverts back to design condition. Inlets and outlets are far more likely locations for required maintenance activities over the long term: • Sediment tends to drop out just upstream ~~f inlet locations; therefore, these locations would be inspected annually. Sediment dE~pths greater than 0.3 meters (1 foot) above design conditions would trigger maintenance action to restore the grade back to design condition. • Bypass inlet locations would also be monitored for vegetation growth. Any woody vegetation or other impediment to clear flow into the inlet would be removed annually. • Both bypasses propose to outlet into controlled locations (Hale Bypass into a concrete channel and Permanente Bypass into a ro~:k-lined pool); therefore, it is unlikely there would be erosion issues at outlets. The PE~rmanente Bypass outlet would be monitored for vegetation growth. Any woody vegetation obstructing flows would be removed annually. 7.3.5 McKelvey Park Detention Area Day to day maintenance of park facilities including vegetation management would be conducted by the City of Mountain View. District maintenance responsibilities would lie in maintaining the inlet/outlet area adjacent to the creek and post-flo~~d cleanup of the site after a flooding event. The inlet/outlet and stilling basin locations would be maintained free of sediment and graffiti would be controlled. Access would be through thE~ baseball field, so maintenance activities would be conducted during times when park is not in formal use. The outlet pipe would be maintained free of blockage and vegetation. Post-flood maintenance would be conducted by a contractor. District maintenance would administer a contract with an appropriate landsca~-ing contractor who would be on call to clean and restore the field after any flooding event. Acti~rities would include removal of any deposited sediments from the site, restoration of any damag~~d items, restoration of damaged field areas (including the artificial turf, as needed), and repair of drainage facilities as needed. 7.3.6 Cuesta Park Annex Detention Area Day to day maintenance of park facilities, including vegetation management would be conducted by the City of Mountain View. District maintenance responsibilities would lie in maintaining the inleUoutlet area adjacent to the crE~ek and post-flood cleanup of the site after a flooding event. Permanente Creek Flood Protection Project Page 141 Planning Study Report July 2008 The inlet/outlet locations would be maintained free of sediment. Access would be through the park paths, so large equipment would not be used. The inlet and outlet pipes would be maintained free of blockage and vegetation. Post-flood maintenance would be limited to removal of deposited sediment from the site, restoration of any damaged items and bank failures, restoration of damaged vegetation, and repair of drainage facilities as needed. 7.3.7 Blach School Detention Area Day to day maintenance of school fields and facilities including vegetation management would be conducted by the school. District maintenance responsibilities would lie in maintaining the inlet/outlet area adjacent to the creek and post-flood cleanup of the site after a flooding event. The inlet/outlet and stilling basin locations would be maintained free of sediment and graffiti would be controlled. Access would be through District right of way. The outlet pipe and overflow weir area would be maintained free of blockage and vegetation. Post-flood maintenance would be conducted by a contractor. District maintenance would administer a contract with an appropriate landscaping contractor who would be on call to clean and restore the field after any flooding event. Activities would include removal of any deposited sediments from the site, restoration of any damaged items, restoration of damaged field areas (including the artificial turf and track, as needed), and repair of drainage facilities as needed. 7.3.8 Rancho San Antonio Detention Area Day to day maintenance of park facilities, including vegetation management and trail maintenance would be conducted by the County and the Open Space District. District maintenance responsibilities would lie in maintaining the inlet/outlet area adjacent to the creek and post-flood cleanup of the site after a flooding event. The inlet/outlet locations would be maintained free of sediment. The inlet culvert area may be prone to sediment deposition. This area would be inspected annually and restored to design grade once sediment deposition would exceed 0.3 meters (1 foot). The inlet location would also be maintained free of any woody vegetation growth. The outlet pipe would be maintained free of blockage and vegetation. Post-flood maintenance would be limited to repair of any bank failures, restoration of damaged vegetation, and repair of inlet/outlet facilities as needed. Sediment deposited in the detention area would be left in place. 7.3.9 New Diversion Structure The new diversion structure would likely require regular maintenance activity to perform as designed. Maintenance access would be provided to the vault area protecting the new diversion pipe as well as the main channel area (see Appendix H for engineering drawings). Both sides of the separation wall would be potential sediment deposition areas. Therefore, annual maintenance of this area would be required. Any sediment deposited would be removed. Permanente Creek Flood Protection Project Page 142 Planning Study Report July 2008 7.4 Long Term Infrastructure Maintenance Like all man-made structures, the new culverts, channel reaches, and other infrastructure that would be built by this project would eventually require replacement. Therefore, the calculated project maintenance costs (see below) include provisions for structural replacement costs estimated for the next 50 years, the project's desil~n lifespan. 7.5 Maintenance Cost Maintenance costs for the recommended alternative's project elements were calculated as follows: • Continuing sediment and vegetation m;~intenance: Based on a recent 10-year period, the annual cost of maintenance is ~~pproximately $120,000. This cost is not expected to change significantly due to thE~ project. • Rancho San Antonio detention: It is estimated that vegetation maintenance would be required at the inlet and outlet approximatE~ly once every 2-3 years, costing approximately $30,000. Annual costs would therefore be $10,000. • McKelvey Park detention: Significant maintenance would only be needed once every ten years, on average. However, the maintenance may include partial to full replacement of the artificial play surface. 1-he one-time cost is estimated at $150,000, with an annual cost of $15,000. There would also be typical maintenance of the inlet outlet area, graffiti control, etc. estimated a.t $5,000 annually. • Hale Bypass and Permanente Bypass: f~~r bypasses, a yearly maintenance $5,000 is estimated for inlet/outlet cleanup. Minimal regular maintenance would be needed for the culvert body; however, the structure would deteriorate with time, incurring replacement costs for the District. It is assume that 25 percent of the culvert length would fail over the first 100 years of project life. Thus, to fairl~r estimate the real long term costs of structural solutions, a structural replacement cost was added to the maintenance cost. For Hale Bypass this cost would be $22,7F~0 annually; while for the Permanente bypass it would be $11,500 annually. Floodwalls: There would be a $10,000 an~~ual cost for graffiti and weed control. The structural replacement cost would assume that 50 percent of the floodwall would need to be replaced in 100 years. Therefore, the annual cost for structural replacement would be $22,500. Channel widening. Annual sediment/vege~tation maintenance would be zero (included in the continuing maintenance costs above). However, the structural replacement cost for open channels would assume that 50 percent of the channel will fail over 100 years (based on previous District jobs). Therefore, the annual structural replacement cost would be $66,500. Riparian Restoration: Annual vegetation rind bank repair cost is estimated at $20,000. Permanente Creek Flood Protection Project Page 143 Planning Study Report July 2008 • New Diversion Structure: The annual sediment maintenance cost is estimated at $10,000. The structural replacement cost assumes 25 percent replacement every 100 years or $1,500 per year. • Cuesfa Annex Flood Detention: Annual maintenance for inlet/outlet area clearing is estimated at $5,000. Post-flood cleanup is estimated at $150,000 per event, with a 2 percent annual event probability giving an annual cost of $3,000. • Blach School Flood Detention: Annual maintenance for inlet/outlet area clearing is estimated at $5,000. Post-flood cleanup is estimated at $150,000 per event, with a 10 percent annual event probability giving an annual cost of $15,000. • Structural Replacement Cost. As described in Section 6.2, the most deteriorated portions of the 1960s concrete channels will be replaced as part of this project. However, significant lengths of the concrete channels will remain and will continue to deteriorate with time, eventually requiring replacement. It is estimated that 25 percent of the remaining (not rebuilt) concrete channels (totaling 1600 feet) will fail over the next 50 years. Since these would be replaced as emergency projects, the costs are significantly greater than a planned construction project. Based on the 2003 channel replacement, the cost is estimated at $3000 per foot of channel. Therefore, the annual cost would be $96,000. In summary, the annual sediment and vegetation maintenance costs for the project would be approximately $228,000. The annual structural replacement costs would be approximately $211,000. The total annual cost would be $439,000 with a 50-year cost of approximately $22 million. Please see Appendix E for details of maintenance cost estimates. Permanente Creek Flood Protection Project Page 144 Planning Study Report July 2008 CHAPTER 8 PROJECT COST, FUNDING, AND SCHEDULE 8.1 Project Cost The overall capital cost for the recommended project would be $58 million in 2008 dollars, including design, construction, and contingencies. Of that, $40 million would be needed to meet the project`s CSC commitments. Since the project's budget is limited, it is recommended that only the project elements needed to meet CSC commitments be designed and built at this time, saving the remainder of the project elements for future design/construction efforts. The capital design/construction estimate is summ,~rized below in Table 8.1. The detailed cost estimate is provided in Appendix E. The project elements in normal font would be the ones recommended for current phase design and conslruction, while the elements in italics font are for potential future design and construction phases. Table 8.1 -Summary of De:~ign/Construction Costs Project Element Design/Construction Cost millions 2008 $ Flow detention - Rancho San Antonio $5.5 Flow detention - McKelve Park $9.1 Hale B ass $10.2 Permanente B ass $5.2 Floodwalls $2.8 Channel widenin Reach P5 $5.2 Channel widenin Reach H1 $1.6 Channel widenin Reach H1 $8.2 New diversion structure $0.7 Flow detention - Cuesta Park Annex $3.6 Flow detention - Blach School $6.3 8.1.1 Potential Enhancement Opportunity It would be possible to restore riparian values and extend public trails along approximately 700 meters (2300 feet) of current concrete-lined channel between Highway 101 and Middlefield Road. Doing this would also permanently addres:c the deteriorating concrete channels along this reach of Permanente Creek. This project element would cost an additional $3.5 million. Another potential enhancement opportunity would be restoration of the Permanente Diversion Channel to a riparian habitat connecting the natur~~l upper portions of Permanente Creek with Stevens Creek. This would also provide an opportunity to extend a public trail from the Stevens Creek area to upper Permanente Creek. This would also address the deteriorating concrete channels along the Permanente Diversion channel. The cost for doing this restoration would be quite substantial, though grant funding from various State of California initiatives may partially offset some of the costs. Permanente Creek Flood Protection Project Page 145 Planning Study Report July 2008 8.2 Project Funding The design and construction phases of the Permanente Creek project would be paid by funds from the voter approved CSC Measure B ballot measure. Funds from the Measure have begun accumulating in the project's budget and would be used through the design and construction phases. The expected total budget available to this project by the end of the Measure's existence in 2016 is approximately $38.6 million. 8.3 Project Schedule Detailed project design is expected to begin in the second half of 2008. The overall project will be split into three design/construction phases, based on the type of work and the anticipated complexity of the design effort. These phases will be as follows: 8.3.1 Phase 1 This phase will include mostly concrete channel improvements. The design and plans would be done by District staff. Project elements included are the new diversion structure, floodwalls, and the channel improvements in Reaches P5 and H1. Design and plans and specifications preparation would be conducted from January 2009 to June 2010. Construction, including revegetation would be conducted from January 2011 through June 2012. 8.3.2 Phase 2 This phase would concentrate on the Rancho San Antonio flood detention project element. Since this area is to remain in natural condition, the design and plans work could be done by District staff and do not require specialized parks design expertise. Design and plans and specifications preparation would be conducted from January 2009 to December 2010. Construction, including revegetation would be conducted from June 2011 through April 2012. 8.3.3 Phase 3 This phase would be composed of the other three flood detention sites, which generally require a level of landscaping and park design expertise not readily available at the District and the Permanente Bypass culvert, which would connect the Cuesta Park Annex site with the Blach School site. This work would be expected to take a somewhat longer design time. The project elements included would be Blach School detention, McKelvey Park detention, Cuesta Park Annex detention, and the Permanente Bypass. Design and plans and specifications preparation would be conducted from January 2009 to July 2011. Construction, including revegetation would be conducted from February 2012 through 2015. Permanente Creek Flood Protection Project Page 146 Planning Study Report July 2008 CHAPTER 9 CONCLUSIONS AND Fi~ECOMMENDATIONS The existing flow carrying capacities of Permanente Creek, Hale Creek, and Permanente Diversion are far below the design flow rate. If the flood protection is not improved, 3,170 parcels located in Mountain View and Los /~Itos would be flooded by aone-percent flow event. The recommended project would provide protecti~~n to the community from the design flood and accomplish the District's CSC natural flood protection objectives. The following would be the beneficial impacts of the project: • Flood protection: The full project would protect all 3,170 parcels subject to one- percent flooding in the watershed. The CSC phase design and construction recommended would protect 2,470 parcel:, including all of the approximately 1,670 parcels in the floodplain north of EI Camino Real. • Flood protection: The project would prol:ect Highway 101, Central Expressway, and Middlefield Road from flooding due to the one-percent event. • Environmental enhancement/trails: Tlie project would provide an opportunity for riparian restoration and trail extension for ;approximately 700 meters (2300 feet) of existing concrete channels. • Concrete channel deterioration /asset protection: The project would replace the most significantly damaged sections of thE~ old concrete channels and provide a monitoring/replacement plan for long term maintenance. • Maintenance: While the annual sediment: and vegetation maintenance is not expected to change from existing practice, the project would address the structural deterioration maintenance concern. The project meets all the specific project objectivE~s and balances the NFP objectives adopted by the District Board better than all other feasible alternatives. Therefore, it is recommended that the project should be approved and that detailed plans and specifications be developed for its construction. Permanente Creek Flood Protection Project Page 147 Planning Study Report July 2008 All Appendices & Plan Sheet Available Upon Request Contact Saeid Hosseini, Sr. Project Manager x2680