14. Scenic Circle Bridge
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OUNCIL ACTION
Authorize removal of the Scenic
Circle bridge as part of the Stevens
Creek Corridor Restoration Project
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Currently, the
bridge is in place
but access to it
been blocked
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BALANCE HYDROLOGICS, Inc.
Memo
To: Therese Ambrosi Smith
From: Shawn Chartrand
Date: Tuesday, July 17,2007
Subject: Response to Questions Regarding the Scenic Circle Bridge, Stevens Creek
As requested, we have provided feedback below regarding replacement or no action to the Scenic
Circle Bridge, Stevens Creek, Blackberry Farm, Cupertino.
1. What are the major problems if City does not remove the bridge & abutments?
Leaving the bridge and abutments in place could pose a significant risk to the design reach and
the new downstream bridsze if it were to fail during a storm. Obviously, severe damage could
occur in that scenario. Beyond that concern, the design reaches have been designed such that the
bridge itself should not cause problems for the other reaches as long as it does not fail in any
way. It should also be noted and brought to Council's attention that the existing bridge was a
temporary replacement for one that already failed, so betting that it will not fail is a highly
unlikely proposition. It is only a matter of time till we get a big storm/EI Nino year again.
2. Does removal of the bridge/abutments require substantial redesign of other areas of the
channel? How much? Entire length or just a stretch upstream?
Removal of the bridge does not likely require substantial re-design of the design reaches
immediately upstream of downstream of the bridge. It is likely that the bridge site could be
designed as it's own element where we would tie into existing channel features and also build in
some grade control protection. One could easily make the argument that the bridge reach should
be connected to both the horseshoe bend reach and the low-flow crossing site as it would only
involve 75 feet of additional channel to build in either direction beyond what I have indicated in
the attached pdf document. Given this argument, the existing design for the two reaches
upstream and downstream of the bridge reach would need some minor tweaking but nothing
likely substantial. Ballpark for the design and minor re-design would be $4,000-$7,000. This
does not include evaluation of any utilities which would need to be dealt with - it WOULD
include design of the channel banks, grade control structures, and channel bed structures.
3. Does removal require hydraulic recalculation? How extensive?
It is likely -reasonable to assume that the hydraulic model would need to be re-run with a new
design given that the bridge in and of itself represents a somewhat significant local flood flow
obstruction. I would guess that floodwater elevations up to perhaps the 10-year event might
lower locally to the bridge with it gone. I would estimate a several thousand dollar cost (3,000)
to refining the existing hydraulic model.
4. What are the expected timeline impacts of the removal & assoc. redesign?
Unlikely that the additional design would slow things down on our end but perhaps it would for
the group process.
5 . Would any new problems be created?
After the channel design changes are drafted, it will be necessary to revisit the tree removal and
vegetation plans to insure that we are acting in accordance with the approved CEQA document.