1/30/20061

San Francisquito Creek Flood Control

January 30, 2006

Crescent Park Neighborhood Association

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Outline

Situation todayBackground of SF CreekCreek simulation methodology and findingsProposed solution to protect against a 1998-level floodHow does this fit with the GI project?Legal IssuesRecommendations and next steps

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Situation Today ...

New Year’s Eve near-flood event renewed community concerns, especially about the Chaucer Street BridgeThe Army Corps of Engineers (ACoE) General Investigation project has a long timeframe (20 to 40 years) and is fraught with uncertaintyContinuing threat to property and public safetySignificant liability for the City of Palo Alto due to Chaucer Street BridgeLocal leadership and involvement necessary

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Background of SF Creek

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Flooding in 1998 - 7200cfs

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Problems from man-made structures

Creek rerouting – City of PA ~1928(east of 101)

Bayshore/101 bridge – State of CA ~1960

Chaucer/Pope bridge – City of PA 1948

Middlefield bridge – City of PA 1932

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Chaucer/Pope in 1907

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Chaucer/Pope rebuilt in 1948

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Chaucer St. Bridge as designed in 1946. Original height on centerline (invert to soffit) = 19.5 ft; current height ≈ 16.5 ft

Chaucer/Pope before & after

Filled with earth

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Simulation methodology

Stephen G. Monismith

ProfessorEnvironmental Fluid Mechanics

Director, Environmental Fluid Mechanics

Laboratory

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Simulation methodology

Model-based analysis enables system-wide approach» Identify where creek fails under increasing flow rates» Hypothesize fixes and test them for effectiveness

Corps of Engineers HEC-RAS 3.1 hydraulic analysis code – current standard for analysisLatest creek survey data by SCVWD, updated for 2002 levee/floodwall projectModel calibrated to 1955, 1982, and 2002 events –also correlated with 1998 and Dec 31, 2005 observational data

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5000 cfs Flow Water Surface

Bayshore

NewellUniversity

Chaucer

Middlefield

El Camino

Bridge Problems

Bank Problems

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7200 cfs Flow Water Surface

Bayshore

NewellUniversity

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Middlefield

El Camino

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Bank Problems

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7200 cfs Flow Water SurfaceNo Chaucer Street Bridge

Bank Problems

Bayshore

NewellUniversity

Chaucer

Middlefield

El Camino

Bridge Problems

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Wall Heights (+3ft) for 7200cfs

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6000 cfs Flow WS –No Chaucer Street Bridge

Bank Problems

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NewellUniversity

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Middlefield

El Camino

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Proposed 7200cfs Solution

Raise banks downstream of 101 to hold 7200cfsWork with Cal Trans to add fourth tube to 101 bridgeRaise banks between 101 and Chaucer to hold 7200cfsCity of Palo Alto replaces Chaucer bridge» Cost $3.0 to 3.5M» Palo Alto receives in-kind credit against future GI

matching costs

Note: Protection for flows over 7200cfs to be accomplished by the GI

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Advantages to

City of Palo Alto … significantly reduced liabilities and no increase in overall GI costsHomeowners in all three cities … near-term protection from 1998-level floods and eventual protection from 100-year and tidal floodingJPA and ACoE ….Full political support for the GI and an increased probability of passing the needed bond issues. The JPA will have demonstrated its competence, and the voters are much more likely to approve the bond issue.

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How does the Short-term Solution fit with the GI?

Won’t significantly reduce GI cost/benefit» 100-year flood damage estimated at $780M

(ACoE 905b)» Reducing by $50-60M won’t change benefits

very much» Tidal flooding still has to be handled

Replacement of the Chaucer Street bridge and upgrade of the 101 bridge will certainly be part of any GI proposed solution.

Why not do it ASAP?

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Legal issues

Suit for damages in 1998 settled for $3.5M

City of Palo Alto is liable for damages under the principle of “inverse condemnation”

Palo Alto would not be liable for downstream flooding resulting from replacement of the Chaucer Street bridge based on California Supreme Court Decision - Locklin v City of Lafayette.

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Responsibility

The City of Palo Alto has the primeresponsibility to protect its own citizens from harm caused by water diverted from the natural stream course.

The City of Palo Alto also has the responsibility to support and assist the neighboring communities in protecting themselves from harm caused by fluvial and tidal flooding.

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Recommendations and Next Steps

The JPA and its individual members ( Particularly the Palo Alto City Council) need to quickly agree that a short-term solution is necessary.The Santa Clara Water District engineers should update the HECRAS calculations or the JPA should hire a consulting firm to do so. Waiting for the ACoE just takes too long and the JPA needs to demonstrate to the future bond voters that it is an effective organization.

Move ahead on the short-term solution!