FLOOD08871

• County: Statewide
• Basin: Statewide
• Title: Mitigation Success Stories in the United States
• Date: 1/1/2002
• Prepared By: FEMA
• Floodplain - Doc Type: Flood Mitigation/Flood Warning/Watershed Restoration

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Location: Napa County, California
Project: Flood Protection and Watershed
Improvement Project
Techniques: Living River Strategy, Public/Private
Partnership, Multi-Agency Coordination,
Non-structural Channel Modification,
Redesign of Bridges, Dikes and Levees
Contact: Clark Frentzen, U.S. Army Corps of
Engineers, South Pacific Division,
[e-mail] or 415-977-8164

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Napa Coun

Background
Napa City and Napa County have a history of periodic flooding from the
Napa River :Uld Napa Creek. At one time, the Napa River supported a
dense riparian forest, prO\ided significant wetland habitat and induded productive spa"'11ing areas for fish, such as salmon and steelllead.
P,.essures from urbmtization, agriculture and grazing have degraded these habitats and the quality of the Napa River's natural emironment.
The existing natur.d drJinage system provided by the Napa River and Napa Creek is not adeqnate to prevent extensive flooding mId asso-
ciated property damage. In the past 36 years, Napa County residents have sustained $542 million in property damage :done. The City of
Napa has experienced 27 major floods during a 135 year period, from 1862 to 1997; on the average this is a major flood every five years!

PrOject Description
The Napa County Flood Protection and Watershed Improvement Project will provide flood protection by reconnecting the Napa River to
its floodpl:tin, creating wetlands throughoUlthe area, maintaining fish habi~~t, m:untaining \Vildlife habitat, and ret:tining the natural char-
acteristics of the River. Residents, businesses, local government, State government, environmental groups, wineries, the Chamber of
Commerce and the USACE formed a coalition and agreed to the follo"'ing goals:

. Achieve ., 1 % chance flood." protection.
. Restore the living environment of the Napa River.
. Enhance the opportunity for econonuc development.
. Develop a local fimUlcing plan that the conunnnity can support.
. Develop a plan that addresses tile entire watershed, county-wide.

Several specific project features will help to achieve these goals:

. I.owering or removing the dike south of Imola Avenue to allow the Napa River to flow in a wider area, thereby increasing conveY:Ulce
capacity and reducing upstremn water surface elevations.
. Modifying the channel to create flood terraces, which \ViII create addition:t1 storage capacity along the River and lower water surface
elevations, contributing to approximately 500 acres of created wetland anti upland habitat.
. Develop a '.dry" bypa." channel to bridge tile Oxbow. Tbis bypa." ",ill allow low water flows to remain in the Oxhow, and help m:tin-
tain natural characteristics. During flood flows, water ",ill be diverted out of the Oxbow and onto a more direct route tbrough
central Napa.
. Construct new dikes, levees and floodwalls to contain the "1% chance flood'" event. Three pump stations vvill remove water from
behind floodwalls and levees and pump water into the Napa River.
. Remove and replace a number of bridges in dO\Vl1l0wn Napa City. The repiacement bridges will be designed with higher deanmces
to beller pa." flood flows.
. Reduce dredging and return tidal inflnence to historic baylands.

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Benefits
. Increa.,e in conveyance capacity and reduction of upstream water surface elevations.
. Creation of additional storage capacity aloog the River and lower water surface elevations.
. I.ow water flows will remain in the Oxbow and help maintain natuntl characteristics. Hood water ",ill he diverted out of tile Oxbow and
onto a more direct route through central Napa.
. Replacement bridges will beller pass flood flows.
. Tidal inIluence \Vill be returned to historic haylands.
. Realization of $26 million, annually, in avoided property d:unage, reduced insurance costs, avoided de:m-up, avoided costs of emer-
genc)' services and enhmlced environmental improvemenK

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