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Napa River-Napa Creek Flood Protection Project

The Project extends through the city of Napa from Highway 29 at the Butler Bridge on the south to Trancas Street on the north, encompassing six miles of the Napa River and one mile of Napa Creek.

The Project is designed to protect the community from flooding up to the level of the 100-year event. The 100-year event is a flood that has a 1-in-100 chance of occurring in any given year. While the average annual flow of the Napa River is about 1,300 cubic feet per second (cfs), the 100-year flood event produces an estimated flow between 41,000 and 46,000 cfs. That equals about 20 million gallons of water per minute passing through the heart of Napa. The devastating Napa flood of 1986 was classified in the Project’s General Design Memorandum as a 35-year flood.

The “Living River” design has been described as a new paradigm for flood protection projects in the United States. “Living River” principles include reconnecting the river to its historic flood plain; maintaining the natural slope and width of the river; allowing the river to meander as much as possible; retaining natural channel features like mud flats, shallows and sandbars; and supporting a continuous fish migration and riparian corridor along the river. To achieve these objectives, old dikes have been breached to restore tidal marshlands; bridges are being replaced to remove obstacles to water flow; riverbank terracing is creating more room for large volumes of water; a dry bypass channel will provide a shortcut for the river during high flood flows while sustaining the natural Oxbow habitat; new dikes, levees and floodwalls will be built; bank stabilization will be used in specific areas; and detention basins and pump stations will accommodate runoff behind the floodwalls.