Nov 02, 2015

Oro Loma, Castro Valley Sanitary Districts Complete Horizontal Levee

Project tests alternative to sea rise protection along San Francisco Bay shoreline

vegetation, levee, erosion control

On Thursday, April 9, construction started on a shoreline experiment that may help the Bay Area adapt to projected sea rise and extreme weather. Construction of the experimental levee is now complete, and Save the Bay initiated planting efforts on Nov. 1, 2015.

The Oro Loma horizontal levee project includes a wetland basin and a new type of levee known as a "horizontal levee." This wide, gently sloping wedge of gravel, mud and grasses mimics a historic wetland ecosystem that existed before settlement in the Bay Area.

Treated effluent from the Oro Loma facility will flow into the basin, be piped to the top of the horizontal levee, and flow through the soil to sustain native plants. This vegetation will provide wildlife habitat and remove nutrients that threaten water quality.

Most significantly, engineers see the horizontal levee as a natural buffer that can absorb storm surges and provide natural protection from flooding at a fraction of the cost of traditional levees. If successful, the approach could reduce the cost of typical flood response by half.

"If you can create a really wide rough levee, [covered with plants], it will slow waves down, and maybe you can actually build a smaller levee. Also, what we're building in these cases is not technically a levee, but a sloping terrace, or ramp, against a levee," said Peter Baye, coastal ecologist.

Phase I of the project is now completed, and community volunteers mobilized by the regional environmental nonprofit group Save the Bay will plant more than 70,000 native plants in Nov./Dec. 2015.

Researchers at the University of California, Berkeley will lead the monitoring effort to quantify the effectiveness of the levee. The experient will provide a much-needed field test of how treated wastewater and these new kinds of levees can help address critical flood protection, water quality and wildlife habitat issues.

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