Bay Levee Armoring

This project was a tidal wetland enhancement that involved multiple agencies including US Fish and Wildlife, Valley Water, San Francisco Bay Bird Observatory, and Santa Clara County Parks.

Along the edges of San Francisco Bay, tidal marshes provide refuge for sensitive and endangered species during high tides. These species include the American Avocet, Black-necked Stilt, California Clapper Rail, Salt Marsh Harvest Mouse, Snowy Plover, and the Western Sandpiper. The marshes also perform as a flood control zone for the South Bay watershed. The area situated between the lower marsh plains and higher elevation is the upland transition zone.

Tidal salt marshes are vital for a healthy Bay. They are biologically productive ecosystems. The cyclic flow of tides continually injects fresh sea water containing food and oxygen, into the ecosystem while it flushes out waste products. Shallow marsh waters also produce vast amounts of macroscopic nourishment for wildlife and enrich the muddy soils through the breakdown of dead organisms.

The engineers on this project needed an alternative to 24" rip rap for levee protection on the water side of the levee. Rip rap is not readily available in the Bay Area, but more importantly, US Fish and Wildlife goal was to restore the upland transition zone by planting native perennials such as California Buckwheat, Salt Grass, Cordgrass, and Pickleweed while also removing invasive plants.

The design team specified Tied Concrete Block Mat, Flexamat® UV-T-10-NW. This concrete mat had a non-woven geotextile as underlayment to protect the shoreline from wave attack immediately upon installation.

Each truckload of Flexamat® concrete mats saved 32 dump trucks from hauling rip rap through the Bay Area, a massive cost savings and reduction in the carbon footprint. Overall, the use of Flexamat® cut installation time by over 60% in comparison to 24" rock rip rap.