Alviso Slough Restoration Project



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Alviso Slough Restoration Project
Alviso Slough is the last reach of the Guadalupe River before it enters San Francisco Bay. The community of Alviso is located on the east bank of the Slough. The Alviso Marina County Park, Don Edwards San Francisco Bay National Wildlife Refuge, and Cargill salt ponds occupy most of the area in Alviso that is outside the Urban Service Area. Coyote Creek, which drains a very large watershed, enters the Bay to the north of Alviso.

The town of Alviso has experienced a gradual sinking of the shoreline due to land subsidence caused by over pumping of groundwater in the first half of the 20 th century. This has required the construction of higher levees to protect the town from flooding during large storms as it did during the flood of 1983. Cargill’s ongoing maintenance of non-engineered salt pond levees to protect its industrial interests has also benefited Alviso. The levees have provided a physical barrier to tidal flooding thus far. However the South Bay Salt Pond Restoration effort will eliminate some of the levees, thereby increasing tidal flood risk to the town.

The District is currently constructing the Lower Guadalupe River Flood Protection Project (LGRP). Channel modifications for the project are being implemented from Interstate 880 (I-880) to the UPRR bridge. The LGRP planning phase also included a reconnaissance level investigation of the Alviso Baylands (roughly the area from the UPRR bridge downstream to the Bay). The Alviso Baylands Study, completed in 2002, confirmed that the area is subject to flooding from several sources other than the lower Guadalupe River, including the lower section of Coyote Creek, Guadalupe Slough, and the tidal/storm surges in South San Francisco Bay.

Project goals:

Remove seven acres of vegetation and root mass to a depth of four feet between the Gold Street Bridge and County Marina.
Restore the slough’s open water channel width to prior to 1983 conditions. Photos of the slough from 1982 are shown in Attachments 2 and 3.
Improve navigation so the community can expand on boating and other recreational opportunities.
Restore historic public access and aesthetics for the Alviso community.
Maintain one-percent flood protection in Alviso Slough.
Reduce mosquito nuisance.
Expand open water habitat and inundated mudflat habitat of the slough.
Promote the integration of the salt water connections that should result from the South Bay Salt Pond Restoration Project with this project.