San Leandro Marina Alts Study_Final

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5. Alternatives for Future Use of the DMMS with an approximate high tide range of 2.7 to 4.0 ft over the spring -neap cycle. High water levels at the SLSM intake are an unknown amount lower than Bay tides. Existing culverts and weirs would be supplemented or replaced with additional hydraulic structures to allow greater flows and management flexibility. O&M would consist primarily of water management, vegetation management (less than current level of vegetation management), and periodic levee maintenance and replacement of hydraulic structures. Implementation of the Shorebird Habitat Enhancement would require up -front funding for construction and ongoing funding for O&M. This alternative would have a relatively high cost and would most likely be pursued only in partnership with a public or private entity, such as the California Department of Fish and Game, who could help bring grant funding for construction and assume responsibility for ongoing management. Tidal Marsh Restoration The tidal marsh restoration alternative would create a predominantly pickleweed marshplain with channels and small areas of upland refugia. The extent of channels would depend on habitat objectives and funding availability. The DMMS would function similarly to the adjacent SLSM marshes, which provide suitable habitat for salt marsh harvest mouse (SMHM) and California clapper rail (CCR). The site would be raised using up to 90,000 CY of dredged material to create the marshplain. The 90,000 CY fill volume assumes the site is filled to 2.7 ft. The design elevation and amount of fill would depend on tide levels at the adjacent SLSM marshes and Estudillo Channel. Channels would be excavated (or avoided during material placement) to provide drainage to and from the marshplain. Additional channels (more than the minimum required for drainage) would provide additional channel habitat for the CCR, as well as improved drainage, and would be constructed if funds permit. The existing weirs and culverts at the site would be removed or abandoned in place. O&M costs would be minimal, consisting primarily of vegetation management (much less intensive than current levels of vegetation management). Seasonal Wetland Restoration The seasonal wetland alternative would fill the site above tidal elevations to create fresh to brackish seasonally-ponded areas. The site would pond direct rainfall during the winter and spring and be dry during the summer and fall. The site would be raised using approximately 210,000 CY or more of dredged material. Limited monitoring of seasonal wetlands created on dredged material around San Francisco Bay indicates that these areas provide shallow open water habitat used by shorebirds initially, then — in the absence of vegetation management or an ongoing source of saline bay water — vegetate with upland native and invasive plants over several years to a decade (e.g., seasonal wetlands at Bair Island in San Mateo County and Corte Madera Ecological Reserve in Marin County). O&M San Leandro Marina Harbor Basin 5-5 ESA / 210461 Alternatives Study March 2011