San Leandro Marina Alts Study_Final

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5. Alternatives for Future Use of the DMMS Seasonal wetland restoration These alternatives, along with the No Action alternative are described below. 5.1 Existing Conditions Land Use. The DMMS is a 112 acre former baylands (salt marsh) site bordered by the Estudillo Channel to the north, by the recently restored San Leandro Shoreline Marshlands (SLSM, also known as the Robert Landing area) to the south and southeast, by residential development to the east, and by the Monarch Bay Golf Course to the west (see Figure 1-1). Perimeter levees surround the DMMS and a cross levee separates the site into two basins — the West Basin and East Basin. Since 1973, the site has been used for temporary drying and storage for sediment dredged from the federal Channel and Harbor Basin. Material from maintenance dredging is deposited in the DMMS, where it is dried and later trucked offsite. Upon removal of the material, the site is graded to slope gently from +3 ft NGVD at the south end to +1 ft at the north end, with several bird habitat islands graded to +4 ft (Attachment F).15 The site is disced periodically to prevent significant vegetation from establishing. Approximately 90,000 cubic yards of dredged material were placed on the DMMS in late 2009, 33,000 CY in the west basin and 57,000 CY in the western half of the east basin. No material removal or grading has occurred since this time (D. Pollart, pers. comm.). Hydrology. Tidal waters flow into the site from the SLSM, through tide gates, and discharge through six decant weirs to Estudillo Canal. The site also ponds direct rainfall. Tidal inflow to the site is limited to the highest tides during the winter and spring, when Bay waters are elevated due to "spring" high tides and high freshwater runoff (T. Roberts, pers. comm.). The SLSM marshes to the south of the DMMS are muted tidal, with culverts limiting tidal exchange. Estudillo Canal immediately north of the DMMS is also not fully tidal. A tidegate structure across the mouth of Estudillo Canal keeps bay water from entering the canal during high tides (ACFCWCD 2007). The canal is managed for flood protection by Alameda County Flood Control and Conservation District. No water level monitoring data were available for the site and adjacent areas (SLSM and Estudillo Canal) for this study. Biology. The site is required by RWQCB permit (1990) to maximize wetland habitat values for shorebird usage between dredging events. Little or no biological monitoring data exists for the site. Based on anecdotal observations during monitoring of the adjacent SLSM marshes, the site provides habitat for migratory and wintering shorebirds, though habitat quality is likely low. Periodic disturbance of the site for dredged material placement limits development of the invertebrate community and therefore limits the quality of shorebird foraging. 15 Elevations in the 2004 grading plan are referenced to "NGVD (1973 adjustment)," treated as equal to NGVD29 for this study. All elevations in this memo are referenced to the NGVD29 datum. San Leandro Marina Harbor Basin 5-2 ESA / 210461 Alternatives Study March 2011