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5. Alternatives for Future Use of the DMMS <br />To maintain a reduced size marina under the Marina Park alternative requires dredging approximately <br />105,000 CY (Channel only) to 115,000 CY (Channel and Marina) every four years. Based on the <br />rough numbers prepared for this study, the shorebird habitat DMMS alternative may be able to <br />accept material from 50-60% of one dredge event and the tidal marsh DMMS alternative may be <br />able to accept material from 75-85% of one dredge event. The ranges reflect with and without <br />Marina dredging. These numbers assume maximum fill placement, which would need to be <br />confirmed based on existing ground elevations and tides. The seasonal wetland alternative could <br />accept material from roughly two dredge events. <br />Landscape Change with Sea Level Rise <br />Sea level rise is expected to change the future economic and physical landscape in the site vicinity. <br />Though the exact rate of sea level rise is not known, it is generally anticipated to be 10 to 17 <br />inches by 2050. As sea levels rise, there will be increased risk of overtopping of the existing <br />outboard (bay) levee. Investment will be required to maintain the existing outboard levee or to <br />retreat to a new inboard levee. <br />Operating the site as a DMMS for other harbors could become more valuable with future sea level <br />rise, as fill is increasingly needed for new levee creation and for raising low-lying areas around <br />the margin of the bay. Operating the DMMS would require ongoing O&M to protect site uses <br />with sea level rise. <br />The tidal marsh and seasonal wetland habitat types would be resilient to sea level rise and set -back <br />of the protected shoreline. Tidal marsh sedimentation would build the marsh surface vertically as <br />sea level rose. Seasonal wetland would gradually convert to high intertidal marsh habitat and, because <br />it is high in elevation, provide good shoreline protection in the form of absorbing wave energy. <br />While the shorebird habitat alternative would become increasingly difficult to manage to meet <br />habitat goals, preservation of this type of habitat could take on additional importance as mudflat <br />habitat around the bay decreases. <br />San Leandro Marina Harbor Basin 5-7 ESA / 210461 <br />Alternatives Study March 2011 <br />