Laserfiche WebLink
5. Alternatives for Future Use of the DMMS <br />5.2 Assumptions <br />Muted tidal (not fully tidal) flows are available to the site. Estudillo Channel is not fully <br />tidal and must remain managed with flap -gated culverts for flood protection. The SLSM <br />marshes are muted tidal. <br />No topographic information is available for the DMMS. For the purposes of this study, we <br />assume DMMS grades prior to the 2009 material placement were as shown in Attachment F <br />and that approximately 0.6 ft were placed in all but the highest areas of the west basin <br />(33,000 CY over nearly 40% of the site), resulting in a gentle slope from +3 to +1.6 ft and <br />that 1.5 ft were placed in all but the highest areas of the western half of the east basin <br />(57,000 CY over nearly 30% of the site), resulting in a gentle slope from +3 to +2.5 ft. <br />These estimates are approximate, for planning purposes only. <br />• Sediment quality in the DMMS is suitable for establishing wetland habitat. <br />• Invasive Spartina alterniflora and its hybrids will need to be controlled/eradicated <br />regionally prior to any restoration of the DMMS. <br />• Perimeter levees of the DMMS are sufficiently high for placement of fill material to design <br />grades, or can be raised if needed. <br />• Flood management requirements for Estudillo Channel do not impose DMMS grading or <br />land use constraints. <br />These assumptions should be confirmed and revised as necessary, during later alternative refinement. <br />5.3 Alternative Descriptions <br />The DMMS alternatives are described below. Table 5-1 summarizes fill volume and relative cost <br />by alternative. <br />TABLE 5-1 <br />COMPARISON OF DMMS ALTERNATIVES <br />DMMS Alternative <br />Potential Fill Volume <br />(Approx.) <br />Construction Cost <br />O&M Cost <br />No action <br />0 CY <br />None <br />Low <br />Operate as DMMS for other harbors <br />Current: 0 CY <br />None <br />Low -moderate <br />Future: potentially high <br />Shorebird habitat <br />0 to 60,000 CY <br />High <br />High <br />Tidal marsh <br />0 to 90,000 CY <br />Moderate <br />Low <br />Seasonal wetland <br />210,000 CY <br />Moderate <br />High <br />No Action <br />In the absence of a Harbor Basin project, use of the DMMS for dredged material handling would be <br />discontinued. Inflow and outflow infrastructure would gradually deteriorate, likely leading to <br />somewhat increased frequency of inundation of the site. In the absence of ongoing operations <br />San Leandro Marina Harbor Basin 5-3 ESA / 210461 <br />Alternatives Study March 2011 <br />