San Leandro Marina Alts Study_Final

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4. Alternatives Nature Park Alternative After the initial work to create high marsh or island areas no on-going maintenance dredging would occur under this option. Dredge Materials Disposal Concept The Dredge Materials Disposal Concept is described and illustrated in detail in Section 3. Required dredging for the concept was evaluated assuming the current maintenance depth and a reduced maintenance depth. The usual practice is to dredge the federal Channel to -7 feetl1 MLLW while the berthing area within the Marina is dredged to -7 feet MLLW (both include 1 foot of over -dredge). This maintenance activity has historically been completed on a 4 -year schedule for the Channel and an 8 -year schedule for the Marina berthing area12. The reduced maintenance scenario would be to dredge the Channel and the Marina berthing area to -5 feet MLLW (+1 foot overdredge) and reduce the approach Channel from the present width of 200 to 120 feet. For comparison purposes, the same dredge cycles are assumed for the reduced depth scenario. The volume of dredge material for 4 -year and 8 -year dredge cycles is presented in Table 4-2 for current and reduced maintenance depths. TABLE 4-2 DREDGE VOLUME COMPARISONS 4 -year 8 -year Historic 160,000 CY 180,000 CY Reduced 105,000 CY 115,000 CY (Proposed Concept) These values assume that only half of the Marina basin, which includes a portion of the federal Channel and the Marina berthing area, would be dredged. By reducing the depth that would need to be maintained, the volume of material dredged would reduce by approximately 27%. As stated in Section 3, the dredge material could be used to create high marsh refugia in the South Basin and western portion of the Harbor Basin. The assumed area, depths, heights, consolidation, and volume for each refugia is presented in Table 4-3. Assuming that the Channel is dredged on a 4 -year cycle while the Marina berthing area is dredged on an 8 -year cycle, the dredging concept can provide additional time for Marina operation, during which time other long-term alternatives could be developed. Based on the 4- and 8- year cycles the concept could provide an additional 12 years of Marina operation. 11 The most recent dredging was a partial operation to 5 + 1. 12 Please note that a partial dredge of federal channel was performed in 2009 and previous to that in 1997. Chamfers were dredged by the City in 2001 and berths in 1997. San Leandro Marina Harbor Basin 4-11 ESA / 210461 Alternatives Study March 2011