4.4 Biological Resources
The variation in sand replenishment would also have a relative difference in potential indirect sediment
transport impacts, although there would be no significant indirect sedimentation impacts to marine resources
under Alternative 2. The key difference under Alternative 2 would be the change in the patterns of potential
sedimentation risk. Under Alternative 1, areas of greater sedimentation risk were identified off South
Oceanside, southof North Carlsbad, near Batiquitos, near Moonlight Beach, north of Solana Beach, north
of Del Mar, and off Imperial Beach. Each of these same areas is addressed below to allow for comparison
of alternatives. There would be no measurable sedimentation at resources near the South Carlsbad South
receiver site, and it is not discussed further in this text (Appendix D). Indirect sediment impacts at Torrey
Pines, Mission Beach and Imperial Beach would not be significant even with the greater quantity of sand
associated with this alternative (refer to the 3 million cy analysis at these three receiver sites in Appendix
D).
It should be noted that this complete alternative is not evaluated in Appendix D. The three southern-most
sites are identical to the 3 million cy alternative that is evaluated in Appendix D. Other significance
conclusion are based on predicted patterns as derived from the 2 million cy analysis in Appendix D,
professional judgement and worst-case assumptions. The intent is to provide full disclosure of the potential
worst-case indirect impacts.
Potential Indirect Sedimentation Impacts Near Oceanside. Marine resources near South Oceanside
are limited as most of the nearshore area is sand. Sand was mapped previously by the Navy at -10, -20
and -30 isobaths (Department of the Navy 1997a, 1997b). Isolated scattered rock identified by
commercial fisherman have been verified in one location; specifically, at the southern end of the receiver
site where worst-case sedimentation risk was predicted by the model for Alternative 1. Under Alternative
2, the amount of sand would be greater than under Alternative 1 but the receiver site would be 5,600 feet
longer (over one mile to the north) and the beach width after sand placement would be 60 feet narrower.
While the replenishment material would enter the seasonal sand cycle and result in some indirect
sedimentation, the indirect impact would not be any greater than assumed under Alternative 1. This is
because the material on the narrower, longer beach would be relatively less exposed to the dynamic system
and would not erode as fast. Also, it would be spread further north and would not likely result in
sedimentation risks greater than those identified under Alternative 1 (Moffatt & Nichol 2000d).
Mapped hard substrate is primarily cobble and rock relief with no sensitive species. Two locations with
scattered sea fans are at the model-predicted seaward edge of the area of higher sedimentation risk.
Empirical data from replenishment projects in 1983 and 1988 indicate no obvious sedimentation at the
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