4.4 Biological Resources
depths under this alternative would be under the heights of the reefs at this location and there would be no
significant impacts to remaining vegetation.
Partial sedimentation is, however, predicted under worst-case conditions at two areas supporting giant kelp
in deeper water. These two substrate locations are located between -25 and -35 feet MLLW offshore of
Pill Box reef, adjacent to, but not within, the areas of more persistent kelp as indicated by the 1997 kelp
canopy in Figure 4.4-8. These two substrate areas consist of both sparse juveniles and giant kelp and total
just over one acre. Based on the worst-case model predictions, these two reefs would receive partial
sedimentation, not burial, for no more than one year under above average wave conditions. The temporary
loss of kelp in non-persistent kelp bed areas would not be a significant impact. Substantial, persistent
sedimentation is not predicted for the more offshore, historical kelp beds as indicated by the 1997 kelp
cover in Figure 4.4-8 and there would be no significant impact at these locations.
Potential Indirect Impacts North of Del Mar. Sand is the predominant habitat in the vicinity of the
Del Mar receiver site. Historic kelp bed locations indicate that most hard substrate is located further south
of the receiver site. Commercial fisherman indicate scattered rocks south of the site at depths of
approximately -25 feet MLLW, but the 1997 historic kelp canopy does not enter into the area mapped
in Figure 4.4-9. Intertidal surfgrass is located south of 15th Street, which indicates hard substrate as well.
The nearest hard substrate to the north includes commercial fishermen identified areas of scattered rock
near the mouth of San Dieguito Lagoon, historic kelp bed areas north of the lagoon, and intertidal and
nearshore reef north of the lagoon. The identified scattered rock off the lagoon mouth was surveyed in
February and March 2000 and the mapped hard substrate is shown in 4.4-9.
Under worst-case model predictions, the only areas of hard substrate with sediment risk are the scattered
rock locations identified by commercial fishermen. All hard substrates within this area included cobble and
rock relief without sensitive resources. They are vegetated only with opportunistic species such as coralline
algal turf. Given the lack of sensitive species, there would be no significant indirect impacts at this location.
Intertidal and nearshore reef areas to the north off San Dieguito Lagoon and to the south of the receiver
site are not predicted to be at risk from substantial sedimentation. Intertidal surfgrass beds located south
between the Del Mar and Torrey Pines receiver sites (not shown in mapped boundary of Figure 4.4-9) are
predicted to experience shallow sedimentation (less than one-half foot) under above average wave
conditions, but not under average wave conditions. That level of sedimentation would not be expected to
result in any long-term significant impacts to the surfgrass beds because they occur on higher relief reef.
Page 4.4-36
Regional Beach Sand Project EIR/EA
99-69\SANDAG EIREA 4.1 to 4.13.wpd 7/17/00
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