4.4 Biological Resources
Direct Impacts of Dredging
Approximately 330 acres of surface area would be needed to provide 2 million cy of sediment for
Alternative 1a from Oceanside to Imperial Beach. There are approximately 53 miles of coastline with a
variable shelf width at depths of 40 to 80 feet, or about 0.6 mile offshore. For this alternative, this acreage
represents less than two percent of the available shelf habitat. If SO-7 is expanded and SO-9/SO-6 are
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eliminated, the surface area would be approximately 318 acres which is slightly less overall. There would
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be no change to the impact conclusion regarding direct impacts.
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The dredging of sand sediments from the borrow sites would impact marine biota by the direct removal of
the organisms and alteration of habitat. All of the benthic infauna, epifaunal, and demersal organisms in the
area of excavation would be displaced or destroyed. The extent of the loss and/or displacement is directly
proportional to the area and amount of sediment removed at each site. As discussed in Section 3.4, the
infaunal and epifaunal communities within the dredge areas consist of broadly distributed species and none
would be significantly reduced at the population level from the loss of individuals within the dredge areas.
Mobile epibenthic macroinvertebrates and fish would be expected to move from areas being actively
dredged, but these species would not be lost to the ecosystem nor would migration patterns be affected.
This would be considered an adverse impact, but not significant.
Epibenthic invertebrates and fishes that feed upon benthic biota would suffer a localized, short-term loss
of prey. However, because the active area being dredged would be small and localized, short-term loss
of food on these organisms is judged to be adverse, but not significant.
Dredging at borrow sites would also have some beneficial aspects because many of the infaunal organisms
recruit rapidly to disturbed and newly exposed sediments. This produces heterogeneity in the environment,
which can contribute to increased biodiversity of the community. Furthermore, most epibenthic
invertebrates and demersal fish are opportunistic in their feeding. They could be attracted to disturbed
areas where feeding opportunities may be increased by dredging activity.
Concern has been expressed that borrow site excavations have the potential to trap organic material and
drift kelp. The accumulation and decay of excessive organic material could lead to altered water quality
parameters and possibly degraded benthic biota. However, these concerns have proven to be unfounded
for open coastal areas and in harbors with good tidal flushing (Appendix D). All of the borrow sites are
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Regional Beach Sand Project EIR/EA
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