4.4 Biological Resources
Kelp beds occur from about 1,200 to 4,000 feet offshore, which is outside the distance that turbidity
plumes would be expected to travel offshore. In the unlikely event that turbidity did extend that far
offshore, the particulate concentration would be so low as to have a negligible effect on the kelp bed.
Therefore, no significant indirect impacts to kelp beds are anticipated from turbiditygenerated fromreceiver
site construction.
Nearshore vegetated reefs may be impacted by reduced light transmittance and siltation associated with
turbidity plumes. Turbidity will be controlled by the construction of longitudinal dikes and would not be
expected to exceed concentrations that naturally occur in turbid nearshore waters during higher wave or
storm conditions. Similarly, turbidity would not be anticipated to have significant impacts on benthic
invertebrates offshore the receiver sites and within the distance of the expected turbidity plumes. Limited
information from recent beach replenishment projects reported 43 mg/L at the discharge location when the
discharged sediments had a silt/clay content less than 10 percent. Based on the sandy nature of the borrow
site sediments and use of longitudinal dikes to control turbidity, it seems reasonable that suspended
particulate concentrations would be less than 100 mg/L offshore the discharge location and decrease with
increasing distance from that location at the receiver site. As adults, mussels and oysters can tolerate
suspended matter in the range of 100 to 1000 mg/L over reasonably short exposure times. For larvae and
juveniles the effects appear to be negligible below 200 mg/L and slowly increase to critical levels at about
750 mg/L. Juvenile rock lobsters tolerate suspended particulate concentrations of at least 360 mg/L for
several days as well as exposure to sand. Thus, marine invertebrates adapted to living in naturally turbid
nearshore waters have relatively broad tolerance levels that would not be expected to be exceeded by the
project.
Sediment Transport. Fill material placed on individual receiver sites would eventually be washed by
waves and redistributed offshore and alongshore through natural processes. There is the potential for sand
introduced into the system to indirectly impact sensitive resources if material deposits on those resources
at sufficient depth and with persistence to result in irreversible removal, disturbance or destruction of that
resource. As defined in Section 4.4.2, sensitive indicator species consist of surfgrass, feather boa kelp, sea
fans, sea palms, and giant kelp.
Evaluating potential indirect sedimentation impacts is complex and the impact conclusions must be
determined in light of the dynamic ocean system, where season fluctuation of up to three feet of sand has
been monitored and where historic beach replenishment activities have occurred in many of the same
locations as proposed by the Regional Beach Sand Project; with an understanding of the life history of
Regional Beach Sand Project EIR/EA
Page 4.4-27
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