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0127im.jpg){kind=tracking} 3.2.2 Turbidity
The proposed beach fill material may contain up to 35 percent fine sediment. The fine
sediment, as it is washed into the surfzone will create a temporary turbidity plume that
could extend up or down the coast and offshore depending on currents. For example,
turbidity plumes that extended 2,600 to 4,000 ft. downcoast and 50 to 300 ft. offshore
were observed from a beach nourishment project at Surfside and Sunset Beaches in
Orange County in which approximately 1,600,000 cubic yards of sediment with a
silt/clay content of 11 to 15 percent was pumped onto the receiver beaches (Corps
1997). On brief occasions, plumes were noted as far as 2,000 ft. offshore and up to
2 miles downcoast. In another similar project, turbidity was monitored from a beachfill
project at Ponto Beach, California. Approximately 20,000 cubic yards of material with
20 percent fines generated a plume 5 miles long that lasted for one day (Sherman et al.
1998).
Turbidity can reduce the light available for photosynthesis for phytoplankton, attached
algae, and marine grasses. Mechanical or abrasive action of suspended silt can
negatively impact invertebrates by clogging their gills and impairing proper respiratory
and feeding activity (Snyder 1976). Extended exposure to extremely high levels of silt
could harm fishes, but most fishes exposed to turbidity in the open ocean would be
expected to leave the area before they would suffer damage from turbidity plumes.
Turbidity also could impact visually foraging piscivorous seabirds such as California
brown pelicans and California least terns by making it difficult for them to see their prey.
Brief pulses of turbidity for a few days would not be expected to significantly impact
nearshore communities. The impacts to kelp of a broken sewer line at Pt. Loma in San
Diego were monitored. The accident caused turbidity in the kelp bed to be elevated for
weeks, but no impact to the kelp bed was observed (L. Deysher, personal
communication 2001). Therefore, elevated turbidity for a period of a week or less would
not be expected to have significant adverse impacts on kelp. However, extended
turbidity plumes that affected large portions of sensitive habitats such as kelp beds for a
period of weeks may have significant adverse effects.
3.2.3 Disturbance by Equipment and Beach Fill Activities
In most cases, the sand will be delivered to the receiver beach by truck. Earthmoving
equipment such as bulldozers then will push the sand below the low tide line or
construct a berm on the beach or sand dike along the revetment.
The movements of trucks and equipment could damage the eggs of listed
groundnesting birds such as the California least tern and western snowy plover.
Grunion eggs could also be damaged. Any damage to the eggs or nests of sensitive
bird species or substantial loss of grunion eggs would be a significant adverse impact.
The noise and activity involved in the placement of sand on receiver beaches could
have an indirect impact on nesting birds by disturbing them and interfering with their
breeding activities. Disturbance to California least terns or western snowy plovers
during the breeding season would be a significant adverse impact. Project activities
33
3208 Bio Report
06/12/02
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