4.2 Coastal Wetlands
Modeling predicts a potential worst-case increased sediment flow of approximately 62,500 cy from this
alternative over five years. Much of this material would be present in the first few years and taper off at
the end of five years. The lagoon inlet is continuously open as a result of jetties and routine maintenance
dredging. Sedimentation from littoral transport occurs within the lagoon under existing conditions,
therefore, the proposed project would incrementally increase the volume of sedimentation over that which
occurs naturally. Since maintenance dredge volumes historically have ranged from about 100,000 to
465,000 cy per year, the project's anticipated volume would not be anticipated to increase the frequency
of planned maintenance activities. It may slightly increase the cost of the dredging effort. As described in
Section 2.5, a lagoon monitoring program would be implemented as part of this project. The monitoring
program is designed to mimic the on-going monitoring as required under the Navy's USACOE permit.
SANDAG would provide for mitigation of any increased rates of sand accumulation determined to occur
as a result of the project above and beyond existing conditions, as determined by the USACOE and in
consultation with the resource agencies. Mitigation would consist of removing accumulated sediment
attributable to the replenishment project, by funding additional dredge activity during normal maintenance.
Previous monitoring in the lagoon indicates that fewer species and abundance of invertebrates occur in
areas that receive substantial sedimentation in comparison to less disturbed areas. The distribution of
eelgrass also is affected by sedimentation. Maintenance dredging routinely occurs in the outer basin where
benthic invertebrates within the maintenance dredge footprint recolonize rapidly. Maintenance dredging
occurs within set limits designed to avoid significant impacts to eelgrass. Impacts to lagoon fauna and
sensitive vegetated habitats as a result of sedimentation is not expected to be substantially different from
that which occurs in the lagoon under existing conditions. Therefore, project related impacts to lagoon
habitat quality would not be significant.
Batiquitos Lagoon
The ocean inlet at Batiquitos Lagoon remains open continuously due to jetties and maintenance dredging.
The ocean inlet is located about 1,000 feet north of the Batiquitos receiver site. No significant impact
would occur to water quality within the lagoon during construction given that turbidity plumes are
anticipated to be less than 100 to 500 feet downcurrent. Even under maximum current speeds they would
not extend far into the lagoon. If project related turbidity did enter the lagoon, particulate concentrations
would be low given the distance to the lagoon and rapid settling rate of the predominantly sandy material.
Regional Beach Sand Project EIR/EA
Page 4.2-3
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