4.2 Coastal Wetlands
Sediment transport modeling results indicated no substantial beach widening at the lagoon entrance nor
substantial sedimentation offshore the inlet (Appendix C). Therefore, potential lagoon closure due to
sandbar formationwould not be expected. However, the lagoon would experience sedimentation from the
project. The maximum predicted sediment increase over existing sediment patterns under this alternative
is 27,000 cy of sedimentation over five years, withover half that in the first year after construction. Project-
related sedimentation either would increase the volume dredged during the existing maintenance dredging
interval, or the dredging may have to be done more frequently. This impact is of most concern within the
first year after construction of the receiver site. As described for the Agua Hedionda Lagoon, the lagoon
monitoring program in Section 2.5 would be implemented to determine how much sand accumulation is
associated with the project and then mitigation would be provided as necessary.
Similar to the discussion for Agua Hedionda Lagoon, lagoon habitat quality is currently affected by
sedimentation and the necessary corrective action of maintenance dredging. Benthic organisms that inhabit
these shallow waters are quick to recolonize. No significant impacts would result from this action.
San Elijo Lagoon
The ocean inlet at San Elijo Lagoon is subject to frequent closure due to its relatively small tidal prism and
frequent blockage by cobbles. Mechanical excavations have resulted in periodic opening of the lagoon for
short durations spanning few to several months. The ocean inlet is located about 1,000 feet north of the
proposed Cardiff receiver site. As with the other lagoons, localized turbidity would not result in significant
impacts to lagoon water quality.
Sediment transport modeling results indicate beach widening at the lagoon entrance and offshore the inlet
(Appendix C). Therefore, there is the potential for the project to contribute to a more frequent closure of
the lagoon after mechanical opening. San Elijo Lagoon currently is mechanically opened three times a year.
It is possible, in the worst-case, that the project may necessitate one additional inlet opening in a year
(approximately 5,000 cy). As part of the project, SANDAG will implement a four-year monitoring
program to determine any increased rates of sedimentation to the lagoon and will provide mitigation for
mouth closures attributable the project (Section 2.5). This measure will ensure no significant impact from
the project on routine inlet maintenance activities.
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