4.2 Coastal Wetlands
Mission Bay
The proposed Mission Bay receiver site is almost one mile north of the entrance to Mission Bay. Turbidity
plumes would be very localized (approximately 80 feet) and even under maximum current conditions the
jetty would prevent significant impacts to the bay. Sediment transport from the receiver site is predicted
to migrate south toward the jetty at Mission Bay; however, the jetty is so long that sediment from this action
would not likely be transported into the bay. Some small, incremental quantity of sand may move through
the jetty and contribute to the existing shoals in the channel, but the project's contribution would not be
measurable given other sand movement.
Tijuana Estuary
No significant impacts to water or habitat quality within the Tijuana Estuaryare anticipated from the project.
The receiver site is more than one mile north of the inlet and turbidity plumes are calculated approximately
135 to 80 feet. Turbidity plumes would not be expected to enter the wetland, even under maximum current
speeds. Migration of sand towards the Tijuana River mouth would be unlikely given the net longshore
sediment transport rate being to the north. Therefore, no significant impacts to the estuary are anticipated
from project-related sedimentation.
Mitigation Measures for Alternative 1a
Turbidity would not significantly affect any coastal lagoons so no mitigation would be necessary. As
described in Section 2.5, a monitoring program would be implemented at several lagoons to verify whether
or not project-related sediment would result in increased rates of sand accumulation or mouth closures
attributable to the project. SANDAG has committed to fund the removal of sediment or inlet openings as
determined to be appropriate by the USACOE and in consultation with the resource agencies. No further
measures would be necessary.
Impacts/Mitigation Measures for Alternative 1b
Under this alternative, construction would occur over a longer time period, but less sand would be placed
most receiver sites. Potential effects at individual lagoons would not be any greater under this construction
variation. The monitoring program in Section 2.5 would be implemented to either verify no significant
impact or institute mitigation as necessary.
Page 4.2-6
Regional Beach Sand Project EIR/EA
99-69\SANDAG EIREA 4.1 to 4.13.wpd 7/17/00
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