4.2 Coastal Wetlands
San Dieguito Lagoon
San Dieguito Lagoon has an intermittently open inlet that is frequently subject to closure under existing
conditions. Historically, the inlet has been opened on an as-needed basis for flood control. Restoration
of the lagoon is planned for the fall of 2001 that includes maintaining an open tidal inlet.
The inlet is located about 1,500 feet north of the proposed Del Mar receiver site and over 2,000 ft south
of the proposed Solana Beach receiver site. No significant impact to water quality within the lagoon would
occur during receiver site construction given localized turbidity plumes.
Sediment transport modeling results predicted only short-term (about one year) substantial beach widening
near the lagoon entrance (Alternative C). However, under restored conditions, the project could result in
sedimentation within the lagoon. The maximum predicted project-related sediment increase rate for this
alternative is 12,500 cy over the four years post-restoration, with much of that in the first year. As part of
the project, SANDAG will implement a monitoring program to determine any increased rates of
sedimentation to the lagoon, or mouth closures, and will provide for mitigation of increased rates of
accumulation of sand or mouth closures attributable to the project (Section 2.5). This measure will ensure
no significant impact from the project on routine inlet maintenance.
Los Peasquitos Lagoon
The ocean inlet at Los Peasquitos Lagoon is mechanically opened each year (typically two to three times)
to sustain prolonged periods of tidal flushing. The ocean inlet is located about 750 feet north of the
proposed TorreyPines receiver site. As with the other lagoons, no significant impact to water quality within
the lagoon would occur from localized turbidity plumes.
Sediment transport modeling results indicate only short-term beach widening and limited sedimentation
offshore the inlet. The lagoon could experience some sedimentation from the project, and it is possible,
in the worst-case, that the action may necessitate one additional inlet opening in a year (approximately
5,000 cy). The monitoring program described in Section 2.5 and above would be suitable to verify no
significant impacts.
Regional Beach Sand Project EIR/EA
Page 4.2-5
99-69\SANDAG EIREA 4.1 to 4.13.wpd 7/17/00
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