4.2 Coastal Wetlands
Alternative 2
4.2.3
Impacts of Alternative 2a
San Luis Rey River
Sediment from the beach fill at South Oceanside is predicted to migrate northward to the vicinity of the San
Luis Rey River mouth after sand placement and potentially widen the onshore beach at this location
approximately one year after sand placement. Because the existing berm that crosses most of the San Luis
Rey River mouth is already at a higher elevation than the predicted contribution from the proposed action,
the migrating sand would not be anticipated to impact the overall configuration of the river mouth.
Stormwater discharge from the river is constrained by flow through eight, 36-inch-diameter pipes that pass
under Pacific Street. The initial small increase in beach width at this location would be reduced over time
as the sand moves back along the shoreline in a southerly direction. The predicted temporary increase in
sediment at this location would not be anticipated to constrain river runoff, therefore, additional maintenance
is not required with implementation of the proposed project.
The City of Oceanside Streets Division is responsible for maintaining the Pacific Street stormwater outlet
on an as-needed basis for flood control. Therefore, no adverse impacts would be anticipated upon
implementation of the proposed action.
Loma Alta Creek/Buena Vista Lagoon
The impacts to these locations would be no worse than under Alternative 1. Impacts would be less than
significant.
Agua Hedionda Lagoon
Under this alternative, there would be no sand placement at the North Carlsbad receiver site but the South
Carlsbad sites (North and South) would receive over twice the volume as under Alternative 1. Given this
configuration, the sand placement would be about one mile from the lagoon mouth. Turbidity plumes would
be localized and there would be no significant impacts. Modeling predicts a potential worst-case increased
sediment flow of approximately 57,500 cy of sediment over five years, of which most would occur in the
Regional Beach Sand Project EIR/EA
Page 4.2-7
99-69\SANDAG EIREA 4.1 to 4.13.wpd 7/17/00
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