Inlet Channel Maintenance Plan for Restored San Dieguito Lagoon

Coastal Environments has been monitoring the San Dieguito Lagoon since 1992 for Southern California Edison (SCE). SCE has the general objectives of preserving, enhancing, and enlarging the wetland habitat in the lagoon. These objectives require that the entrance channel to the lagoon remain open to tidal flushing to sustain water quality.

The need for inlet channel maintenance arose because the lagoon has a small tidal prism of 180-280 acre feet compared to its original state of 600 acres of salt marsh. Filling for construction has reduced the lagoon to 160 acres. Pre-restorative measurements of lagoon conditions from 1991-1994 allowed comparison between existing and restored lagoon conditions and simulation data. The Consensus plan to restore the lagoon will increase the potential tidal prism to 135-150% of the existing tidal prism.

The dynamics of small, shallow lagoon inlets are highly complex. Lagoon hydrodynamic behavior depends on channel bottom topography, which changes rapidly in response to river floods, tides, and wave-driven sand transport. A comparison between the existing lagoon and the restored lagoon was made, including tidal prism and influx volume of sediments. The restored lagoon will require maintenance.

A dredging plan was outlined to include periodic maintenance dredging, implementation, scheduling, and sediment disposal locations. A monitoring plan including topographical surveys, water-level measurements, and water-quality measurements was designed.

Client:

Southern California Edison

Client Contact:

Southern California Edison
2244 Walnut Grove
Rosemead, CA 91770