Coastal Environments conducted a study to analyze sediment transport in the vicinity of the Agua Hedionda Lagoon, located in Carlsbad, California. Specific technical tasks in this study included:

1. Review sediment transport in the vicinity of Agua Hedionda Lagoon
2. Estimate shoreline erosion rates
3. Evaluate the effect of the power plant and the lagoon on the natural transport and deposition of sediment to the shoreline
4. Develop four sediment placement options
5. Identify stable disposal sites north and south of the lagoon. The results of the technical tasks were used to develop an optimal disposal strategy for sediments dredged from the Agua Hedionda Lagoon.

The SDG&E Encina Power Plant is located adjacent to the Agua Hedionda Lagoon. The power-generating units take water from the lagoon for cooling purposes, which reduces the volume of water available to flush the lagoon inlet, resulting in sand accumulation (138,000 yd3/yr) within the Outer Basin of the lagoon. SDG&E has been dredging the Outer Basin of Agua Hedionda Lagoon since construction of the plant in 1954 to remove trapped sediments and maintain tidal circulation in the lagoon.

Optimal placement of the sediments dredged from the lagoon was required to offset power plant effects of trapping the beach sand. Results of the analysis were used to evaluate disposal options for sediments dredged from the lagoon. The principal results showed that

1. The power plant operation has had a short-term effect on local beaches by altering the natural coastal processes near the lagoon and increasing the lagoon sedimentation rate
2. The local effect of the power plant was at a maximum near the in-take channel and decreased with distance
3. Carlsbad Submarine Canyon altered the local wave regime and decreased the northward longshore transport at Carlsbad compared with Oceanside
4. Maximum recreational benefits were attained by placing the sand on all three Carlsbad beaches adjacent to the lagoon-named North, Middle, and South beaches.

San Diego Gas & Electric Co.
California Coastal Commission
City of Carlsbad

Coastal Oceanographic Engineering

Wetland Restoration