Relocation of the San Elijo Lagoon Inlet
The San Elijo Lagoon is a coastal lagoon located in the city of Encinitas, San Diego County, California. It is characterized by shallow depths (up to 4 ft) and small tidal prism. Some of the problems associated with the low flow volume entering the lagoon are low water quality, lack of productivity, high sedimentation rates, and temporal inlet closure.
The inlet relocation project emerged from a need to replace the existing Highway 101 bridge that was deteriorating.
Expected benefits of inlet relocation and associated lagoon dredging included disposal of dredged material as beach nourishment; increased circulation; better water quality; reestablishment of migratory bird habitat; and improved open space for recreational use.
Three main inlet alternatives were proposed and analyzed. The option of removing the railway berm and implementing a 3600-ft railroad bridge was considered to further increase the lagoon system circulation.
To select the best option, existing vegetative cover, circulation patterns, sedimentation rates, sediment transport, volume of dredged material, recreational use, and important species present in the area were analyzed through fieldwork, aerial photography, and numerical modeling.
For modifications associated with the highway and railroad, an engineering calculation approach was undertaken.
CE concluded that relocating the inlet to the central part of the lagoon, just south of the sewer outfall pipe, was the best hydrodynamic option. This would necessitate the removal of the existing railway berm.
Some of the features of this option included a new 300-ft highway bridge, elevation of the highway at areas subject to flooding, railway elevation, and extensive dredging inside the coastal system.
The second most feasible option was to leave the inlet in its present location and undertake extensive dredging activities. This is a less complicated option.