Numerical Modeling Studies of San Elijo Lagoon Restoration Project

The San Elijo Lagoon Ecological Reserve is located within the City of Encinitas in San Diego County, California. The Reserve provides habitat for sensitive, threatened, and endangered species, as well as recreational opportunities. Due to development, the ecological function of the lagoon has been degraded. The San Elijo Lagoon Restoration Project is an effort to restore the lagoon functions and values. Four new alternatives are proposed. Two of them will use the tidal inlet at its current location and the other two will have a new, wider and deeper tidal inlet located south of its current location. RMA2 tidal and flood hydrodynamic modeling studies were performed. The results indicate that alternatives with the new tidal inlet can provide better tidal flushing, support a broader vertical range of salt marsh habitat, significantly lower the flood water level, and avoid flooding of a perimeter road during the 100-year storm event. RMA4 water quality modeling results indicate that alternatives with the new inlet would dramatically reduce the residence time, the duration of bacteria exceedance in the Lagoon and nearshore ocean, the salinity concentration recovery time after rain events, the travel time of nutrients and fine sediment through lagoon, and sedimentation in the Lagoon.