Sea water intrusion into a fresh water forebay due to wave action

Abstract

Sea water intrusion adversely affects the water quality of the Salinas River Lagoon near Castroville, California. Bench levels indicated that the forebay is above mean sea level; however, additional investigations showed that wave action maintains a water level beneath the beach which is above mean sea level and the forebay. Wave action produces a net landward gradient resulting in underflow from the sea into the forebay. The quantity of sea water added to the lagoon was calculated from salt balance and from gradient-transmissibility relationships. The amount of sea water underflow calculated by these two independent methods was 24.5 and 25.1 acre-feet, respectively. Tides, wave action, and density differences between fresh and salt water should be considered in the interpretation of hydraulic relationships between coastal lagoons and the sea.