California Sea Grant College Program

The Southern California Bight (SCB) is a dynamic ocean environment heavily influenced by anthropogenic activities and their associated contaminants. This dissertation utilizes the Regional Oceanic Modeling System (ROMS) to explore several coastal processes relevant to contaminant transport and water quality. In this work, results from an 8-year integration of ROMS in the SCB are assessed against a number of observational datasets to demonstrate the model's ability to simulate a realistic ocean environment on multiyear, interannual, seasonal, and eddy time scales. The model is further validated against measurements off San Pedro Bay on annual mean, seasonal, and subtidal time scales. Using an Eulerian tracer transport model, the mean residence time of San Pedro Bay was found to be 1.6 days, and most of the residence time distribution functions matched closely with that predicted by an ideal well-mixed system. Mean residence times were weakly correlated with subtidal flows, such that shorter mean residence times were associated with stronger subtidal upcoast flows around the bay boundary. Division of the bay into sub-regions showed that the inner bay is generally more retentive than the outer bay, but the difference in mean residence times was small, supporting the well-mixed aspect of circulation within the bay. The dynamics of episodic stormwater plumes, a significant source of contaminants in the SCB, were investigated stochastically using ROMS to simulate multiple, average-sized discharges from the Los Angeles and San Gabriel Rivers. Simulated plumes showed generally good agreement with plumes observed by remote sensing and ship surveys, in terms of spatial and temporal scales. Plumes were found to travel primarily in an alongshore direction following local surface currents at subtidal frequencies. Dispersion rates calculated for plume waters were higher than those of the open ocean, likely due to the increased horizontal shear of coastal waters. Plume impact areas extended 10s of km along the coast for up to 10 days and depend on the dilution level of concern. In addition to advection and dispersion by local currents, the buoyancy of the freshwater plumes was found to be a major factor in offshore advection of the stormwater.