Modeling of an Erosional Hot Spot at Ocean Beach, California

(Fengyan Shi, James T. Kirby, Center for Applied Coastal Research, University of Delaware, Newark, DE 19716,

Daniel M. Hanes, Pacific Science Center, Coastal and Marine Geology Program, USGS, 400 Natural Bridges Drive, Santa Cruz, CA 95060)

Ocean Beach, California is an ocean-exposed beach adjacent to the mouth of the San Francisco Bay. The shoreline at Ocean Beach has been experiencing areas of erosion for decades with recent severe effects focused on an erosional hot spot near the reattachment point of the ebb tidal delta at Ocean Beach. In this study, we couple a wave model, a circulation model and a sediment model to predict waves, nearshore circulations and sediment transport at the mouth of the San Francisco Bay, with emphasis on Ocean Beach. Far-field motions are taken into account by incorporating large-scale forcing into the nearshore modeling system. The accuracy of the coupled model is demonstrated by comparisons with field measurements conducted in the summer of 2005 and the winter of 2006. The model results indicate that surface waves from a large range of incident wave directions tend to focus on a very narrow region at the hot spot location. The wave focusing pattern and the littoral transport are responsible for the hot spot evolution.