ACTIVE BEACH PROCESSES AT SAN ONOFRE STATE BEACH, CA

Hundreds of millions of people visit California’s beaches every year – 550 million in 1995 alone! It is important to understand the processes which shape such a heavily used natural resource. Our study investigates active beach processes operating at San Onofre State Beach in San Diego County, California. San Onofre is notable for cobble beach cusps, which show unusually pronounced grain size sorting, and for the presence of San Onofre Nuclear Generating Station (SONGS). From September through November of 2002, we made observations of beach cusp morphology and beach profiles surrounding SONGS. Beach cusp spacings were found to be variable through time, and were consistent with cusp formation by edge wave forcing. The centers of cusps were found to have larger grain size and sphericity, grading to sand at the cusp edges. Beach volume did not change significantly north of SONGS, but decreased by 26% to its south. This can be explained by seasonal beach changes, combined with blockage of longshore sediment transport by SONGS. In short, San Onofre State Beach is significantly influenced by both wave dynamics and the presence of SONGS.