Goals: The Southern California Beach Processes Study (SCBPS), sponsored by the U.S. Army Corps of Engineers and the California Department of Boating and Waterways, is monitoring and modeling beach erosion, providing the knowledge base for more effective local and regional beach management.
Ongoing observations of beach erosion and accretion (obtained with GPS-equipped aircraft, personal watercraft, all terrain vehicles, and hand-pushed dollies) are available to beach management agencies, and are used by SCBPS scientists to test and develop models for beach erosion.
Sand Level Changes: SCBPS has collected insitu and remote observations of sand level changes on nourished and natural beaches. Airborne topographic LIDAR (Light Detection and Ranging) has been used since 5/2002 to survey repeatedly the beach between the low tide waterline and the backbeach from Pt LaJolla to Dana Point (about 79 km), and from the Mexican Border to Long Beach (about 170 km). The surveys include the approximate times of maximum (early Fall) and minimum (early Spring) beach width, and are used to estimate alongshore variations in the seasonal cycle of changes in beach width and sand volume, and to identify longer-term erosional trends. Specialized LIDAR classification/editing techniques are being developed in collaboration with the University of Texas.
The spatially extensive and dense (multiple data points per square meter) but temporally infrequent LIDAR surveys are supplemented with more frequent surveys at two focus sites, separated by approximately 40 km, selected for their contrasting exposure to sea and swell. Monthly surveys, spanning several km at Torrey Pines Beach (begun 2/2001 to study a beach nourishment project) and San Onofre Beach (begun 5/2005), are obtained above the low tide waterline with a GPS-equipped all terrain vehicle. Surveys are extended to 8-m depth twice a year, using GPS-equipped personal watercraft.
The insitu monthly and the LIDAR surveys have similar vertical accuracy, less than 10 cm bias and less than 10 cm standard deviation. After quality control, digital data are available to the Army Corps of Engineers and other agencies concerned with beach management, and data products are available through the SCBPS website.
Waves: A program objective is to better understand the relationship between waves and changes in beach sand level, and to include this understanding in models that can be used in beach management. Wave observations from the Coastal Data Information Program (CDIP) are being combined with a numerical model to estimate the nearshore wave field with high alongshore and temporal resolution. This task is complicated in Southern California owing to the complex ocean floor topography and the shadowing effects of offshore islands that can cause large variation in wave characteristics over small longshore distances. CDIP continues to validate and improve wave transformation models.
Models For Beach Erosion: SCBPS is developing and testing models relating waves and beach erosion in Southern California. Field validated models will allow engineers to predict future beach evolution more confidently, and thus to make more informed decisions. For example, the model could be used to simulate erosion of a beach nourishment under different scenarios for the intensity and frequency of future storms.