Scripps Institution of Oceanography

Seasonal airborne and ground-based observations of sand level changes were made along the coast of southern California from 2001 to 2008. Hourly, high alongshore spatial resolution wave estimates from a network of wave buoys and a spectral refraction wave model complement the sand level change data. Water returns from the ocean surface were removed from the airborne lidar elevation observations with a new method using tide and wave data, which was validated with concurrent in situ surveys. The resultant sand levels show high alongshore variability in seasonal shoreline position change along the 120-km survey region. Alongshore variability in wave energy, geologic factors, and sand grain size are hypothesized to control the alongshore variability of the seasonal shoreline change magnitude.

Monthly or more frequent ground-based surveys at four selected focus sites show seasonal shoreline and bathymetry change, with winter shoreline erosion and offshore bar development, and summer shoreline accretion and the loss of the offshore bar. Analysis of surveys completed after a small beach nourishment at Torrey Pines Beach showed the presence of the nourishment through more than one full seasonal cycle.

Observations from Torrey Pines Beach show the dependence of shoreline change on the initial shoreline position and the wave forcing. The observations motivated the development of an equilibrium shoreline change model, which accurately reproduces the observations with four free parameters. With at least two years of monthly surveys or multiple years of appropriately-timed biannual observations used to determine the free parameters, the model accurately predicts withheld observations and is applied at the additional survey sites. Ongoing work includes applying the model at additional locations and investigating the relationship between the tuned parameters and geologic factors.