Application of airborne LIDAR for seacliff volumetric change and beach-sediment budget contributions

Coastal seacliff erosion in California threatens property and public safety, whereas coastal beach erosion threatens the coastal tourism economy. While coastal rivers, seacliffs, and gullies supply the majority of littoral material to California beaches, the relative contributions of these sources are coming into question. These beach-sediment sources must be accurately quantified to formulate proper solutions for coastal zone management. This study evaluated the seacliff and coastal gully beach-sediment contributions to the Oceanside Littoral Cell using airborne LIght Detection And Ranging (LIDAR). Seacliff and gully beach-sediment contributions were compared with coastal river beach-sediment contributions estimated in previous studies. This study took place over a relatively dry period from April 1998 to April 2004. The results indicate that seacliffs provided an estimated 67% of the beach-size sediment to the littoral cell, followed by gullies and rivers at 17% and 16%, respectively, over the period of the study. The total volumetric seacliff erosion rates were used to back-calculate average annual seacliff face retreat rates for the study period. These rates ranged from 3.1 to 13.2 cm/yr and averaged 8.0 cm/yr for the Oceanside Littoral Cell. Comparison of these results to previous studies suggests that the relative seacliff sediment contributions may be higher than previously thought. Conversely, beach-sediment contributions from gullies were significantly lower-compared with previous studies. This is likely because of the episodic nature of gullying and the relatively dry study period. Nevertheless, the results of this study indicate that seacliff sediment contributions are a significant sediment source of beach sand in the Oceanside Littoral Cell, and the relative annual seacliff beach-sand contribution is likely higher than previous studies indicate.