UC San Diego

The nature of the short-term processes that govern long- term seacliff retreat remains poorly constrained, primarily because conventional approaches, such as digital and softcopy photogrammetry and to some degree airborne LIDAR used to monitor these processes focus more on the recession of the cliff top due to limited coverage of the cliff face. Terrestrial LIDAR, however, is not limited by oblique viewing angles and accurately records wave undercutting, groundwater sapping, and the evolution of the cliff morphology to a precision of 7-10 cm. Here we present a detailed 3.5 year times series with numerous high resolution digital terrain models (DTMs) derived from terrestrial LIDAR data for three near vertical cliff sites in the southern end of the Oceanside Littoral Cell to resolve better the processes responsible for cliff erosion with minimal overprinting by natural processes or anthropogenic changes. The results reveal both marine and subaerial processes operate in the study area with a spatial focus on areas of groundwater saturation caused by changes in facies. In addition, we present a new detailed approach to determining the sediment contribution from cliff erosion using LIDAR volumes derived for each geological formation and a cutoff grain size of 125 [mu]m. Erosion of the three sites, a total length of 350 m, liberated 4,697 m³ of sediment in a 3.5 year period, with 3,230 m³ above the cut-off grain size. Applying a littoral cutoff diameter (LCD) reduces the sediment input to the littoral environment by 31%