Three years of weekly coastal cliff erosion monitoring with lidar in southern, CA

Abstract:

Wave erosion is a fundamental process of coastal cliff morphology, yet field studies measuring quantitative relationships between waves and cliff erosion are rare. This study explored the roles of waves and rainfall with three years of ~weekly lidar observations for 2.5 km long southern California coastal cliff. Over 4300 erosion events were detected ranging up to 885 m³ (mean 3.3 m³). Cliff retreat varied in space and time, and several erosion hotspots experienced mean profile retreat rates of 0.9 m/yr, an order magnitude higher than the 0.09 m/yr mean over the entire study site, while 68% of the cliff face experienced no significant change over the study period. In one time interval the mean cliff retreat was 0.034 m, while in 141 intervals the mean retreat rate was less than one mm. Cliff erosion rates, incident waves, wave-cliff impact, and rainfall were all elevated during winter months, when beaches fronting the cliffs were most eroded. Cliff-base wave observations were used to validate modeled cliff base wave impact heights and develop wave-cliff interaction metrics. The 154 ~weekly observations of cliff changes were compared with metrics of wave impacts and rainfall. Upper cliff erosion was correlated with rainfall, and lower cliff erosion with wave impacts. The results highlight the high temporal and spatial resolution observations needed to resolve and quantify wave-driven erosion processes in coastal cliff retreat models.