Three years of weekly observations of coastal cliff erosion by waves and rainfall

Abstract

Erosion of a 2.5 km-long sedimentary coastal cliff by waves and rainfall is explored with three years of weekly observations. A truck-mounted lidar resolved the fronting beach and convoluted surface of the ~10–25 m high cliffs. Volumes of 4362 cliff erosion events ranged up to 885 m3 (mean 3.3 m3). The three-year cumulative erosion was clustered and alongshore variable. Cliff base wave impact heights were estimated with a wave model and empirical runup formula, and validated with cliff base observations. Cliff erosion rates, incident wave heights, wave-cliff impacts, and rainfall were all elevated during winters. The high temporal resolution of the multiyear dataset is unique, and allows separation of erosion from waves and rainfall by, for example, isolating time periods with no rainfall and high wave runup. Upper cliff erosion was best correlated with rainfall (r2 = 0.57), and lower cliff erosion with wave impacts (r2 = 0.56).