Coastal cliff erosion in California 2009-2016

Abstract:

Rocky coasts comprise ~70% of the 1,700 km California coast and their erosion currently threatens clifftop infrastructure in many parts of the state. Sea level rise is expected to exacerbate the problem. An assessment of contemporary cliff retreat rates, identification of erosional hotspots, and understanding the processes that drive cliff erosion are essential for coastal management and building resilient communities.

We present results for one of the largest cliff erosion studies to date and the first study to quantify coastal cliff erosion for the entire coast of California using high-resolution (≤m) data. We quantify cliff changes using airborne LiDAR collected in 2009-10 (NOAA Coastal Services Center) and 2016 (USGS West Coast El-Nino LiDAR), a semi-automated method to delimit cliffs, and machine learning methods to separate cliff erosion and talus deposits from vegetation dynamics. We analyze alongshore patterns in cliff retreat and compare contemporary erosion rates with previous historical regional-scale approximations (1930s to 1998, and 1998 to 2009) to examine temporal changes and patterns in erosion rates. We also explore relationships between cliff erosion, geology, wave intensity, rainfall, and cliff armoring. The results will help inform decision making and serve as a calibration/validation dataset for modelling rocky coast erosion under changing climate.