Spatial and temporal trends in California coastal cliff retreat
Zuzanna Swirad, Adam P. Young
Abstract
Airborne LiDAR datasets were used to measure erosion and retreat along 866 km of California coastal cliffs between 2009–2011 and 2016. Erosion exceeding the level of detection was observed at 55% of cliffs. State-averaged cliff face and top retreat rates were both 0.06 m yr−1, and varied alongshore, with more erosion in northern California compared to southern and central California. Retreat rates were higher for unarmored cliffs and cliffs fronted by sandy beaches. Mean cliff top retreat rates were lower than in previous studies conducted between the 1920s–1930s and 1998/2002, and between 1998 and 2009–2011. However, the average cliff face retreat rates and statistical distributions were similar (r2 = 0.99) for the 1998 to 2009–2011 and 2009–2011 to 2016 time periods. No significant correlation was found between cliff erosion rates and environmental factors such as rock hardness, rainfall, groundwater, waves, and relative sea level change. However, the highest cliff face retreat rates (>1 m yr−1) occurred at locations with weak rocks.