Sand budget failure underlies coastal erosion on the west coast of South Africa

Abstract

<title>Abstract</title> Current trends in coastal erosion combined with projected climate change impacts place half of the global sandy beaches at risk of extinction. Approximately 190 million people are likely to experience coastal environmental risks by 2100, and mitigation of the risk related to coastal erosion requires insight into the underlying causes. Here we use a multi-proxy approach to determine the cause of coastal erosion on the west coast of South Africa. Erosion trends were determined using satellite analysis for a storm event in June 2017, and foredune morphology changes were measured using unmanned aerial vehicle photogrammetry following a storm in September 2023. Significant erosion was driven by intense wave energy over multiple spring tide cycles, resulting in northward sand movement. Climate change is rejected as a cause of the erosion based on optically stimulated luminescence dates that show some of the eroded sediments to be approximately 8 900 years old. Instead, the cause is thought to be the interruption of long-term sand supply. Long-term sand dynamics are seldom considered in coastal erosion vulnerability assessments, and sediment age may be a novel factor in understanding this dynamic.