Sediment particle sizes and river discharge implications on shoreline change along Anlo Beach, Ghana

Abstract

Anthropogenic activities within river catchments significantly alter river flow patterns and sediment discharge into coastal zones, impacting coastal systems and their management. To address the persistent erosion of Anlo Beach in Ghana, this study aims to evaluate the role of sediment discharge from the Pra River in shaping the beach's evolution. Specifically, the research seeks to quantify sediment inputs, assess shoreline changes, and identify the factors driving coastal erosion. Using a combination of Landsat 7, 8, 9, and Sentinel-2 satellite imagery over a 10-year period, alongside in situ measurements of flow velocities, sediment load, river bathymetry, and beach aerial photos over six months (May-October, 2022), we analysed shoreline dynamics and sediment characteristics. Satellite data were processed using the CoastSat toolkit, while in situ data were analysed using sediment discharge equations and protocols in ArcMap. Results reveal an average shoreline erosion rate of 5–15 m/year over the past decade, with a sediment loss of approximately 100,000 m³ in the last six months. The sediment transported by the Pra River to Anlo Beach is predominantly very fine-grained, likely due to upstream small-scale mining activities, which reduces effective sediment deposition and exacerbate erosion. The findings underscore an urgent need for targeted management interventions to mitigate coastal erosion and socio-economic impacts on the Anlo Beach community.