River sediment discharge influence on short-term shoreline change of Anlo beach, Western Region, Ghana

Abstract

Riverine systems are important due to sediment transport to the coast. However, this benefit is decreasing due to increasing rate of human influences that affect river flow pattern and sediment discharge to coastal areas, leading to coastal instability in many countries. This study assessed riverine sediment discharge contributions to the short-term evolution of the coastline of the Anlo Beach in Ghana. The Pra River catchment with focus on the coastal frontage (~3.5 km) and 1.6 km inland was studied, with field surveys for six months (May to October, 2022). River depths, sediment load, river velocities, and aerials photographs were collected for each survey, and subsequently processed and analysed with established protocols in ArcMap to produce shoreline changes, bathymetry maps, river sediment and water discharges and particle size distribution. Results from the study suggest a decreasing trend of average daily river discharges, sediment load and particle sizes. These results were however larger than what was reported in other rivers in and outside Ghana. Beach sediment and shoreline are also eroding at a rate of -105,695.72 m3 and -8.22 m for the six months period. The dynamics of the beach is associated with illegal small-scale mining that supplies smaller sediment particles to the beach, and reduction in longshore sediment transport by sea defence structures located to the west of this beach. Also, shallow bathymetry was observed at the Pra Estuary, which could lead to flooding during rainfall and high discharges.