Measuring and Simulating Shoreline Morphodynamics in the Volta Delta, Ghana

Abstract

Coastal erosion is a major challenge facing coastal regions globally. It is projected to increase on regional to global scale as sea levels continue to rise. To manage the situation sustainably, coastal managers require relevant scientific information such as beach sediment and shoreline dynamics. Shoreline change measurement and simulation especially at local scale and at higher resolutions are relevant for decision making and engineering. A review of literature has brought to the fore that the Volta delta is a hotspot for coastal erosion; however, mainly low resolution remotely sensed imagery has been used to assess changes in the Volta delta of Ghana, which compromises the accuracy of the information. In this study, different sets of high-resolution datasets from Unmanned Aerial Vehicles (UAV) surveys and satellite imagery, as well as numerical modelling using Littoral Processes FM (Flexible Mesh) are adapted to estimate historical beach sediment and shoreline dynamics and predict future evolution under sea level rise up to the mid-century. The results show a net loss of beach sediment on the western side of the Volta Delta up to 9,000m3 whilst the eastern side experienced net gain up to 12,100 m3 in the short term. Relatively, short-term erosion rates were higher compared to the medium term shoreline erosion. Simulation of future conditions indicates an increase in shoreline erosion rates by 4 cm/y by mid-century with sea level rise of 13 cm at Old Ningo. Consequently, the shoreline will recede up to 70m inland, which will negatively influence livelihoods and aesthetic value of the area. The study recommends soft engineering approach such as sediment beach nourishment or the Dutch ‘sand motor’ system to protect the shoreline and the community. Regulations should also be enforced to halt nearshore sand and gravel mining.