Monitoring sea level rise-induced hazards along the coast of Accra in Ghana

Abstract

Sea level rise, increased erosion and flooding threaten vulnerable coastal communities globally. Monitoring the changes in the coastal zone enables the risk levels to be detected and quantified. Such information facilitates developing sustainable policies to effectively manage hazards in the coastal zone. This study used available geospatial data to assess the physical state of the Accra coast and established ground control points that will facilitate effective monitoring of change. The data used included a bathymetric map (hard copy) with last revision in 1992, digital topographic map (2002) of the coast, 2005 orthophoto map and the geology map of Accra. The reliability of the data was determined, and the data were analysed using GIS tool. Ten concrete ground control points were established, mapped using DGPS and connected to the Ghana national coordinate system to form a network for effective monitoring in the coastal zone. The results revealed that the western region of the Accra coast has lower elevations onshore which will facilitate inundation from sea level rise. Comparing nearshore bathymetric profiles indicates that the eastern coast is deeper relative to the central and western. This will enable waves to break closer to the coast under increasing sea level rise thereby dissipating energy to facilitate sediment transport. Computed potential sediment transport rate revealed that the rate ranges between 4.1 × 105 and 7.2 × 105 m3/year. Using the control points established as reference points to monitor the coastal system will enable changes that can result in hazard to be detected and quantified.