Flood risk assessment and reduction in the Ankobra estuary of the Western Region of Ghana

Abstract

Floods are common phenomena within the Ankobra estuary. However, the unavailability of records on the nature of floods, exposure of communities to floods and a flood risk map tend to limit effective flood risk control and management within the estuary. This study therefore sought to assess flood risk within the Ankobra estuary and examine how geodesign can be used as a flood risk reduction strategy within the plan. The research techniques employed in the study include interviews, community mapping, observation, measurements (tape) and geographic information systems techniques (onscreen digitising, global positioning system mapping, spatial multi-criteria evaluation and geodesign). Results from the study indicate that the estuary experiences three types of flood (riverine, coastal and urban). Risk levels derived ranged from extreme, 0.75 – 1; high, 0.5 – 0.74; medium 0.25 – 0.49 to low, 0 – 0.24. The extreme risk zone covered an area of 46,725m2; high risk zone covered 701,525m2; moderate risk zone, 248,150m2 and low risk zone, 9,167,758m2. Geodesign simulations (change of height foundation of buildings and remodelled landscape including drainage system) were undertaken. They produced more desirable result than the original risk levels. It was recommended that persons within high risk zones after the geodesign simulations should be relocated to low risk zones.