Flood Risk Zoning of Ghana: Accra Experience

Accra has been experiencing periodic flooding that affect properties and lives. The government seeing the dangers involved, commissioned institutions such as Ministry of Works and Housing, Town and Country Planning and City Engineers to identify such areas and adapt measures that will help reduce the effect of the periodic event. These institutions identify flood risk zones using conventional methods such as watermarks on buildings and reported cases in the news media. Works carried out by these agencies were not able to give details about potential areas that are likely to experience this extreme event. Hence there was the need to find a new method of identifying and mapping of potential flood risk zones. To determine flood risk zones in Accra and its environs a hydrological model (modified rational model) was integrated into the GIS platform, by the arithmetic overlay operation method, using operators such as addition and division. The results show that the delineated areas however experience same rainfall intensity of 140.2 mm yet the flood intensities of these areas differ. For instance, the high flood risk zone covers 35.66 percent of the study area, whiles the low risk zone covers 26.85 percent. And the potential areas likely to experience periodic floods with a given input of rainfall are mostly below the 350-meter contour.