Abstract
Floods in Ghana have become a perennial challenge in the major cities and communities located in low-lying areas. Therefore, cities and communities located in these areas have been classified as potential or natural flood-prone zones. In this study, the Digital Elevation Model (DEM) of the Accra Metropolis was used to assess the drainage density and elevation patterns of the area. The annual population estimation data and flood damages were assessed to understand the damages and population trend. This research focused primarily on the elevation patterns, slope patterns, and drainage density of the Accra Metropolis. Very high drainage density values, which range between 149 and 1117 m/m2, showed very high runoff converging areas. High drainage density was also found to be in the range of 1117–1702 m/m2, which defined the area as a high runoff converging point. The medium and low converging points of runoff were also found to be ranging between 1702–2563 m/m2 and 2563–4070 m/m2, respectively. About 32% of the study area is covered by natural flood-prone zones, whereas flood-prone zones also covered 33% and frequent flood zones represent 25%. Areas in the Accra Metropolis that fall in the Accraian and Togo series rock types experience high floods. However, the lineament networks (geological structures) that dominate the Dahomeyan series imply that the geological structures in the Dahomeyan series also channel the runoffs into the low-lying areas, thereby contributing to the perennial flooding in the Accra Metropolis.
Highlights
The immense expansion of many cities in Ghana without strict adherence to developmental regulations has made cities vulnerable to a range of natural disasters
Frequent flood-prone zones represent areas that will often experience floods due to the expansion of the city. Floodprone areas are those areas within the catchment that are susceptible to floods due to the connection of these areas with natural flood-prone areas as well as city rebranding
High drainage density was found to be in the range of 1117–1702 m/ m2, which defined the area as a high runoff converging point
Summary
The immense expansion of many cities in Ghana without strict adherence to developmental regulations has made cities vulnerable to a range of natural disasters. Floods in Ghana have become a perennial challenge in the major cities and communities located in low-lying areas. Lowlying areas have been found to be liable to flooding (Attipoe 2014). Cities and communities located in these low-lying areas can be classified as potential flood-prone areas. Infrastructural developments have encroached on these areas; that is building on waterways and paving of surface areas prevent infiltration of precipitation into the soil (Okyere et al 2013). Areas (swamps and valleys) meant for the detention of runoffs have been used for infrastructural developments, which eventually contribute to flooding. These areas were naturally designated for detaining excessive runoff and overland flows, which help to cut down the time of concentration of surface runoffs
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