A GIS based flood risk mapping along the Niger-Benue river basin in Nigeria using watershed approach

Floods are water induced disasters that lead to temporary inundation of dry land and cause serious damages in the affected location such as loss of lives and properties and destruction of infrastructures. They have become common occurrences in every part Nigeria and the recorded impacts of flooding on the inhabitants are alarming, causing hundreds of deaths and rendering thousands homeless. The impact of floods on people globally has led to the development of mitigation measures that could reduce the associated risk of floods to a manageable point. The management of flood risk begins with identification of areas prone to flood. This study used the scientific technique of GIS to identify flood risk areas along the River Niger-Benue basin. Satellite imageries SRTM DEM that covers the study area was used in this research. Monthly rainfall data was used to generate maps of standardized precipitation index (SPI) for thirty years (1978 to 2007). The SPI maps were used to determine the degree of precipitation condition across Nigeria and also to identify the locations where flood events are being triggered. The SRTM DEM was used to generate the flow direction and flow accumulation maps. Flow direction and Flow accumulation were used to generate the watershed and flood risk map. The flood risk map shows that 45% of Nigeria towns and villages are within the flood risk zone. Finally, some recommendations were made which will help the policy makers improve on flood management in the country.Key Words: Flood, Flood risk, Flow direction, Satellite imager