Hydrogeomorphological analysis of Niger River Sub-basins for flood prediction in Anambra State, Nigeria

Abstract

Climate change is associated with heavy and excessive rainfalls in the tropics with anticipated fluvial and pluvial flooding. This study aimed to analyze the natural predispositions of river basins in Anambra State, Nigeria to flooding in this era of changing rainfall characteristics necessitated by climate change. This study used primary and secondary data sources. The primary data include field visits and observations, oral interviews, photographs, and measurements, whereas the secondary data include satellite images from the USGS (SRTM DEM), shapefile from Diva GIS, and other related literature. The morphometric parameters analyzed included the area of the sub-basin, perimeter of the sub-basin, stream order, stream length, stream numbers, and sub-basin length, the drainage density, drainage texture, form factor, shape factor, elongation ratio, relief ratio, relative ratio, ruggedness number, and bifurcation ratio. The findings revealed that the sub-basins are elongated in shape, with a dendritic stream pattern, whereas the other hydrogeomorphological characteristics revealed the flooding propensity and erosivity level downstream of their basins. The drainage density (D_d) of the sub-basins of Anambra state indicates that the basins are made up of porous subsurface material and, therefore, will not encourage flooding. The drainage texture (D_t) has a very coarse texture category and indicates the presence of fewer streams over basins, as it considers the total number of streams of all orders. The form factor (R_f) indicates that there is a very low possibility of sudden peak discharge in the basins during heavy rainfalls. The shape factor (S_f) indicates strongly elongated basins (i.e., S_f > 0.45) elongated basins indicate a long travel time for flow from the headwaters to the outlets. The sub-basins’ terrain are categorized as having slight, moderate, and sharp morphology with slight, moderate, and sharp roughness and unevenness; slight to moderate exposure to the risks of flood hazards; moderate soil erosion; and/or mass movement. This implies that the increase in flooding in the state might be attributed to increasing urbanization, dense settlement, and human intervention in river flow.