A GIS-based assessment of the potential soil erosion and flood hazard zones in Ekiti State, Southwestern Nigeria using integrated RUSLE and HAND models

Abstract

Soil loss estimation and flood hazard mapping cannot be overemphasized due to their environmental, economic and societal concern. Thus, the main objective of this study was to assess the potential soil erosion and flood hazards zones using Revised Universal Soil Loss Equation (RUSLE) and Hand Above Nearest Drainage (HAND) models, respectively for appropriate conservation and prevention measures in Ekiti State, Southwestern Nigeria. The result reveals annual soil erosion ranges from 0 to 889 t ha−1 year−1. The estimated total annual soil loss in the state was around 1.5 million tonnes, of this, 193223.3 tonnes which covers 7508 ha was lost at a rate much greater than the tolerable soil loss rate. Soil erosion vulnerability mapping was done using six (6) categories of soil loss severity from slight to very severe. Soil erosion rates varied from 0.21 t ha−1 year−1 in forests to 1.69 t ha−1 year−1 under bare soils. The very steep slope category had the highest soil erosion rate of 15.07 t ha−1 year−1 while the gentle slope regions had the least soil erosion rate of 0.39 t ha−1 year−1. About 23% of the area which covers 115847.58 ha was prone to high flood hazard whereas 15.69% (80932.30 ha) was moderately susceptible to flood risk. Approximately 15% of the area was susceptible to low flood hazard zone while 44.90% were vulnerable to very low flood occurrence. LULC has significant effect on the spatial pattern of soil loss in the study area. Potential soil loss risk zones were highly related to the degree and inclination of slope. The reported results can serve as preliminary information to determine erosion and flood hotspots in the study area and as input for policy decision for disasters prevention and conservation measures.