Erosion risk mapping of Anambra State in southeastern Nigeria: soil loss estimation by RUSLE model and geoinformatics

Soil erosion is a life-threatening hazard ravaging and displacing many communities in Anambra State, Nigeria. Most erosion studies in this region have been based on geological and geotechnical analyses of soils from gullies. In this paper, the soil erosion risk of Anambra State was evaluated using the Revised Universal Soil Loss Equation (RUSLE) and geoinformatics, to estimate the rate of soil loss and identify vulnerable erosion zones. The RUSLE model was based on five erosion factors (rainfall erosivity (R), soil erodibility (K), topography (LS), vegetation cover (C), and anti-erosion practices (P)). The R-factor ranged from 460.51 to 582.08 MJ/mm/ha(-1) h(-1) year(-1) whereas the K-factor ranged from 0.100 to 0.310 t/h/MJ(-1)/mm(-1). Low-moderate LS-factor values dominated the northern and western portions of the State. However, moderate-high LS-factor scores dominated the eastern and southern portions. The C-factor varied from 0 (in areas covered by water bodies) to 1 (for barren lands). The P-factor ranged from 0.5-1. These five factors were integrated to generate soil loss rates across Anambra. The average annual soil loss ranged from 0 to over 6 t/ha(-1) year(-1). The soil loss results showed that about 5% (242.2 km(2)), 25% (1211 km(2)), 30% (1453.2 km(2)), and 40% (1937.6 km(2)) of the total area have very low, low, medium, and high erosion risks, respectively. The northern and western portions of the State were characterized by very low, low, and moderate soil loss. However, the eastern and southern portions were characterized by high soil loss rate. It was indicated that LS, K, and R are the most important soil loss factors in Anambra.