GIS-based estimation of soil erosion rates and identification of critical areas in Anambra sub-basin, Nigeria

Estimation of soil loss through water erosion is an essential exercise which can help decision makers and planners determine the severity of soil loss through rill and sheet erosion and also curtail the development of further gullies in an area already ravaged by gully erosion. While Universal Soil Loss Equation (USLE) is the most commonly adopted model because it provides a straight forward approach for qualitative estimation of soil loss, however its rainfall erosivity component is found incompetent in most parts of the world. To overcome this deficiency, the Revised Universal Soil Loss Equation (RUSLE) was implemented using rainfall erosivity (R) values peculiar to tropical environment of the Anambra area of Nigeria. Rainfall erosivity (R-factor), soil erodibility (K-factor), slope factor (LS-factor), and cover management (C-factor) were generated in GIS environment and then integrated based on RUSLE equation to estimate the rate of soil erosion. The study indicated that about 1804.39 km(2) (39.49 %) of the study area have slight erosion rate of 0-10 t ha(-1) year(-1), while the rates of erosion in 746.60 km(2) (16.34 %), 1025.38 km(2) (22.44 %), 659.55 km(2) (14.43 %), 287.08 km(2) (6.28 %), and 46.59 km(2) (1.02 %) of the study area are 10.6-85.3, 85.4-235.2, 235.3-608, 608.1-2200 and >2200.1 t ha(-1) year(-1) respectively. The study revealed that high rainfall erosivity combined with moderate to high slope factor and decreasing vegetal cover are the major factors driving soil loss in the area.