A Study of the Dynamics of Soil Erosion Using Rusle2 Modelling and Geospatial Tool in Edda-Afikpo Mesas, South Eastern Nigeria

Abstract

Abstract The Revised Universal Soil Loss Equation (RUSLE) was used to study the soil erosion processes in Edda-Afikpo mesas, Lower Cross River watersheds,Nigeria. The mesas occupy an area estimated at 60km2 on a surface relief of about 284m. DEM data, satellite images and basemap of the area were used. Remotely sensed data were ground-truthed through extensive field works. The results show that the process is facilitated by the Trifecta of hill slope hydrology, geology and land use practices. Steep hill Slope of values 78 % at the major hot spots, very fragile, dry and non-plastic sandy soils all aid sediment detachment. Analysis of the index properties which include Liquid Limit(LL) of 25-30,moisture content(w%) of 5.9-7.4,permeability of 1.541x10-3 – 1.636x10-3 cm/s and shear strength of 36-42 KN/m2 predispose the sediments to detachment and erosion. Based on the analysis, the amount of soil loss in the project area is about 1373.79 ton per year. Soil erosivity factor is high at the mesas(5023.83 MJ mm ha−1 h−1 yr−1 - 5069.51 MJ mm ha−1 h−1 yr−1) The sandy layer attain thickness of 50m-60m in places and with high pore pressure development, slope failure are triggered during intense storm events. In terms of vulnerability level in erosion risk, high to very high constitute 4.1% of the watershed which translate to 5.05km2 of the 59km2. The various processes occur simultaneously and are exacerbated by human factors through seasonal bush burning and development along drainage lines. The study reveals that 18.8% of the available land for development is at high to very high risk of erosion. The soil loss model has been validated and the hotspots from the map coincide with the gully sites. The results of this research can therefore be used for conservation and adaptation purposes.