Gully erosion is an environmental problem that has over decades threatened Anambra State as well as other parts of Nigeria and countries of sub-Saharan Africa. Gullies threaten the soil, water, material resources and agricultural productivity and cause human losses annually. It accounts for the severe environmental degradation in Anambra State and the South-East of Nigeria arising from heavy runoff and soil loss. Conventional Soil Loss Equations/Models, used for calculating annual soil loss to aid predictions of soil vulnerability to erosion, encapsulate the erodibility factor (a soil parameter) which constitutes some difficulty in prediction processes. The associated problem is hinged on the fact that erodibility is relatively difficult to measure and its evaluation in any soil erosion prediction modeling requires some rigorous process that is prone to error. In our new geophysically modified Soil Loss Equation, the ‘erodibility factor’ has thus been replaced with the ‘rigidity factor’ (a geophysical parameter) due to its error-free and relative ease of measurement and acquisition. We have used the power law modeling approach to fit the rigidity modulus with other input variables in order to obtain the new geophysical soil loss prediction model. Inputting rigidity into our newly modified soil loss equation, however, requires introduction of a constant λ which eliminates any dimensional problem in the model. We have called this ‘the area constant’ and it is uniquely characteristic of any given geographic or geologic area under investigation. The rigidity data used in testing our model were calculated from existing Vp and Vs values derived from previous works documented in the literature. For the Anambra Basin which constitutes our study area, we obtained the value of λ as 2.438 x1012 t2ha-1hr-1MJ-1. Use of this λ-value in conjunction with the rigidity data and other values in our new equation gave soil loss rates in the range of 0.013 - 0.067 tha-1yr-1, showing only slight erosion in the study area. We do not claim to have exhausted this approach. However, we have in this study successfully derived a new geophysical soil loss model suitable for erosion prediction, monitoring and control in any part of the world.

Keywords: Prediction, monitoring, geophysical, modified, soil, loss, model