A hillslope version of the revised Morgan, Morgan and Finney water erosion model

Abstract

The revised Morgan, Morgan and Finney (rMMF) water erosion model calculates annual surface runoff and soil loss from field-sized areas. The original version of the rMMF is neither suited to calculate water erosion along irregular hillslopes, nor capable to allow infiltration of once generated surface runoff at places where the runoff speed slows down, and infiltration could occur under natural conditions. The aim of this article is to describe a new hillslope version of the rMMF model that allows infiltration of surface runoff, and to show examples of soil erosion modelling along real and hypothetical hillslopes. The new hillslope version (hMMF) splits the entire hillslope into a number of sections that have individual properties, such as slope angle, slope length, soil properties and vegetation characteristics. The surface runoff along the slope is calculated by summing the volume of surface runoff generated in a particular section with the surface runoff coming from the immediate upslope section. The related sediment transport is calculated for each section using the calculated detachment for the section, the sediment coming from the upslope section and the transport capacity. A new variable is introduced to account for infiltration of surface runoff and allows simulating the effects of soil and water conservation structures on water erosion. The model was tested using measured data from plots in Africa, Asia, the US and Europe, as well as for a surveyed hillslope in Tunisia (Barbara watershed). Overall, the performance of the hMMF was reasonable for surface runoff and poor for soil loss when recommended input variable values are used. Calibration of the model resulted in a good performance, which shows the capability of the hMMF model to reproduce measured surface runoff and erosion amounts. In addition, realistic water erosion patterns on hillslopes with soil and water conservation can be simulated.