An Improved Methodology for Erosion Hazard Mapping Part I: The Technique

Abstract

The assessment of soil erosion hazard over large areas is an important aid to land evaluation and land use panning. A methodology using a simple factorial scoring procedure for erosion hazard was derived in Zimbabwe in the early 1970s. Recent developments in soil toss prediction models opens the way for improvements in methodologies for the production of erosion hazard maps.

Basing the new procedure on African conditions, limited data availability and coverage at a sub-continental scale, the SLEMSA (Soil Loss Estimation Model for Southern Africa) framework is shown as a useful tool in designing a suitable methodology. Through the major factors in erosion—relief, rainfall, vegetation and soil—variables are derived for the measurement of their influence on erosion. The abstraction of the variables—average slope, kinetic energy of rainfall, vegetal cover and an index of erodibility—is described and it is shown how they can be combined through a set of design graphs taken from the Zimbabwe Highveld version of the SLEMSA framework. Hazard is expressed in ‘Erosion Hazard Units’ and not tonnes per hectare.