A RUNOFF CAPABILITY CLASSIFICATION-SYSTEM BASED ON SURFACE-FEATURES CRITERIA IN SEMIARID AREAS OF WEST AFRICA

An analysis of the factors influencing infiltration and runoff was carried out using data obtained under simulated rainfall conditions on 87 plots in arid and semi-arid areas of West Africa, arranged in a hierarchical sequence. One of the key factors to emerge from this typological classification is the type of surface crust. Together with faunal activity, vegetation cover and surface roughness, this parameter permits the inclusion of a 'unit surface' factor in the classification system. Each unit surface is characterized in terms of genetic, morphological and hydrological properties. At a higher level, the combination of these unit surfaces allows a soil surface features unit' to be defined, based on an original mapping method. The samples, once defined in this system, were found to correspond to homogeneous criteria both in terms of evolution dynamics and hydrological behaviour. Furthermore, such cartography could be successfully extrapolated through remote sensing image analysis, making possible a classification of the runoff capability of small watersheds based on objective and standardized criteria.