Soil Properties Controlling Gully Erosion in the Maphutseng Valley, Lesotho

G. van Zijl, F. Ellis and A. Rozanov

This project is based in the Maphutseng valley of Lesotho, near the town of Mohale’s hoek, in the west of the country. This valley is on the boundary between the highlands and the lowlands, where most of the crop production is concentrated. Food security in the area is jeopardized by wide-spread soil erosion manifested as gullies and loss of topsoil from agricultural land.

The objective of the study is to find reasons why different areas in the same sub-catchment experienced different rates of soil erosion, and to find an easily identifiable soil characteristic which will point to unstable soils, to assist extension officers and farmers in the area.

In the sub-catchment chosen for the study, a donga runs from the top of Thaba Linoha (+-2100m above sea level), through four different geological formations into the Maphutseng river (+-1450m above sea level) approximately 4 km away. On the eastern side of the donga the soil seems to be stable, while the western side is characterised by a maze of branching dongas. These branches formed some 40 years ago over a period of 10 - 15 years on cultivated land.

The factors which influence soil erosion, i.e. soil, climate, slope and land management practices are considered using repeat aerial photography in a GIS environment. Drainage pathways are mapped with a DEM. Soil samples from the areas of different channel density are analyzed to conclude which soil properties most influence the occurrence of dongas.

MSc Student: G. Van Zijl

Funding: Private