Emphasising the soil factor in geomorphological studies of gully erosion: a case study in Maphutseng, Lesotho

Abstract

The severe destruction caused by gully erosion in the Lowlands of Lesotho is well known. In spite of the large number of studies on gully erosion in Lesotho, the problem still persists. To effectively combat soil erosion, erosion specialists need to come up with answers to hard questions. This paper attempts to answer three such questions for a catchment in Maphutseng, Lesotho: why is gullying happening? Can we do anything about it? And is action worthwhile? Soil was included along with geology, land use and slope gradient in a spatial analysis, using aerial photographs from 1957 and 2004, of the severely degraded catchment. Aggregate stability measurements were conducted on the soil associations. Gully extension between 1957 and 2004 in this catchment was controlled by the spatial extent of dispersible duplex soils. The new gullies formed by piping, limiting anti-erosion measures to ones which inhibit the build-up of free water in the subsoil. The position in the erosion cycle indicated where anti-erosion works will have the largest impact. Soil erodibility played a large role in these findings and should be considered when studying gully erosion.