Abstract:
Gully erosion is a degradation process affecting soils in many parts of theWorld. Despite the complexity of a series of collective factors across
different spatial scales, previous research has not yet explicitly quantified factor dominance between different sized gullies. This factorial
analysis quantifies the differences in factor dominance between continuous gullies (cgs) and discontinuous gullies (dgs). First, gullies (totaling
5273 ha) visible from SPOT 5 imagery were mapped for a catchment (nearly 5000 km2) located in the Eastern Cape Province of South Africa.
Eleven important factors were integrated into a geographical information system including topographical variables, parent material-soil
associations and land use–cover interactions. These were utilized in a zonal approach in order to determine the extent factors differ between
cgs and dgs. Factors leading to the development of cgs are gentle footslopes in zones of saturation along drainage paths with a large
contributing area, erodible duplex soils derived from mudstones and poor vegetation cover due to overgrazing. Compared to cgs conditions,
more dgs occur on rolling slopes where the surface becomes less frequently saturated with a smaller contributing area, soils are more stable
and shallow. Factorial analysis further illustrates that differences in factor dominance between the two groups of gullies is most apparent for
soil factors. A combination of overgrazing and susceptible mudstones proves to be key factors that consistently determine the development of
cgs and dgs.
