The geomorphic provinces of South Africa, Lesotho and Swaziland: A physiographic subdivision for earth and environmental scientists

Abstract

This work has drawn upon previous attempts to define geomorphic provinces, but also on more recent work on the geological and geomorphological evolution of southern African fluvial systems. It has also used Digital Terrain Model (DTM)-derived data and statistical techniques to determine 34 geomorphic provinces and 12 sub-provinces within SouthAfrica, Lesotho and Swaziland. Ninety-nine main stem river longitudinal profiles and valley cross-sectional profiles were generated from the DTM-derived data, and a statistical technique, the Worsley likelihood ratio test (WLRT), was applied to define statistically significant changes in slope and valley cross-sectional width along the river continuum. This isolated 471 macro-reaches for the 99 main stem rivers. Each macro-reach was then analysed using a variety of descriptors including shape, best fit curve, slope, sediment storage potential and valley width. Principal component analysis was applied to the data set to determine whether significant groupings existed, indicating significant similarities in the data by way of area, and conversely, whether distinct differences between groups of data were evident. The scores for the whole data set showed a large grouping around the origin with some scatter along the PC1 axis. Distinct groups were, however, evident for macro-reaches within each province. These reflect the extent of uniformity in the slopes, valley widths, altitudes and shape descriptors of each province. A description of each of the 34 provinces and 12 sub-provinces is presented.