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SHUTTLE RADAR TOPOGRAPHIC MISSION (SRTM) ANALYSIS
FOR UNDERSTANDING THE SOUTH AFRICAN LANDSCAPE

As an independent expert, Bruce King has been undertaking this research.

The reason for this research was to determine whether the South African landscape is really as it has been portrayed by various distinguished landform experts, i.e. having the typical profile shown below.

The investigation was undertaken first by recording 27 attributes covering basic landforms, rainfall, local relief, altitude, rock type, land cover, drainage and terrain morphology, at the intersection of every minute of latitude and longitude on 50 randomly selected 1:50,000 scale topographic maps, and secondly by recording the basic landforms and local relief at the intersections of a 122-point grid placed over most of the 1:50,000 scale mapping of South Africa as recorded by the Shuttle Radar Topographic Mission (SRTM).

Contour map (right) produced from SRTM data of the South African Western Escarpment (shown in photograph on the left). Note how the contour spacing increases downslope indicating a concave slope.

The initial investigation demonstrated that the likelihood of the kind of landscape shown above, i.e. an escarpment above a concave 'pediment' slope, is found where the local relief is greater than the value shown by the curve in the graph to the right. It is argued that the reason for this relationship is that sheetwash erosion is more likely where there is scarce vegetation found in more arid climates. Sheetwash is considered to produce concave slopes. Local relief is needed to provide sufficient potential energy. The investigation also demonstrated the drainage density relationship shown below, showing the dense drainage where there is very little vegetation. As the vegetation density increases, the drainage density decreases to a minimum in the 'bushveld' (a savanna biome of grassland with trees); thereafter, as the rainfall increases, the vegetation is insufficient to prevent the increase in drainage density.

The SRTM study showed where the C+E (concave slope + escarpment) landscape dominates as indicated in the picture above; and where there are convex slopes where a C+E landscape would be expected (AXT in the figure below), mainly due to recent episodes of erosion.
ACT indicates a C+E landscape where it would not be expected according to the local relief-rainfall curve.) The investigation showed that the C+E landscape is an old landscape, preserved where more recent erosion episodes have not reached.
For further details, see: King R. B. (2008), South African pediments and interfluves. In Gallagher, K., Jones, S.J. & Wainwright, J. (eds) Landscape Evolution: Denudation, Climate and Tectonics Over Different Time and Space Scales. Geological Society, London, Special Publications, 296, 167-181. http://sp.lyellcollection.org/content/296/1/167.