Rates and controls of footpath erosion in Giant's Castle Game Reserve, KwaZulu / Natal Drakensberg.

Abstract

The Drakensberg is an important ecological and recreational resource area within southern Africa, yet little knowledge exists concerning the factors controlling soil erosion in the region. The two most important anthropogenic modifiers of natural erosion processes in the areas beyond the: Drakensberg Park main camps and access roads are vegetation burning and the erosion associated with footpaths. This dissertation investigates the rates and controls of footpath erosion in Giant's Castle Game Reserve in the KwaZulu/Natal Drakensberg. Two measurement techniques are employed. Sediment yield and runoff were monitored from six runoff plots installed on different gradients on a high user-intensity footpath. Runoff is found to increase linearly with increasing footpath gradient. Sediment yield increases gradually with increasing footpath gradient to a threshold path gradient of 13.36°, after which sediment yield increases rapidly. Soil eroded from the runoff plots has a finer particle size distribution than the footpath tread surfaces within the plots. Rates of sediment generated from the runoff plots is dependant on the rainfall intensity index (I60), as opposed to rainfall kinetic energy or total rainfall related indices, while runoff is dependant on the El60 index. A 100m point-based survey of footpath attributes, totalling a distance of21km along four paths in the Reserve was undertaken. Where footpath gradients are low and user-intensity is high, path morphometry is dependant on orientation to the slope. Morphology of footpaths with both higher gradients and user-intensities show a dependence on path gradient. The degree of compaction of the footpath tread decreases away from the main camp and is positively related to user-intensity. Multiple path development is. associated with the path width to maximum depth ratios and a threshold ratio range of 4. 0 I to 4. 50 is established for the initiation of secondary path routes. A comparison of the survey data with a survey conducted in 1989 indicate erosion rates between 3.24 and 13. 0 tons/km/a over a four year period. Erosion rates for the runoff plots and for the surveys indicate that the values obtained for the two techniques of measurement utilised in the study approximate each other. Path erosion rates, while still presenting a prnblem, are not uncharacteristically high in Giant's Castle. Game Reserve in comparison to the scarce data available on rates of path erosion within and beyond southern Africa.