Trends in soil erosion and land use in the Upper Tugela catchment

Abstract

Each year, approximately 75 billion tons of soil are eroded from the Earth’s terrestrial ecosystems and the majority of agricultural land in the world is losing soil at rates of between 13 tons/ha/year and 40 tons/ha/year. South Africa is prone to soil erosion, because of poor farming methods, together with soils which are erodible. In order to understand more about the nature of soil erosion in South Africa, the geology and lithology needs to be well understood too. This study adds to the understanding of the relationship between soil erosion and land use. In South Africa soil erosion research has been undertaken, however, each and every region requires its own research on a different scale and using different technique to fit the unique characteristics of the area. This research begins by investigating the studies which have been undertaken concerning soil erosion and land use, and how these processes are defined and expressed in different contexts. An historical analysis of the former Homeland areas, recreational resorts and Royal Natal National Park in the upper Tugela catchment was conducted over a 50-year period (1964 to 2014). Field trips were conducted in six study sites, in the Bergville district, Drakensberg, to carry out ground-truthing, obtain onsite imagery and validate/verify findings from the research. Desktop research entailed the use of ArcGIS, Google Earth, statistics and an analysis of aerial images which date from 1964 to 2014. The results show a greater number of erosion features and more extensive erosion in the former Homeland areas, which form part of the rural area of the study site, compared to the Park (Royal Natal National Park) and recreational resorts. Erosion in the study sites was defined according to the SARCCUS framework, and this involves the development from primarily sheet erosion in 1964, to intricate gully patterns and river bank erosion in 2014. The study also shows that there is a relationship between population and the vegetated area: as the number of households increased from 1964 to 2014, the grass cover, trees and grazing land in the area declined. Overgrazing plays a role in determining the extent of the erosion. However, it is the relationship between increasing population numbers and the nature of livestock keeping among village dwellers which influenced overgrazing levels, and subsequently the extent of erosion. Mitigating soil erosion impacts is an issue which has to be addressed not only on the local scale, but national government also needs to make it a point that the general landscape of the country is well managed with regards to soil erosion. The outcomes from this study support the notion that soil erosion processes are very complex and that delineation of soil erosion features entails a certain level of subjectivity. Human influences and land use dynamics also influence the rates of soil erosion and this study shows how different land uses, but similar environmental factors, can lead to different rates and intensities of soil erosion. In conjunction with GIS and remote sensing, satellite imagery and aerial photos play an important role in the analysis and understanding of the study area and the different geological, biological and anthropological features present. The presence and the availability of high quality imagery helps then in ensuring that resolute and reliable information is established.