Application of the SWAT model to assess the impact of land cover and land use on the hydrologic response in the Olifants Catchment

Water availability in Southern Africa is highly variable both in time and space, thereby exposing the region to high risks in its use. This is further compounded by numerous human activities which tend to impact on the quantity and quality of the water resource. With ever increasing demands on the water resource, the need for a better understanding of hydrological systems becomes crucial as it forms the gateway for providing reliable information for its management. That understanding includes, among others, land and water linkages because land use decisions are water use decisions. Operational hydrology not only provides longterm prediction of human activities on the partitioning of rainfall into catchment flows, but allows for a more holistic management approach to land and water resources. This paper discusses the application of the SWAT model to the B72A, E, F, G & H quaternary catchments in the Olifants Water Management Area of South Africa in assessing the impact of human-environment interactions on streamflow. A sensitivity analysis is performed to identify the driving parameters for the hydrology. The analysis shows that modelling at small spatial scales is indeed more representative as different areas of the watershed respond differently to different parameter changes. Results show an expected correlation between land cover and the hydrologic response with an increase in land cover corresponding to streamflow reduction. Range grass reduces streamflow the most, followed by forestry but arid land gives the highest increase in streamflow. Best model parameter values for the B72E – H catchment were applied in the ungauged B72A quaternary (pilot) catchment with similar biophysical properties, and a MAR of 68mm was obtained which is about 20% less than the virgin streamflow obtained in another study.