Dynamics of Land Cover and Impact on Stream flow in the Modder River Basin of South Africa: Case Study of a Quaternary Catchment

Abstract

Understanding how dynamics in individual land use types influence changes in streamflow is vital. Most hydrological studies are based on paired catchment and modelling approaches. These are data intensive and require a long period of monitoring. To determine the hydrological effects of tropical vegetation conversion over large areas, it is manageable to study the same basin over different time periods. The study analysed changes in historical stream flow patterns with reference to dynamics in land cover in C52A quaternary catchment of South Africa. Landsat images for years 1993, 2004 and 2013 were used for the development of land cover maps. Subsequently, step-change (median point change, Mann-Whitney and Kruskall Willis) and trend detection tests (Spearman’s rho and Kindall’s tau) were applied to average annual discharge and rainfall data for the catchment between 1984 and 2013.Tukey’s honestly significant difference (HSD) test was also used to compare the means. Results revealed that huge land cover changes coincided with significant (p<0.05) changes in streamflow although rainfall remained homogenous over the same period. This suggests that land cover change is intricately coupled to increases in streamflow. In addition, increased runoff is usually accompanied by increased rates of erosion and siltation. To ensure sustainable management of the catchment, therefore, soil and water conservation measures are critical within the broader context of integrated water resources management.