Assessment of recession flow variability and the surficial lithology impact : a case study of Buffalo River catchment, Eastern Cape, South Africa.

Abstract

The recession identity is an essential indicator of river performance, health and diminution status. This study, therefore, presents an assessment of streamflow recession characteristics in relation to the hydrostratigraphy property of watershed. The streamflow recession assessment was carried out by computing the flow duration curve (FDC) and baseflow index (BFI) analyses of 28 year streamflow records at six distinct streamflow gauging stations. Digital processed aeromagnetic map was hybridized with geological survey and map review for the construction and characterization of concise watershed surficial lithology. The FDC plot of low-flow slopes and Q95 reported the flow per station as thus; Buffalo (− 0.0113; 0.0026), Tshoxa (− 0.0029, 0.0016), Yellowwoods (− 0.0022, 0.0008), Mgqakwebe (− 0.0017, 0.0007), Quencwe (− 0.0009, 0.0002), and Ngqokweni (− 0.0005, 0.0001). Similarly, BFI results show the following rank: Buffalo (0.541), Yellowwoods (0.488), Tshoxa (0.450), Mgqakwebe (0.443), Quencwe (0.415), and Ngqokweni (0.332). The recession analysis revealed that the Q95 slope of the stochastic FDC approach is a more reliable recession estimate for environmental flow. The assessment of the recession–lithology relationship suggests that the porosity network of the contact zone and fracture system of dolerite may produce a weightier impact of baseflow discharge in support of environmental flow over the hydraulic conductivity of sandstone. The physiographic trends of streamflow response suggest the influence of the high relief on streamflow flux. The overall results suggest that the hybrid approach of FDC and BFI analyses are highly effective for replicating the streamflow recession at the catchment stage and could be adopted for investigation of river sustainability.