Identification of runoff generation processes using combined hydrometric, tracer and geophysical methods in a headwater catchment in South Africa

Classical hydrometric measurements and detailed 2-D electrical resistivity imaging (ERI) surveys were combined with tracer sampling to identify the hydrological processes in a semi-arid headwater catchment in the Eastern Cape Province of South Africa. The analysis of precipitation and runoff events emphasized the strong link between precipitation and runoff formation characteristics. Soil water tension and groundwater level observations demonstrated the development of a perched water table within the soil layer. These results are supported by tracer-based runoff component separations and illustrate the important role of the shallow subsurface component. The ERI investigation permitted further insight into the structure of the subsurface. Finally, the ERI survey, in combination with time domain reflectometry (TDR) measurements, allowed the extrapolation of selective soil water content measurements. To summarize, the application and combination of different field methods led to the development of a conceptual model of the hydrological functioning of this catchment. The dominant role of the subsurface mechanisms was evaluated.