ABSTRACT
With the aim to better understand the key hydrological processes and runoff generation mechanisms in the semi-arid meso-scale Kaap catchment in South Africa, a hydrological model was developed using the open source STREAM model. Dominant runoff processes were mapped using a simplified Height Above the Nearest Drainage (HAND) approach combined with geology. Furthermore, the model was informed by process studies (hydrograph separation using tracers and digital filters) to enhance understanding on runoff processes in the Kaap. The Prediction in Ungauged Basins (PUB) framework of runoff signatures was used to analyse the model results. The results showed distinct patterns of flow generation in the Noordkaap and Suidkaap catchments, versus the Queens and Kaap. Furthermore, the high impact of water abstractions and evaporation during the dry season was highlighted, affecting low flows in the catchment. Results also indicate that the root zone storage and the parameters of effective rainfall separation (between unsaturated and saturated zone), quickflow coefficient and capillary rise, were very sensitive in the model. The inclusion of capillary rise (feedback from saturated to unsaturated zone) greatly improved simulation results, which suggests greater surface-groundwater interactions, particularly in the Queens and Kaap catchments.
