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. The continuous decline in water quality in many regions is forcing a shiftfrom quantity-based water resources management to a greater emphasis onwater quality management. Water quality models can act as invaluable toolsas they facilitate a conceptual understanding of processes affecting waterquality and can be used to investigate the water quality consequences ofmanagement scenarios. In South Africa, the Water Quality Systems AssessmentModel (WQSAM) was developed as a management-focussed water quality modelthat is relatively simple to be able to utilise the small amount ofavailable observed data. Importantly, WQSAM explicitly links to systems(yield) models routinely used in water resources management in South Africaby using their flow output to drive water quality simulations. AlthoughWQSAM has been shown to be able to represent the variability of waterquality in South African rivers, its focus on management from a SouthAfrican perspective limits its use to within southern African regions forwhich specific systems model setups exist. Facilitating the use of WQSAMwithin catchments outside of southern Africa and within catchments for whichthese systems model setups to not exist would require WQSAM to be able tolink to a simple-to-use and internationally-applied systems model. One suchsystems model is the Water Evaluation and Planning (WEAP) model, whichincorporates a rainfall-runoff component (natural hydrology), and reservoirstorage, return flows and abstractions (systems modelling), but within whichwater quality modelling facilities are rudimentary. The aims of the currentstudy were therefore to: (1) adapt the WQSAM model to be able to use as inputthe flow outputs of the WEAP model and; (2) provide an initial assessment ofhow successful this linkage was by application of the WEAP and WQSAM modelsto the Buffalo River for historical conditions; a small, semi-arid andimpacted catchment in the Eastern Cape of South Africa. The simulations ofthe two models were compared to the available observed data, with theinitial focus within WQSAM on a simulation of instream total dissolvedsolids (TDS) and nutrient concentrations. The WEAP model was able toadequately simulate flow in the Buffalo River catchment, with considerationof human inputs and outputs. WQSAM was adapted to successfully take as inputthe flow output of the WEAP model, and the simulations of nutrients by WQSAMprovided a good representation of the variability of observed nutrientconcentrations in the catchment. This study showed that the WQSAM model isable to accept flow inputs from the WEAP model, and that this approach isable to provide satisfactory estimates of both flow and water quality for asmall, semi-arid and impacted catchment. It is hoped that this research willencourage the application of WQSAM to an increased number of catchmentswithin southern Africa and beyond.

Water quality modelling of an impacted semi-arid catchment using flow data from the WEAP model