Investigation and modelling of base flow and salt loads into inland rivers of New South Wales

Rising stream salinity is a major threat to rivers in the Murray-Darling Basin. Hence, the management of river salinity forms a major component of the NSW State Salinity Strategy (SSS) and the Murray-Darling Basin Ministerial Council (MDBMC) Basin Salinity Management Strategy(BSMS). The Department of Infrastructure, Planning and Natural Resources (DIPNR) has developed a model, the Integrated Quantity Quality Model (IQQM), which can be applied to any river system to investigate the river salinity response to time varying salt load inputs. Management options such as changing flow regimes in regulated rivers and land use change interventions can be investigated with IQQM to evaluate impacts on end of valley salinity targets. In this study, groundwater levels, stream flows and stream water quality data from the Namoi Valley and the Box Creek catchments of NSW were analysed and modelled. Results of modelling stream-aquifer interaction in the Namoi River and groundwater salt inflow in Box Creek identified that two of the most crucial issues of concern were the estimate of surface wash-off salinity and groundwater levels especially close to the streams which affect the groundwater salt inflow. This indicated a need to better consider stream-aquifer interaction within IQQM as well as to understand and quantify salt buildup washoff processes.