The development of a new methodology to interpret run of river salinity data to assess salt inflow to the River Murray

In addition to the threat posed by high salinity to drinking water, increased salinity in the River Murray also represents a threat to the health of floodplains, wetlands and may increase the costs of infrastructure maintenance. In the Lower Murray Basin most of the salts in the river originate from groundwater. Run of river salinity surveys are used to measure salt inflow. They measure electrical conductivity every kilometre over five consecutive days, at low and steady river flows. For a robust interpretation of salt inflow, the background electrical conductivity has to be removed from the measurements. The existing methodology is robust for analysing cumulative salt inflows over river reaches but assigns salt inflows up to several kilometres downstream from where they actually occur. A new method has therefore been developed to assign the salt inflow more closely to the location where it actually occurs and at the correct rate. The new methodology is based on the assumptions that salt inflow is the function of space only (during the survey) and the background conductivity can be described by the temporal variations observed at a fixed location. These in turn allow better targeting of the high salt inflow zones for salt interception.