Change in in-stream salinity from interception of saline groundwater discharge into the Lower River Murray, Australia

Abstract

Salt accessions are the major water quality issue of the rivers and streams of the Murray-Darling Basin. The saline Murray Group Aquifer, the salinity of which exceeds 20,000 muS/cm, discharges an estimated 200 t/d of salt into the River Murray in South Australia between Lock 3 and Holder, 40 km downstream. Salinity mitigation works were needed to sustain irrigated agriculture and to maintain the quality of domestic, industrial and urban water supplies. Forty nine wells were drilled to the aquifer between Lock 3 and Holder from late 1989 to August 1990. Pumping of saline groundwater commenced in 1990 to lower the groundwater gradient to the river to zero thus preventing saline water discharging into the river. Telfer and Way estimated that pumping from the aquifer lowered salinity in the river stream by 46.3 muS/cm. Regression analysis of data that restricted it to three years prior to full pumping commenced and to 3 years after zero gradient was achieved, with sites as categorical variables, estimated a reduction of 58.4+/-9.4 muS/ cm for flows <= 10,000 ML/d resulting in a reduction in salt load of 277 t/d. Regression modelling methodology can be extended to assessments of similar saline groundwater interception schemes.