Salt Discharge Mechanism in the Murray River
Abstract
Groundwater discharge into the Lindsay River anabranch system contributes, on average 75 T/d to the Murray River. Only 35 T/d are derived from direct groundwater discharge into perennial streams within the anabranch system. The remaining salt load is derived from groundwater discharged into the floodplain surface which is then mobilised when over banking into dry floodplain channels and the general floodplain landscape occur under high Murray River flows. A large proportion of the groundwater discharge (to perennial streams and the floodplain landscape) is derived from local groundwater systems within the floodplain, which expand and contract in response to the magnitude and frequnecy of Murray River flooding. As the size of the local groundwater system declines to a minimum of 17 T/d derived from regional groundwater flow. After this condition has been reached groundwater levels in the floodplain continue to decline due to the ongoing groundwater discharge into the floodplain surface. The declining groundwater levels beneath the floodplain indicate that leakage from steam channels, vertical discharge from the Murray Group Limestone and regional groundwater flow are insufficient to balance the groundwater discharge into the floodplain.