The lower River Murray flows through a region where the groundwater is naturally very saline. Salt in groundwater flows from regional aquifers into the floodplain, where it can be stored – in the groundwater, soil and backwaters, or can flow into the river. In the past century, the salt moving into the floodplain has increased due to land clearance and irrigation, while freshwater flows in the river have decreased.
The presence of salt complicates management of floodplain and river health. Efforts to reduce the salt entering the floodplain have included irrigation infrastructure improvements, and wells to intercept groundwater flow (the salt interception schemes). Once the salt is within the floodplain, management options include groundwater pumping, freshwater injection, and environmental watering.
Numerous models have been used to estimate the movement of salt into and out of the River Murray floodplain; they differ in purpose, scale, data requirements, accuracy, and cost. Long-term salt flows into the floodplain can be estimated using flownets, semi-analytic models such as SIMRAT, and numerical groundwater models. Salt accumulation and release within soils has been simulated using unsaturated zone models, but data requirements have limited their use and interpretation. Salt movement within floodplain aquifers is driven by short-term processes which the latest generation of numerical models strive to emulate, but significant limitations remain. The modelling also needs to indicate the groundwater response to management actions to help inform ecological understanding of benefits and trade-offs and adaptive management decisions.