Impacts of irrigation and dryland development on groundwater discharge to rivers—a unit response approach to cumulative impacts analysis

The influence of irrigation and dryland land-use development has increased groundwater recharge, leading to increased discharge of existing saline groundwater and increased the salt load to adjacent rivers. This paper describes further development of a unit response approach to assess the effect and timing of changes to recharge on groundwater discharge to a river. The unit response approach uses a linearised Boussinesq equation to develop an effectively one-dimensional unit response function for a change in recharge to an aquifer some distance from the river. The Glover and Balmer solution for stream depletion is extended from a point sink to an areal source case, and the effects of both a sloping and a bounded aquifer are considered. This approach can provide approximate lead-in and lag times for the impacts of recharge change on groundwater discharge and salt load to rivers. This approach has been applied to estimate the effects of the development of the Bookpurnong Irrigation Area (Loxton, South Australia), and compared with the existing estimates.