Groundwater the known unknown in floodplain management (#55)
The Lower Murray Floodplain is generally a saline environment, both the groundwater and the unsaturated zone. While native vegetation species are highly salt-tolerant, it is essential that sufficient, appropriate salinity, soil moisture is available to sustain growth and life cycle processes. Low salinity groundwater lenses (LSLs) provide an important source of water and support the ecological function of floodplains in an otherwise dry and saline environment. We advocate that the role of groundwater in sustaining floodplain vegetation needs to be more routinely considered in floodplain management.
In recent years, the behaviour of LSLs has become increasingly important in the management of Salt Interception Schemes (SISs). It is important to understand the relationship between pumping volumes and lens development, as this will determine how quickly salt inflow returns to the River and influence floodplain vegetation condition. In addition, the SARFIIP program is developing floodplain infrastructure that will address the continuing decline in ecosystem health and deliver improved ecological outcomes for floodplains along the Lower River Murray. Active management of groundwater to enhance ecological condition and manage risks associated with surface water inundation is an integral part of the program design.
The close relationship between groundwater and vegetation condition needs to be understood to make best use of environmental water. There has been considerable investment in improving vegetation along the River Murray floodplain, and groundwater management may provide one of the most cost-effective interventions, especially where there is existing infrastructure. The learnings from the River Murray are likely to be applicable to other floodplains.