Area of land threatened by shallow or rising watertables: Depth to groundwater
Indicator Status: Agreed
Department of the Environment and Heritage
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Why do we need to measure depth to groundwater
Rising trends in the average level of watertables may provide an early indication of an increased land salinity risk in a catchment. Similarly, falling watertable levels may be an indicator of the effectiveness of mitigation strategies (Coram, Dyson & Evans 2001); it may also be a consequence of reduced recharge due to climatic factors or increased groundwater extraction from bores. Static watertable depths indicate that recharge to the aquifer is equal to discharge.
- By monitoring watertable levels, we can identify whether and when groundwater levels are rising, falling or remaining static; and hence the areas at risk from salinity (DNRE 2001).
Rising watertables may not be of immediate concern in a catchment where the unsaturated zone is tens of metres thick. However, immediate remedial action should be triggered when levels reach the capillary zone (approximately 2 m below ground surface).
How will monitoring depth to groundwater help fight salinity
Basins or catchments with rising groundwater pressures have been identified as having salinity problems. Monitoring the trend in groundwater pressure at local, intermediate and regional scales provides a way to assess salinity risk at any level (from catchment and sub-catchment level through to the national level) to determine and prioritise actions to attain sustainable natural resource management.
- Knowledge of water table levels provides an overview of groundwater trends (DNRE 2001). Although depth to groundwater in confined aquifers is not an indicator of salinity risk, this information may allow assessment of whether inter-aquifer leakage is occurring in a catchment-monitoring of watertable trends provides information about change in groundwater pressures and likely discharge volumes in response to changes in recharge (NLWRA 2002).
- Data can assist in understanding catchment and sub-catchment hydrogeological systems.
State assessments of the NLWRA Water Resources Assessment have identified a number of significant information gaps and method limitations in our ability to evaluate the exact extent of dryland salinity and the likely effectiveness of management responses. Major deficiencies exist in the design and coverage of groundwater monitoring networks-even in Victoria, Western Australia and South Australia, where monitoring sites have been established, significant gaps limit our ability to evaluate effects of land use responses.
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