Land salinity is monitored in a series of focus areas representative of the major regional and local groundwater flow systems (GFS) in the agricultural regions of South Australia.
The long-term collection of monitoring data for each of the three main nationally agreed indicators of land salinity are required for meaningful assessment of land salinity.
- depth to groundwater
- groundwater salinity
- location, size and intensity of salt-affected areas.
Depth to groundwater is generally identified as the most useful indicator of land salinity, as it signifies the presence or potential threat of shallow water tables. An evaluation of long-term monitoring data on the depth to groundwater in the main GFS in a region provides a useful indication of salinity trends. The risk of salinity spread can be related to the type of GFS operating in the area.
Each focus area contains a network of bores to monitor the depth to groundwater. The size of the land threatened can be measured by the rising or falling trends in saline groundwater levels. Rising trends in the average level of groundwater may provide an early indication of an increased dryland salinity risk. Similarly, falling watertable levels may be an indicator of the effectiveness of management strategies.
To interpret salinity trends in each focus area, groundwater data is combined with useful contextual information, including land use, GFS, rainfall variation over time and clearing history, along with the outcomes of previous salinity assessments. Detailed site measurements including electromagnetic surveys over time and soil salinity sampling, combined with the interpretation of aerial photography also help to quantify any changes.
Evaluation of information, from focus areas across the agricultural regions, on groundwater trends combined with location, size and intensity of salt affected areas, provides useful indication of salinity trends across the state.
The future impact and risk of dryland salinity will depend largely on future rainfall patterns, including climate change, the nature of the groundwater systems and the effectiveness of efforts to slow or halt rising groundwater. On-going monitoring and evaluation in focus catchments will inform adaptive management and provide a basis for future salinity assessment.