Great Southern Case Study Region, Western Australia
Salt Scenarios 2020
The Great Southern region is located in south-west Western Australia. Land use in the region is dominated by mixed cropping and grazing. The local and intermediate groundwater flow systems typically have low permeabilities and gradients and therefore a low ability to move groundwater. Similar local and intermediate systems are widespread in the agricultural regions of Western Australia and Eyre Peninsula of South Australia.
Salinity risk assessment
Approximately 30% of the cleared land and associated vegetation and water resources are at risk of becoming affected by salt over the next 30 years.
- Continuing current land use systems will result in larger saline areas developing.
- Most of this landscape requires large-scale intervention to change salinity risk with the exception of the steepest, wettest sites in the western portion of the region.
- Widespread adoption of low recharge farming systems may reduce the rate of groundwater rise, and the severity of the impacts, enabling communities and government to `buy time', but it is unlikely to reduce the eventual extent of salinity.
- Although risk may be modified by engineering options, economic and environmental constraints will limit adoption other than in those areas where they are necessary to protect high value assets.
- Two new methods for analysing trends in bore hydrographs were developed. The first provides different linear trends for different segments of the data, and at the same time estimates the amplitude(s) of the seasonal response(s) in the data. The second allows gaps in the record to be inferred using rainfall data, as well as estimating long-term trends and the effect of management.
- Statistically repeatable methods for developing groundwater level maps for large regions with sparse data failed to produce a robust and reliable result.
- Previous methods for producing groundwater surfaces worked well in a local area, but the relationship could not be fitted in other regions.
- The application of the Land Monitor salinity risk maps based on predictions of shallow watertables for equilibrium conditions was useful for extrapolating expert knowledge on the ultimate extent of salinity risk and for identifying assets at risk at the regional scale.
- For the 2.3 million hectares of area mapped for salinity risk, 1157 buildings, 3333 km of roads, 15 682 farm dams and 101 877 ha of perennial (remnant) vegetation are potentially at risk to salinity over the next 20 years.
- For three case study areas in the region that were examined in detail, the discounted value of production losses under the `business as usual' scenario ranged between $800 and $1090 for every hectare of land that is predicted to become saline. In aggregate terms, losses for each of the two 30 000 ha case studies ranged between $4.5 and $6.1 m. The larger of the three case study areas (comprising 107 250 ha) was estimated to suffer losses of approximately $8 m. In addition to these production losses, a significant amount of new damage is expected on infrastructure and perennial vegetation.
- For all but the steepest landscapes, intervention in the form of land use change would need to be substantial and widespread.
- When alternative enterprises (e.g. trees for pulp and timber production) are limited to only the most appropriate soils, the ultimate extent of salinity does not radically change, although the impact is delayed.
- Since salinity risk abatement associated with low-recharge land use systems largely benefits the land they are planted on, these alternative farming systems must be profitable in their own right.
- The non-farm assets at risk require large-scale, local, mainly non-economically-driven intervention.
- Given the scale of revegetation required to substantially change the ultimate extent of salinity, it does not appear feasible with available low-recharge farming systems and tools to make up the gap in farm profitability associated with alternative, low-recharge farming systems.
- While `low recharge high water use' farming will ultimately leave almost as much land at risk to salinity as current practice, the possibility that decades might elapse before the full impact of salinity is realised has considerable social and economic value. If nothing else, it gives families and government more time to adapt to a salinised landscape and possibly for some innovative solutions to be developed.
- Since bore hydrographic monitoring is essential for evaluating the effectiveness of treatments, monitoring systems must be substantially improved in aspects such as geo-referencing, surveying of elevation and spatial coverage of bores.
- Hydrogeological modelling in selected catchments suggests that most remediation strategies do not offer a great deal of off-site groundwater control. Most of the benefits of remediation strategies are local and prevent land from becoming saline because of a treatment planted on that land. This means that with no external subsidies for on-farm costs, treatments should be commercially profitable in their own right if they are to be attractive to farmers and the wider community. This is a key finding and indicates very clearly that farm-based solutions are an important tool and deliver local salinity mitigation benefits.
the technical reports for Salt Scenarios 2020:
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- SS2020 - Overview Report: Using Natural Resource Inventory Data to Improve the Management of Dryland Salinity in the Great Souther Region, Western Australia in PDF format (543 KB)
- SS2020 - Component Report 1 -Modelling Groundwater Depth from Bore Hole Data in PDF format (1.7 MB)
- SS2020 - Component Report 2 - Spatio-Economic Assessment of Salinity Scenarios and Control Treatments in PDF format (89 KB)
- SS2020 - Component Report 2 - Spatio-Economic Assessment of Salinity Scenarios and Control Treatments - Appendix C (Maps) in PDF format (4.8 MB)
- SS2020 - Component Report 3 - The Effect of Recharge Management on the Extent of Dryland Salinity in the Wheatbelt of Western Australia in PDF format (2.1 MB)
- SS2020 - Component Report 4 - The Effect of Recharge Management on the Extent of Dryland Salinity, Flood Risk and Biodiversity in Western Australia in PDF format (5.6 MB)
- SS2020 - Component Report 5 - Application of HARSD Landscape Classification abd Groundwater Surface Mapping Techniques to Study Catchment at Ucarro in PDF format (459 KB)
- SS2020 - Component Report 6 - Analysing Trends in Groundwater Levels in PDF format (333 KB)
- SS2020 - Component Report 7 - Statistical Modelling for Trends in Groundwater Level in Towerrinning in PDF format (1.5 MB)
- SS2020 - Component Report 8 - Land Monitor Salinity Risk Prediction in the Dumbleyung and Mount Barker Regions in PDF format (75 KB)
Table of Contents for the Australian Dryland Salinity Assessment 2000
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