Western Australia
Western Australia has the largest area of dryland salinity in Australia and the highest risk of increased salinity in the next 50 years. An estimated 4.3 million hectares (16%) of the south-west region have a high potential of developing salinity from shallow watertables. This is predicted to rise to 8.8 million hectares (33%) by 2050.
In 2000, the risk is predominantly in the eastern wheat belt in valley floors and adjacent areas. Eastern sections of the northern wheat belt also exhibit high risk. There are some coastal areas at high risk around Bunbury and Donnybrook Sunkland. Salinity expansion by 2050 is mainly in the Great Southern and south coast regions.
Figure 10.
The assessment was restricted to the south-west of Western Australia where dryland salinity is widespread. All analysis was based on groundwater depth and trend and the risk of shallow watertables was derived from these two attributes. As dryland salinity is caused by shallow watertables, the risk of salinity is inferred from the risk of shallow watertables. Not all shallow watertables will be saline. Estimates and projected risk areas are based on analysis of existing groundwater levels and trends at a scale of 1:250 000 based on soil systems mapping. There are limitations in the resulting assessment due to gaps in data.
Findings
Table 17.Key assets in areas at risk from dryland salinity in Western Australia.
|
Assets |
2000 |
2020* |
2050* |
|
Agricultural land (ha) |
3 552 700 |
4 181 700 |
6 490 100 |
|
Perennial vegetation (ha) |
600 000 |
710 000 |
1 800 000 |
|
Important wetlands (ha) |
72 500 |
72 500 |
80 000 |
|
Highways (km) |
720 |
840 |
1 500 |
|
Primary roads (km) |
680 |
745 |
1 165 |
|
Secondary roads (km) |
1 200 |
1 425 |
2 325 |
|
Minor roads (km) |
11 550 |
13 650 |
22 930 |
|
Rail (km) |
1 350 |
1 490 |
2 180 |
|
Stream length (km) |
1 520 |
1 700 |
2 850 |
|
Towns (number) |
20 |
22 |
29 |
|
Important wetlands (number) |
21 |
21 |
21 |
* Predictions based on groundwater trends, and `best guess' future land use.
Figure 11.
In south-west Western Australia:
- Groundwater level patterns are dominated by rising or stable trends. No land systems have significant falling trends.
- Of the 4.3 million hectares (16%) of the south-west region potentially at risk from shallow groundwater, 81% is agricultural land.
- Predictions based on current and perceived land uses indicate that approximately one-third of the agricultural areas may be affected by shallow watertables and salinity by 2050.
- Surface water resources in the south-west part of the State are likely to become more saline.
- Approximately 30 000 km of road and rail networks and up 30 major rural towns may potentially be affected.
- Twenty-one of the 54 wetlands located within the agricultural region are potentially at risk of shallow watertables, which may affect wetland health.
- An estimated 1500 plant species will be affected, with 450 possibly subject to extinction.
- Salinisation is likely to reduce fauna species by 30% in affected areas.
- Terrestrial animals will decline significantly (eg. a 50% reduction in the number of water birds using wheat belt wetlands is anticipated due to the salinity-induced death of shrubs and trees).
- Species richness has already declined with the onset of salinity.
An interim assessment of the annual costs of the consequences of dryland salinity is $664 m (Table 18). This is based on `best guess' estimates and does not include any assessment of the costs and benefits of strategies designed to combat salinity impacts on biodiversity.
Key issues
- The most important aspects of salinity investigations in Western Australia will be to determine the impact of different management strategies on groundwater trends at a catchment scale (1:10 000 to 1:25 000) as a basis for improving salinity management.
- Managing groundwater to protect rural towns and associated assets is a major challenge.
Table 18.Annual costs due to watertables/salinity ($m) in Western Australia.
|
|
Best guess |
Possible range |
|
Agricultural land: opportunity cost of lost operating profit |
80 |
80-261 |
|
Rural towns: annuity of a 50 year discounted present value |
5 |
2-16 |
|
Roads: additional repair and maintenance costs |
505 |
Not tested |
|
Railways: additional repair and maintenance costs |
11 |
Not tested |
|
Vegetation: imputed cost of protection of 10% of affected areas |
63 |
63-626 |
|
Total |
664 |
Government responses
In recognition of the magnitude of the salinity threat to agriculture, rural towns and the environment, the Western Australian Government released its first Salinity Action Plan in 1996 (Government of Western Australia 1996). Recently, the State Salinity Council reviewed the plan and developed a strategy that places greater emphasis on community-based programs. Goals of the strategy are:
- To reduce the rate of degradation of agricultural and public land, and where practical, recover, rehabilitate or manage salt-affected land.
- To protect and restore key water resources to ensure salinity levels are kept to a level that permits safe potable water supplies in perpetuity.
- To protect and restore high value wetlands and natural vegetation, and maintain natural (biological and physical) diversity within the region.
- To provide communities with the capacity to address salinity issues and to manage the changes brought about by salinity.
- To protect infrastructure affected by salinity.
The strategy gives priority to managing recharge and discharge, and ensuring a partnership approach between government, science and the community.
One of the major investments in salinity management in Western Australia is the Land Monitor Project. This project is a Natural Heritage Trust and Western Australian State Government initiative to map and monitor the extent of salinity through satellite imagery at the farm and catchment scale. The project aims to provide information about land condition - specifically salinity and the status of remnant vegetation - for the whole of the south-western agricultural region of Western Australia. It is a collaborative project involving Agriculture WA, CSIRO, Conservation and Land Management, Department of Land Administration, Waters and Rivers Commission, and the Department of Environmental Protection and Main Roads Western Australia.
Table of Contents for the Australian Dryland Salinity Assessment 2000
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