Inland Waters Theme Report
Australia State of the Environment Report 2001 (Theme Report)
Prepared by: Jonas Ball, Sinclair Knight Merz Pty Limited, Authors
Published by CSIRO on behalf of the Department of the Environment and Heritage, 2001
ISBN 0 643 06750 7
Water quality and sources of pollution (continued)
Salinity of surface waters (continued)
The salinity of water is commonly measured by its electrical conductivity (EC), which is proportional to the concentration of total dissolved salts (on average 1 EC unit equals 0.7 mg/L of total dissolved salts). All states and territories except Western Australia regularly monitor EC as an indicator of salinity.
As part of a joint project between the State of the Environment (SoE) Reporting Unit and the National Land and Water Resources Audit (NLWRA), EC data collected between 1995 and 1999 from monitoring sites across Australia were assessed for exceedance of state and territory water quality management objectives and for trends in EC units. For the exceedance assessment, a three-tiered categorisation system was used to rate the sites and these results were then aggregated to a catchment level. This information was then used to determine whether water salinity was a major, significant or not significant issue in catchments with sufficient information (see Figure 11). Flow-weighted trend analyses were undertaken where there were at least 7-10 years of water quality data. Detailed information on catchment and individual site exceedances and trends in salinity can found on the NLWRA website (http://www.nlwra.gov.au ).
Figure 11: Catchments where instream salinity is currently an issue
Source: National Land and Water Resources Audit 2001a.
As part of an overall strategy to manage increasing instream and land salinity in the Murray-Darling Basin, estimates of the future instream salinity of most rivers in the Basin have been made and are discussed in the following section.
Critical salinities where impacts have been recorded are:
- 800 EC units - World Health Organization upper limit for desirable drinking water; reduced yields for irrigated salt-sensitive crops (e.g. most horticultural crops)
- 1500 EC units - Most horticultural crops, rice, maize and grain sorghum unable to be irrigated; reduced yields for pasture and forage crops; direct impacts on wetlands and aquatic ecosystems
- 5000 EC units - Significant impacts on aquatic ecosystems; cotton, barley, wheat, canola and sunflower only able to be irrigated on well-drained soils using best practice technology.
In most catchments and at most sites in New South Wales, instream salinity was less than 500 EC units. The exceptions were the Namoi, Gywdir, Maquarie, Hunter and Lachlan rivers and rivers in the Coffs Harbour catchment, where between 20% and 35% of sites had salinities ranging between 500 and 1500 EC units. In most catchments there were only sufficient data to assess salinity trends at 25% of sites. At these sites there was no evidence of increasing EC units over the past 7 to 10 years, with the exception of the Macquarie River.
Instream salinity at most sites in the western river systems of Hamilton, Otway and Wimmera-Mallee exceeded 1500 EC units indicating that aquatic ecosystems in this area were under significant stress. At least 50% of sites in the Melbourne and Goulburn-Lodden catchments salinity exceeded 500 EC units. In the Otway, Goulburn-Lodden and Hamilton river systems approximately 10% of the sites showed increasing trends in instream salinity over the last 10 years, although at some sites decreasing trends in instream salinity were found.
Apart from the Murray River and a number of water storages there was little information on the instream salinity of South Australian inland waters. Currently the instream salinity in the Murray River at Morgan is less than 600 EC units with a decreasing trend measured over the past 7 to 10 years due to salt inception schemes and other salinity mitigation measures implemented as part of the 1989 Salinity and Drainage Strategy (MDBC 1989). The instream salinity of the Murray River at Morgan is used as a benchmark for the whole Basin as it is downstream of most of the major inflows and near the major offtakes for South Australia's water supply. Instream salinity is predicted to increase significantly over the next 50 years in the Murray River as the upstream area affected by dryland salinity increases. This is discussed in greater detail in the following section.
In most river systems in Queensland, instream salinity was below 500 EC units. The exceptions were river systems in the Gold Coast and Curtis catchments, where salinity is considered to be a major issue. There were insufficient data to assess many coastal river systems and river systems in the Cape York Peninsula and the Condamine catchment. Apart from 15% of sites in the Gold Coast and Burdekin catchments (that showed increasing trends in instream salinity), there was no evidence of increasing trends elsewhere in Queensland.
Generally Tasmania's inland waters have a low 'natural' salinity compared with mainland inland waters. Based on the available water quality information, none of Tasmania's inland waters has a significant salinity problem. Slightly elevated salinity in some Tasmanian waters can be attributed to effluent from industry, or to mines or sewage treatment plants. There is visual evidence of salinity problems in some small drainage lines and unmonitored waterways (D. Fuller, pers. com.). No data are available to verify the scale of the problem.
There is very little water quality information for the Northern Territory river systems (except for downstream of the Ranger Uranium Mine). Due to the Northern Territory's relatively undeveloped catchments in comparison with other areas in Australia and its higher rainfall, it is unlikely that inland waters would currently have significant salinity problems.
The high salinity of many Western Australian inland waters is considered to be a major environmental and socioeconomic issue and is due to a combination of natural characteristics and human activities in the catchments. Three different drainage types can be defined in Western Australia to explain the salinity of inland waters (WRC 2000c):
- The ancient or old drainage - the arid inland : Rivers, such as the Avon, Pallinup and the Moore, which drain the Yilgarn Plateau in the centre of the state's south-west, are brackish to saline. Most waterways in this region exist as salt lakes or pools and only join the major drainage channels following intense and widespread rainfall. It is during the rare high rainfall events that substantial quantities of nutrients, salt and sediments are flushed from the catchments' soils and transported to coastal waterways. Although many of the inland rivers are naturally saline at times, extensive land clearing in the 1930s, 1940s and 1950s has increased the salinity of the soils, rivers and lake systems. To date, water quality monitoring in the inland regions has been extremely limited due to the highly ephemeral nature of most waterways and their remoteness from populated centres.
- Mature drainage - the semi-arid inland: Rivers draining the wheatbelt, a major agricultural district of the south-west, are predominantly brackish. Much of the land in this low to moderate rainfall area has been cleared for agriculture or mining activities. The lower reaches of the larger river systems that extend into the wheatbelt, such as the Avon, Murray, Blackwood, Warren and Frankland rivers, are dominated by brackish to saline inflows. This is despite freshwater contributions from rivers in high rainfall areas near the coast. Salinity is the most pressing environmental problem in the south-west of Western Australia. The increasing trend in instream salinity in at least some of these systems suggests that the salinity problem is not improving, and in many areas the problem is getting worse.
- Rejuvenated or young drainage: River systems in the high rainfall, coastal areas contain predominantly fresh to brackish water. This zone has been extensively cleared for agriculture or residential land use and, combined with water imported for irrigation, has increased water table levels. Many intensely farmed or populated regions, such as the Swan Coastal Plain and to some extent the area between Denmark and Albany, have elaborate drainage systems and the natural streams have been modified to prevent waterlogging or flooding. This has aided in the rapid transport of nutrients and salt from the catchments' soils to coastal lagoons, inlets and estuaries. Many river systems of the Swan Coastal Plain and of the high rainfall, south-coast region show evidence of increasing salinisation. In contrast, the instream salinity of some rivers in the Preston Basin decreased marginally in the 1990s.
Case study 3: Long-term predictions for the increase in instream salinity of the Murray-Darling Basin river systems
The increasing instream salinity of the Murray-Darling Basin river systems has been recognised as a problem for over 40 years (MDBMC 1989), but until recently there has been insufficient information to accurately predict future basin-wide trends in salinity, the sources of salt in the catchment and the potential economic and environmental impacts of higher salinity. In 1999, a salinity audit of the Murray-Darling Basin addressed these issues (MDBMC 1999). Future predictions of the average instream salinity are presented in Table 14.
|River||1998 (EC units)||2020 (EC units)||2050 (EC units)||2100 (EC units)|
Data refer to the end of the system except the names in italics which indicate river reaches.
Lightly shaded figures indicate that EC exceeds the 800 EC threshold for desirable drinking water.
Dark shaded figures indicate that EC exceeds the 1500 EC threshold for ecosystem and irrigation impacts.
Source: MDBMC 1999.
It should be noted that because of the high variability of saline inflows into rivers and streams, there will be periods of extremely high instream salinity. For example, in the Castlereagh River in New South Wales, over 20% of the EC measurements are up to five times the average. The estimated increases in EC units are not necessary indicative of the load of salts originating from a catchment. For example the Murrumbidgee River will experience only a small increase in instream salinity, but is the second largest source of salt to the Murray-Darling Basin and will double its load of salt delivered to the river system over the next 100 years.
It is predicted that instream salinity of the Murray River at Morgan will rise to 900 EC units on average by 2100 (MDBMC 1999). Rising instream salinity in the main channel of the Murray River from the border to Wellington is of major concern because water extraction for drinking water supply, and to a lesser extent for irrigation, is high in this section of the river. Increased instream salinity will also affect the Albert and Alexandrina lakes and the many associated anabranches and billabongs. Evidence of salinisation is already apparent in off-river water bodies (e.g. floodplain wetlands).
New South Wales
The Bogan, Macquarie, Castlereagh and Namoi river systems will experience large increases in salt loads and instream salinity. The average instream salinity in the Macquarie, Namoi and Bogan rivers will exceed 800 EC units (i.e. drinking water guideline) within 20 years and 1500 EC units within 100 years. Instream salinity in the Lachlan and Castlereagh rivers will exceed 800 EC units within 50 years. These rises have serious implications for future irrigation use and for maintaining environmental values.
A large increase in instream salinity is predicted for the Condamine-Balonne, Border and Warrego river systems, with significant impacts by the year 2020. Once the rising groundwater tables have intercepted the land surface, instream salinity will stabilise and, on average, exceed 800 EC units by the year 2020. Instream salinity will exceed 1500 EC units 14% to 60% of the time.
The western catchments of Avoca, Loddon and Campaspe are already salinised and instream salinity levels reflect this. It is estimated that the Avoca River will experience a significant increase in salinity over the next 50 years whereas the other two catchments will only experience relatively small increases.
The economic impact of current salinity levels in the Murray-Darling River system is $46.2 million per year (MDBMC 1999). This does not include any economic impacts associated with the loss of productive land or reduced crop yield due to dryland salinity.
A study of the economic impact of rising groundwater levels and river salinity on communities in the Upper Macquarie River catchment in New South Wales found that measures to reduce salinity, the maintenance of salt-affected infrastructure and losses in agricultural production cost the community $3.3 million a year (MDBMC 1999). This area has approximately 16 000 hectares of land visibly affected by salinity together with high river and stream salinities. A breakdown of the economic impact on each area of the community is presented in Table 15.
|Area affected||Costs per year ($)|
|Farmers||1 689 396|
|Local Government||154 578|
|Other Government Agencies||632 307|
|Reduced Property values||238 729|
|TOTAL||3 216 958|
Source: MDBMC 1999.
Roughly for every 5000 hectares of land visibly affect by dryland salinity, the economic impact will be $1 million annually. Given that up to 5 million hectares of the Murray-Darling Basin will be affected by dryland salinity in 2100, a rough estimate of the economic impact is $1 billion a year (MDBMC 1999).
The loss of productive agricultural land due to salinisation is only one of the impacts of dryland salinity. Increases in the salinity of irrigation water can also reduce the yield and type of irrigated crops (MDBMC 1999). For every 1 EC unit increase at Murray Bridge in South Australia, costs for agricultural water users in the Murray River catchment will increase by $91 000 a year (MDBMC 1999). The current annual costs of salinity to agriculture is $130 million a year; however, this estimate in considered indicative (Hayes 1997).
South Australian drinking water resources are at greatest risk from the increasing salinity of inland waters. On average, the Murray River supplies 40% of metropolitan Adelaide's potable water and up to 70% in dry years (Jolly et al. 2000). The Murray River also supplies the Upper Eyre peninsula (Whyalla and Port Augusta), the Mid-North and Yorke Peninsula, the Riverland and the Upper South East areas. The remaining areas use groundwater and/or small surface water storages for water supply.
If no measures are undertaken to manage and reduce land and water salinity, the average salinity of the Murray River at Morgan will increase to 900 EC units by 2100. This level exceeds the Australian Drinking Water Guideline of 833 EC units (NHMRC/ARMCANZ 1996) and will decrease the palatability of the water and increase scaling and corrosion of water supply infrastructure (e.g. pipes and pumps). Already the effects of dryland salinity and irrigation induced salinity have caused salinity levels in the Murray River at Morgan to exceed the drinking water guideline 23% of the time (between 1968 and 1994) (Jolly et al. 2000). (See Figure 12.)
Figure 12: Salinity in the Murray River at Morgan (1968-94)
Source: Jolly et al. 2000, reproduced with the permission of CSIRO Australia.
There are two small reservoirs in South Australia currently affected by high and variable salinity. The Todd River reservoir, providing 25% of the water requirements of the Eyre Peninsula, has 3% of its catchment salinised and 79% of it cleared. Middle Dam on Kangaroo Island experiences the inflow of saline water in the summer months (Jolly et al. 2000).
The drinking water resources of 145 000 people in inland New South Wales will be affected by predicted increases in instream salinity (Table 16). This does not include farmers and remote communities that may extract water for domestic uses.
|River basin||Number of people affected by increased salinity of drinking water||Large towns affected by increasing salinity|
|Namoi River||49 000||Tamworth|
|Lachlan River||23 300||Forbes|
|Macquarie River||65 000||Dubbo|
|Castlereagh River||7 900|
Source: MDBMC 1999.
There is no information on the number of people in Queensland and Victoria who will be potentially affected by increasing salinity of their drinking water supplies. Based on the future predictions of instream salinity in Table 14, drinking water supplies of communities in the Warrego, Condamine-Balonne and Border Rivers catchments in Queensland, and the Avoca and Lodden catchments in Victoria are potentially under threat. Increasing trends in the salinity of some of the Gold Coast waterways may also affect drinking water resources in this area.
- Most river systems in south-west Western Australia and some river systems in western Victoria and in South Australia have instream salinities above levels at which impacts to aquatic ecosystems occur.
- Instream salinities of many inland waters are predicted to increase over the next 100 years to levels that are likely to affect aquatic ecosystems and reduce the quality of water for drinking and irrigation. River systems under the greatest threat from increasing instream salinity include the Warrego, Condamine-Balonne, Border, Lachlan, Bogan, Macquarie, Castlereagh, Namoi, Murray, Avoca and Lodden rivers in the Murray-Darling Basin and most rivers in south-west Western Australia.
- The drinking water resources of most of South Australia's population (including Adelaide) and some inland towns in New South Wales, Queensland, Western Australia and Victoria are under threat from increased instream salinity.