National Committee on Water EngineeringPlease note that this paper is held here for archival purposes, the most up to date papers are currently held on the Engineers Australia website.
This position paper is designed to outline the key aspects of dryland salinity in Australia, and recommend action to address the problem. It is intended to provide summary rather than detailed information, and the reader is directed to the references for further reading. Information on the global aspects of the problem may be found in the references(13). Salinisation also affects irrigation areas, and detail on this aspect will be given in a separate position paper (in press).
Dryland salinity is fundamentally a groundwater problem, although it produces effects at or above the land surface and in the underlying shallow root zone. Along with erosion (by water and wind) and waterlogging, it is a form of land and water degradation that has serious implications for Australia’s future. Dryland salinity can take decades to emerge as a problem. In many instances, it will not be feasible to control or reverse dryland salinity problems, and options need to be developed for living with salinity and managing saline landscapes productively.
The Australian Dryland Salinity Assessment 2000(4) report, part of the National Land and Water Resources Audit (NLWRA), provides a good summary of the key issues (pp2-3), set out in the context of natural resource management.
Salinisation was recognised as a potential problem as early as 1864 in Western Australia(1). The hydrological factors responsible were identified in 1897, and published in 1924 in the Proceedings of the Royal Society of Western Australia. The author was W.E. Wood, a railway engineer working in south-west W.A. to manage fresh water resources for steam engines. His paper also documents dryland salinity on the Eyre Peninsula (S.A.). Further accounts were published by others in 1909, 1917 (during a Royal Commission), 1920, 1924, 1928, 1929, 1938 and 1947(1). However, in the early development of Australia, warnings by some explorers, farmers and scientists were generally not heeded, as Governments sponsored broad-scale clearing for agriculture(2).
The Australian landscape contains large quantities of salts stored in soils and groundwaters. The salt primarily responsible for dryland salinity is sodium chloride (common salt). The original source is primarily from ocean spray carried into the atmosphere and returned to the ground surface in the form of rain and dust. The saltfall is in proportion to rainfall and distance from the ocean. This saltfall decreases from around 100 to 200 kg/ha/annum near the coast to between 10 and 20 kg/ha/annum inland(8). Over hundreds of thousands of years, large quantities of salt have accumulated from saltfall, concentration through evaporation and transpiration, and through weathering of soil and rock minerals. In some areas, salt stocks result more from previous geological periods of sea cover and/or evapotranspiration, rather than being due solely to saltfall and concentration. Concentrations in groundwater similar to and greater than seawater are not uncommon.
Before the European settlement of Australia, hydrological systems were in natural equilibrium. The annual amounts of rainfall and saltfall were largely balanced by outflow in streams, with a slow rate of leaching down the soil profile to the water table. Most water tables were deep below the surface, and a substantial amount of the salt accumulation was stored in the unsaturated zone above the water table under these conditions. In many areas, however, the groundwater itself would have been highly saline. Over the last 200 years, modifications of the land surface, primarily the clearing of land for agriculture, have disrupted this water and salt balance, resulting in salinity problems.
Vegetation removes water from the soil by evapotranspiration, but leaves the salt in the soil, both within and below the root zone. Removal of deep-rooted native vegetation and replacement with shallow-rooted annual vegetation (crops) has resulted in decreased interception and evapotranspiration of rainfall, increased infiltration to groundwater, and a gradual rise in the water table (Figure 1). This has increased the groundwater salinity by remobilising the large salt store in the unsaturated zone that had accumulated over previous millennia.
Figure 1 The Salinity Regime (after Beal, 1993)
Since European settlement, land use changes resulting in rising water tables with increased salinity have ultimately lead to increased discharge of water and salt to the land surface and streams. Evaporation from shallow water tables and surface seepage further increases salt concentrations.
This process of salinisation will continue for a very long time, at least until the increased recharge beneath agricultural land is balanced by increased discharge (ie. until a new hydrological equilibrium is reached). This could take up to 200 years in low rainfall areas. In many areas, the increases in stream salinity are expected to last for hundreds of years, as a new salt balance is eventually established by the leaching out of salts remobilised by the rising water tables.
Salinisation also occurs in irrigated areas, but at a faster rate than occurs for dryland salinity. Excess irrigation water causes water tables to rise quickly to the major evapotranspiration zone. This zone lies at the land surface, and up to two metres below it. It similarly results in increased flows of saline waters from groundwater to streams and rivers. Salinisation in irrigated areas is a problem in all states, but major effects occur in the Murray-Darling Basin, where irrigation areas are concentrated. More detail will be given in a separate position paper (in press).
Dryland salinity is a significant problem in all areas of low to moderate rainfall. The most seriously affected regions in Australia(4) are in the South-West of Western Australia, the Murray-Darling Basin, and the Upper South-East and the Yorke and Eyre Peninsulas in South Australia. Agricultural practices have been the main cause in the development of dryland salinity, leading to a substantial impact on the viability of agriculture over an increasing area of land.
On an Australia-wide basis in 1993, it was estimated that less than 5,000 square km of agricultural land was affected by dryland salinity. By 1996, this estimate had increased to 25,000 square km(5), and this area was considered to be expanding at a rate of 3% to 5% per year. The estimate increased due to expansion of the problem and improvements in assessment methods (this helps account for the minor inconsistencies in Table 1). The latest estimate, published as part of the National Land and Water Resources Audit(4), estimates that 57,000 square km have a high potential for developing dryland salinity through shallow water tables (Table 1). It is predicted that the area affected may increase three-fold to 170,000 square km within 50 years. It will increase further (to an unknown extent) before a new hydrological equilibrium and salt balance is established some time in the next 100-200 years(6).
State |
Area salt-affected in 1996(5) |
Area salt-affected in 1998/2000(4) |
Potential salt-affected area in 2050(4) |
|||
|---|---|---|---|---|---|---|
|
(hectare) |
(square km) |
(hectare) |
(square km) |
(hectare) |
(square km) |
WA |
1 800 000 |
18 000 |
4 363 000 |
43 630 |
8 800 000 |
88 000 |
SA |
400 000 |
40 00 |
390 000 |
3 900 |
600 000 |
6 000 |
VIC |
120 000 |
1 200 |
670 000 |
6 700 |
3 110 000 |
31 100 |
NSW |
120 000 |
1 200 |
181 000 |
1 810 |
1 300 000 |
13 000 |
TAS |
20 000 |
200 |
54 000 |
540 |
90 000 |
900 |
QLD |
20 000 |
100 |
Not Assessed |
Not Assessed |
3 100 000 |
31 000 |
NT |
minor |
Minor |
Minor |
Minor |
Unknown |
Unknown |
Total |
2 470 000 |
24 700 |
5 658 000 |
56 580 |
17 000 000 |
170 000 |
Over half of this area affected by dryland salinity currently occurs in the south-west of Western Australia, affecting about 10% of the agricultural land in the south-west(8). In contrast, nearly all the salt affected soils in irrigated lands are in the Murray-Darling Basin, which also has substantial areas affected by dryland salinity.
More than 5% of presently cultivated land is affected by dryland salinity. This area is expected to triple by 2050. The costs of dryland salinity are difficult to estimate and separate from other degradation costs, but some current estimates amount to around $250 million annually(4), comprising:
Future cost impact estimates are even more alarming. For example, Western Australia’s south-west region produces agricultural goods worth more than $4 billion per annum. It is estimated that increasing salinisation could cost (in present day terms) $300 to $400 million annually in lost production by 2050(8), reflecting a lost capital value of farmland of $3 to $4 billion. These current and potential costs, as well as the capital and environmental cost of lost productive land, are orders of magnitude higher than the budgets applied by government, industry and the community to deal with the problem. Substantial budget increases are warranted to fund ongoing research and innovation. This is Australia’s most significant and extensive environmental problem.
Higher water tables lead to increased discharge of groundwater, and any associated salinity, to streams and rivers. The general trend of increasing salinity in rivers, particularly throughout the Murray-Darling Basin and in the south-west of Western Australia, is of national concern. The salinisation of previously fresh rivers is the most significant off-site impact of dryland salinity.
Dryland (and irrigation) salinity has a major effect on the utility of the River Murray as a widely used water resource, both for drinking and irrigation. Presently the Murray Drainage Basin exports three times the amount of salt than is input from the atmosphere, whilst the ratio for the Darling Basin is closer to 1:1. The large imbalance between input and output of salt is a direct reflection of the increasing salinity and/or quantity of groundwater discharge to the soil surface and to streams. Individual streams exhibit salinity trends that can vary substantially within reaches of the stream(10). Current estimates indicate an economic impact of around $46 million per annum due to River Murray salinity(15), which is predicted to exceed the 800 EC threshold for desirable drinking water quality at Morgan in 50 to 100 years. Even greater rises are predicted in other river valleys, including the Macquarie, Namoi, Lachlan, Castlereagh and Bogan Rivers in NSW, and the Condamine-Bogan, Border and Warrego Rivers in Queensland(15).
Stream salinisation due to dryland salinity in south-west Western Australia has progressed to the extent that 36% of the divertible surface water is brackish to saline, and a further 16% is of marginal quality, leaving a potable resource of less than 50%(8). Attempts to predict future trends have shown that, without any remedial action, salinities in five major streams may increase 15% to 65% in future years(3). At the current rate of expansion of dryland salinity in W.A., the resulting annual agricultural loss (due to stream salinisation) will be around $70 million each year until a new hydrological equilibrium and subsequent salt balance is reached sometime within 100-200 years(8).
Increased flood risk due to greater runoff from areas with shallow water tables has also been identified as a major issue(8). This will be addressed in a Position Paper on flooding (in press – check the IEAust NCWE web site).
The effects of dryland salinity are felt mostly on agricultural land, but they are not limited to these areas. Impacts are also manifest in damage to roads, bridges, buildings, pipelines, communication systems and other infrastructure, where high water tables bring saline water near the land surface. The term ‘watertable salinity’ has been promoted recently to make the dryland salinity message more tangible to all affected, including local government, water and communication utilities, road and railway engineers, industry, householders and landholders.
Although damage to infrastructure due to dryland salinity is acknowledged as a major concern, Councils and public works departments find it difficult to separate out the proportion of their repair costs due to dryland salinity as compared to ‘normal’ maintenance costs. For example, in the south-western region of NSW alone, road damage due to high water tables is costing about $9 million per year, and it is estimated that 34% of state roads and 21% of national highways may be affected(6). The Western Australian government has also identified this as an increasing problem currently affecting at least 500 km of main roads, and has committed funding of $1 million per year in an initiative to protect rural infrastructure affected by dryland salinity(8). It is predicted that dryland salinity will significantly affect more than 30 rural towns in W.A., and more than 60 towns in Victoria.
The relevant biophysical processes causing dryland salinity are generally well understood, and relate to the induced hydrological imbalance. Successful land management decision making in areas affected by dryland salinity requires careful assessment of the relative importance of a range of these interconnected biophysical contributing factors(7), which vary from region to region, including:
However, our detailed knowledge and understanding of the important social processes, and the impacts of dryland salinity on individuals and communities is still developing. It is generally accepted that most landholders are motivated to do something about the dryland salinity, and the social factors contributing to successful salinity management include:
Great improvements have been made in the last 20 years, and we now have quite a good understanding of the biophysical processes underlying the salinity problem. The extent and nature of the problem is highly variable, however, and there needs to be a variability of response to suit physical and market conditions. Recently, we have also begun to improve our understanding of other factors that will contribute to successful management of watertable salinity, including social, political, economic and land management change issues.
It is, however, generally accepted that we have failed to solve the dryland salinity problem, and that there are only a few cases where we have succeeded in managing the problem. The successes that do exist(7) generally occur within fairly small scale catchments, where the causes and effects are readily visible and all landholders are committed to make appropriate land management changes systematically across the catchment (eg. Burkes Flat, Victoria; Liverpool Plains, NSW).
The old adage that prevention is better than cure certainly holds with regard to dryland salinity. Clearing of land, allowed and even encouraged by governments in recent time, is now controlled in most states, and could be further controlled. For example, agricultural land clearing in W.A. has been reduced from 5,624 ha in 1995-96 to 186 ha in 1997-98(8), and landholders have been compensated accordingly.
It is also widely accepted that the dryland salinity problem will generally not be solved within the short to medium term (if at all). In most cases, the only feasible strategy is to ameliorate an inevitable sequence of processes that may cause salinity problems for hundreds of years. The good news is that this is recognised, and that management strategies are now being developed based on ‘what is appropriate for the future’, rather than trying to ‘improve on the past’. The only feasible strategy is currently regarded as salinity management (“living with salinity”) by reducing the severity and extent of dryland salinity, and by protecting priority resources. Substantial changes to feasible strategies may occur within the next decade if carbon credit trading (see later) can be effectively implemented, and/or if improved land and water management practices can be integrated with cropping and market changes.
The fundamental problem remains, as the following example illustrates (for the purposes of this example, Native Title is assumed not to be a factor, which is not to say that it is not acknowledged). Assume we were given a clean slate in terms of uncleared catchments, and we were given the task of developing a sustainable agricultural system for Australia. The aim is to generate the current levels primary production and associated cash flows, to employ the existing workforce, and support the existing rural and regional communities and supporting goods and services sectors. There are currently no known agricultural production (cropping) systems that could generate the current levels of economic and social benefits in the current market, that would not also cause the same degree and extent of degradation that we now suffer.
Dryland salinity is fundamentally a groundwater problem that produces effects at or above the land surface and in the underlying shallow root zone. To develop management plans to address the problem, we need to fully understand how groundwater systems respond to changing recharge due to changing land use, and how the resulting excess water and salt is distributed(4). Groundwater flow systems are not identical across all Australian landscapes, and their contributions to dryland salinity also differ, although there are some broad similarities.
The distribution of three broad types of local, intermediate and regional flow systems have been mapped across Australia, and then classified into 12 specific types using other attributes such as elevation, landscape form, geology and response time to hydrological change (www.nlwra.gov.au/atlas). This classification system can now be used as a framework to help direct strategic policy development, define appropriate management options, and to target investment where actions are appropriate and outcomes are measurable.
From the above, it is clear that implementing actions that significantly reduce net recharge and control or utilise groundwater are essential to maintain or improve the value of agricultural production, and to protect biodiversity, water resources and rural infrastructure. An integrated whole-of-catchment and community approach is essential to implement viable land management options for living with dryland salinity. Required actions(11) can be grouped into:
Most of these actions are documented in various reports(2, 3, 6, 9, 11) and are too numerous to be documented here, although the following comments provide a summary of selected issues and actions.
Improved land and water management practices are the key to managing salinity(2, 4, 11):
There is considerable potential for developing markets in carbon credits (associated with the international greenhouse gas emission treaty referred to as the Kyoto Protocol) to make revegetation financially viable on a large scale (refer to the IEAust Policy Position on Kyoto elsewhere on the web site). This could fundamentally change the current agricultural market, providing new opportunities to implement productive land and water management practices at the catchment scale. This change could effectively provide a new, profitable crop option (eg. oil mallee or other suitable species), which would also help to reduce dryland salinity and meet environmental objectives. This could also possibly reduce the pressure on old-growth forest logging. However, it is still uncertain whether the Kyoto Protocol will be ratified by all parties (particularly while the USA refuses to ratify it), and it will take some time before international and domestic rules for carbon credit trading are resolved.
This involves treating the land and water affected by salinity not as a problem, but as a resource to be utilised for productive purposes, including:
Research, development and transfer activities are required to upgrade technology to support the implementation of actions required to live with the legacy of dryland salinity. This involves:
Some existing national research and development programmes(12) include:
An over-arching programme was announced by the Prime Minister in October 2000 - the National Action Plan for Salinity and Water Quality in Australia. It will be implemented jointly with the States and Territories through the CoAG process. The government has agreed to spend $1.4 billion on the Plan, which is nowhere near what is required to address the issue. For instance, a recent report by the National Farmers Federation and the Australian Conservation Council, “Repairing the Country” identified that $37 billion is required from Governments over the next ten years to address the problem. $700m will be contributed to the Plan from State funds, but it is uncertain whether this will be from existing programs, or whether it will be new funds. The Federal government has previously spent up to around $400m on salinity issues, but these programs have been wound up, so the actual increase in spending will be around $300m of Federal funds.
Engineers and other professionals working in agriculture and water resources have a duty of care with respect to the provision of advice on processes affecting or affected by dryland salinity. Those most likely to be involved are water engineers and hydrologists working as researchers, consultants and government employees. There is a major need for engineers to work closely with other scientists (hydrogeologists, geologists, soil scientists, plant physiologists, agricultural scientists, etc) to encourage a quantitative multi-disciplinary approach. The results of investigations need to be discussed with landholders, and communicated to the community and politicians. This will encourage implementation of new management techniques by farmers at the farm scale and communities at the catchment and regional scale.
The Institution of Engineers position on dryland salinity is that:
For further information, please contact:
National Committee on Water Engineering
The Institution of Engineers, Australia Telephone: (02) 6270 6555
11 National Circuit Facsimile: (02) 6273 1488
BARTON ACT 26000. WWW: ieaust.org.au
Prepared on behalf of the National Committee on Water Engineering by Hugh Middlemis (hugh.middlemis@aquaterra.com.au).
Last updated August 2001.
Last Modified:
Thursday, October 7, 2010 20:45
Comments to: peter.brady@eng.uts.edu.au