Water

3 What are the pressures?

Since the 2008 state of the environment report (EPA 2008), the risks facing our water resources have become more acute as severe and widespread drought has had significant impacts. The ‘millennium drought’—southern Australia’s extended drought that occurred from 2000 to 2010, in some areas beginning as early as 1997—brought a greater appreciation that complex interrelationships exist between the quantity and quality of the state’s water resources and the health of water-dependent ecosystems.

Although the drought has ended, ongoing impacts continue to present significant management challenges. Water overallocation and unsustainable use in some areas, together with land-use change, are major concerns facing the state’s water resources and water-dependent ecosystems. The integrity of river and wetland ecosystems is threatened by human-related activities. Many of South Australia’s rivers and wetlands are affected by flow regulation, catchment disturbance and pest species. In addition, climate change projections suggest that much of South Australia could experience lower annual rainfall and increased temperatures in coming decades.

We need to sustainably manage the balance between competing uses and the environment in ways that recognise climatic variability and maximise the economic, social and environmental benefits. The following sections look at the main pressures affecting South Australian water resources, and particular pressures on the River Murray and Lower Lakes, surface waters and groundwater.

3.1 Climate change

The recent drought that affected the Murray–Darling Basin and other parts of South Australia has highlighted the need for improved understanding of the state’s water resources, and for ensuring that the state’s water planning and allocation processes are more responsive to climate variability and climate change.

Climate projections from the Commonwealth Scientific and Industrial Research Organisation (CSIRO) for South Australia (Suppiah et al. 2006) suggest a likelihood of increased future pressure on the state’s water resources through:

• decreased rainfall in agricultural regions (especially in winter and spring)
• decline in groundwater levels in unconfined aquifers in the long term
• greater frequency and severity of drought, with decreased flows in water supply catchments
• increased flood risk due to extreme weather events (despite drier average conditions)
• higher temperatures, including more extreme hot days, with warming in spring and summer greater than in winter and autumn
• damage to infrastructure—for example, from coastal erosion and flooding.

3.2 Water availability and use

One of the most significant pressures on water availability is expected to come from climate change. With an expected trend of warmer and drier conditions, the amount of water available for all uses and users will come under increasing pressure.

At the same time, population growth in urban and regional areas is expected to increase the demand on drinking water supplies. Expansion of agricultural activities may lead to an increased demand for irrigation water, although increased efficiency in irrigation techniques may help to reduce this demand. Expansion of mining activities in the state will also increase demand for various forms of fit-for-purpose water supplies. At times, more water is needed by water-dependent ecosystems to sustain environmental values; in a changing climate, these needs may become more pressing.

Many forms of current human water use are climate dependent, including some human consumption, private and public uses such as garden watering and open-space irrigation, agricultural use and some industrial use. Climate change will necessitate changes in water use and allocation.

3.3 Land-use change

Land-use changes to support population and economic growth have major implications for the health of water-dependent ecosystems. Relatively unimpacted streams typically occur across South Australia in areas where large tracts of native vegetation have been retained. Southern parts of the state, in particular, have seen significant changes from naturally vegetated catchments to ones where agricultural and urban land uses dominate. Where this occurs, streams are often nutrient enriched and silted, and have riparian zones that are dominated by introduced grasses and weeds.

Land-use changes also affect the quantity and quality of water resources. An example that has received some attention in recent times is the potential impact of forestry in intercepting rainfall that would otherwise recharge unconfined groundwater systems. The anticipated increase in mining activity also has the potential to increase pressure on both the quality and the quantity of water resources. This is reflected in the high priority that has been given to assessing these impacts.

3.4 River Murray and Lower Lakes

Since the early 20th century, Basin-wide flow regulation and diversions for agriculture have reduced the average total river flow at the River Murray mouth. CSIRO (2008) states ‘integrating the flow impacts down through the connected rivers of the Basin shows that total flow at the Murray mouth has been reduced by 61 per cent’. Projections in the same CSIRO report are that, by 2030, the median surface water availability for the Murray–Darling Basin will have fallen by 11% (9% in the north of the Basin and 13% in the south).

From 2007 to 2009, the Murray–Darling Basin experienced the worst drought in more than 100 years of records (see Box 2). Basin-wide climatic shifts resulted in a severe hydrological drought period of extreme low flows. Subsequently, the water level in pool one (waters below Lock 1 located at Blanchetown) fell below sea level for the first time in modern history, with the barrages preventing seawater ingression. The drought resulted in major water quality, ecological and socio-economic impacts across the Basin. Many parts of the South Australian Murray–Darling Basin environment are still recovering from this severe drought event. Persistent legacies of drought include high salinity in Lake Albert, limited ecological recovery in the Lower Lakes and Coorong, submerged acid sulfate sediments in the Lower Lakes, acid drainage from the Lower Murray Reclaimed Irrigation Area, bank slumping and destabilisation, and infrastructure damage.

Other pressures in the Basin include:

• regulated and reduced flows that disrupt flow patterns and biological cues, and prevent flushing and maintenance of a functioning Murray mouth
• nutrient enrichment and high fine-sediment loads; these are exacerbated by land clearing, agricultural practices, urbanisation and stormwater run-off, which promote nuisance algal growth
• intensification of recreational uses (e.g. holiday homes, houseboats and other vessels)
• degradation and weed infestation in riparian zones, associated with farming and livestock access to riverbanks
• increased salinity during low flows, as a result of groundwater inflows and evaporation
• limited refuge habitats in the Lower Lakes due to widespread drying during drought.

3.5 Other surface waters

Pressures in the southern areas of the state largely relate to the change from naturally vegetated catchments to those where agricultural and urban land use dominate. Nutrient enrichment, siltation, weed invasion in riparian zones and dam development affect the condition of streams in the Adelaide and Mount Lofty Ranges, Eyre Peninsula, Kangaroo Island, Northern and Yorke, and South East NRM regions. In many cases, cattle and sheep are allowed access to the streambed and riverbanks, and cropping often occurs up to streambanks.

High salinity and the episodic nature of many streams affect the condition of waterways in parts of the south-east, the eastern Mount Lofty Ranges, central and eastern Kangaroo Island, Eyre Peninsula, the mid-north, and the Willochra catchment in the Flinders Ranges, and streams on the western side of Lake Eyre. In many cases, their generally poor condition is caused by catchment clearance since European settlement and the ensuing mobilisation of naturally occurring salts in soil and groundwater systems, leading to inflows of saline groundwater. However, low rainfall patterns have exacerbated the problems. Such issues exemplify the complex interface between land use, climate variability and change, and local geologies.

Further north, feral animals and stock damage riparian zones and streambeds. Flow patterns in the streams in the Lake Eyre Basin may be affected by management actions in the upstream states. Water abstraction in support of mining and other developments also requires careful management in the arid regions of the state. Rainfall and run-off are highly variable in these areas, and there are few permanent surface-water resources. Surface-water data are generally sparser than in more intensively settled areas of South Australia. Available surface-water data, including rainfall, stream water level, flow rate and salinity, are publicly accessible from the state’s WaterConnect water information website (see Section 4.5.4).

Modification to the terrestrial environment in South Australia has been profound. Given widespread changes to most streams in the southern part of the state, there is likely to be a significant lag before we start to see significant regional-scale benefits from the range of catchment management activities being carried out by government and nongovernment organisations. It may take years before fencing, stock exclusion, buffer installation, erosion-control works, flow-diversion programs and other interventions occur over a sufficiently wide area to lead to major improvements in the environmental condition of our many streams and rivers.

Meanwhile, however, local initiatives undertaken within the framework of activities needed at a broader scale provide modest improvements to the local environmental over a short timeframe.

3.6 Groundwater

Groundwater aquifers face a variety of risks. Water quantity is affected by climate change, as well as the increased use of groundwater in mining and high abstraction rates by industry. Groundwater quality can be affected by contamination from either point or diffuse pollution sources. A number of industrial and commercial activities have contributed to most of the legacy impacts that affect near-surface aquifers in metropolitan areas and rural aquifers in South Australia. These include the production of coal gas during the late 19th to early 20th centuries, which resulted in contamination of underlying aquifers with waste products such as cyanide, metals, polycyclic aromatic hydrocarbons and other hydrocarbons. Between 1940 and 1980, industrial and commercial activities (such as manufacturing factories and drycleaners) that used chlorinated hydrocarbons as solvents led to trichloroethylene plumes remaining in watertable aquifers in part of the western suburbs of Adelaide. Inappropriate disposal of industrial wastes to ‘pug holes’ during the mid-20th century has affected the watertable aquifers in the western suburbs of Adelaide. Service stations and fuel depots across South Australia from the early 20th century to the present are known to have contributed to many hydrocarbon plumes. Agricultural activities since the early 20th century that used industrial fertilisers have contributed to nutrient plumes in both metropolitan and rural areas.

The interconnection of groundwater and surface waters means that impacts on one of these waters will affect the other. The reporting period saw an increase in groundwater contamination incidents in the Adelaide metropolitan area that were responded to by the EPA. The EPA uses a site conceptual model to assess reported incidents of groundwater contamination (Figure 5).

Aquifers in the South East generally have a high potential contamination risk rating because of their karstic nature (which promotes comparatively rapid subterranean drainage), shallow standing water levels, the range of agricultural and industrial operations, and potable (drinking-water) use. Groundwater in the South East is highly valued for agricultural, industrial and drinking-water purposes. Stormwater in Mount Gambier is discharged via disposal bores into the underlying karstic aquifer. High nutrient (mainly nitrate and nitrite) concentrations have existed in the South East for a number of years, with threats apparent to groundwater-dependent ecosystems.

Groundwater is used in southern and western Eyre Peninsula for drinking water. The shallow karstic aquifer in the peninsula is also at a high risk of impact from nutrients and microbiological parameters. This is especially the case in areas where shallow trenches have been dug to access groundwater for stock use.

Areas of the far north are under increasing pressure from mining, with a number of large-scale operations near important groundwater resources (e.g. the Great Artesian Basin). The far north relies on groundwater for domestic and agricultural uses. Mining operations are increasing abstractions of groundwater, with potential adverse impacts on groundwater levels and quality. Abstractions of groundwater occur for mine dewatering, camp water supply, dust suppression, process water use and testing of technologies (e.g. geothermal), and as part of recovery mining, where acid is injected, circulated and extracted to recover uranium. Appropriate management of water from process and hydrogeological testing is also a concern. The energy sector is also a significant user of groundwater in areas such as Moomba.

The increase in managed aquifer recharge schemes (Box 3) in recent years introduced a risk of contamination of deep tertiary or fractured-rock aquifers. Managed aquifer recharge operations inject water (usually stormwater, but also wastewater or river water) of variable quality in winter and then extract most of it in summer. These schemes must be managed to ensure that quality control of injected water is maintained.

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