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Dams greater than 100 gigalitres
Water resource development has been integral to the growth of Australia's economy, towns and cities. It has also affected the health of many river systems.
As human settlements and agriculture increased in the nineteenth century, so did the need for reliable water supplies. Australia's unpredictable climate caused highly variable river flows which could not support intensive settlement.(SEE FOOTNOTE 1) Dams were constructed to regulate rivers and store water, primarily for domestic, industrial and agricultural use.
The number of dams in Australia increased during the first half of the twentieth century, but the increase was particularly rapid after the 1950s. Australia now has around 90 major dams, each with a capacity greater than 100 gigalitres (GL). (One hundred gigalitres is the volume of water contained in 100,000 Olympic-size swimming pools). (SEE FOOTNOTE 2) Dam construction and water diversions have influenced the hydrology and ecology of a number of Australian river systems. The patterns of flow in some rivers, once highly variable, have been stabilised and the flow of water has been reduced. Some of the impacts of these changes are discussed below.
Net water use(a)
NET WATER USE
In 1983-84, Australia used an estimated 14,600 GL of water. By 1996-97 this had risen to 22,200 GL, an increase of over 50% in 14 years. (SEE FOOTNOTE 6)
There was some fluctuation in use through the mid-1990s, perhaps in part because of the influence of our highly variable climate, but overall the trend was one of increasing use. Water use rose by 3,600 GL between 1993-94 and 1996-97; a large proportion of this increase is attributed to agricultural activity, in particular livestock, pasture, grains (excluding rice) and other agriculture. (SEE FOOTNOTE 6) There were also increases in the use of water in the rice and cotton industries, with smaller increases for use among farmers growing grapes, or other fruit and vegetables.
EFFECTS OF DEVELOPMENT - WATER QUALITY
The development of water resources has had many effects on our freshwater ecosystems. In 2002, the NLWRA produced an Environment Index that assesses river condition depending on the nutrient and sediment suspended in the water, the catchment and hydrological disturbance, and the condition of streamside vegetation. (SEE FOOTNOTE 5) The degree of modification depends on the extent of change from these factors. A moderately modified river, for example, has a catchment dominated by land uses that disturb the river, with associated water extraction, habitat changes (such as a reduction in streamside vegetation of 50-75% of original cover) and loads of sediment or nutrients above natural levels. Some 90% of Australian rivers were assessed. Among these rivers, the index found that:
Two-thirds of river length assessed in the Northern Territory is in largely unmodified condition, as is about two-fifths of Tasmanian river length assessed. In the other States and Territories more than 80% of assessed river length was moderately modified or worse. (SEE FOOTNOTE 5)
Irrigation and tree clearing have caused rising water tables and increased the salt in groundwater in many places. This increasing salinity is one of the most significant threats to the health of our aquatic ecosystems and our water supplies.(SEE FOOTNOTE 3)
Drinking water for most of South Australia and many inland towns in New South Wales is at risk from increasing salinity. (SEE FOOTNOTE 3) If salinity is not controlled in the Murray River, Adelaide's drinking water has been predicted to exceed guidelines for salinity on two days in five by the year 2020. (SEE FOOTNOTE 3) Nationwide, 80 important wetlands are affected by salinity, and this is predicted to rise to 130 by the year 2050. Many of these wetlands contain species at risk from salinity. (SEE FOOTNOTE 3) The causes of salinity and its impact are discussed in the commentary Land degradation.
The removal of streamside vegetation allows increased sediment into the river, which can add nutrients and pollution harmful to aquatic species and overall river health. This vegetation is seriously degraded in many catchments from clearing, grazing and salinity: in some areas of Western Australia, for example, 50% of rivers and creeks have lost their streamside vegetation and fewer than 10% of wetlands have healthy fringing vegetation. (SEE FOOTNOTE 3)
There are as yet few nationwide data on the extent and impacts of pollutants entering inland waters. Although Australia uses much lower levels of pesticides than other OECD countries, pesticide use is thought to have increased strongly here since the early 1980s. (SEE FOOTNOTE 3) Cotton, rice, sugar cane and horticultural crops are the highest users of pesticides. (SEE FOOTNOTE 3) Since 1990 at least 20 fish kills in New South Wales rivers have been attributed to pesticides. (SEE FOOTNOTE 3) Other pollutants, such as heavy metals and oil, may have localised effects. But in some States and Territories at least, the management of these sources has improved in the views of the State of the Environment Committee. (SEE FOOTNOTE 3) For example, stormwater management plans have been set up for all urban catchments in New South Wales, while the use of pollution licensing systems has increased throughout Australia. (SEE FOOTNOTE 3)
EFFECTS OF DEVELOPMENT - RIVER FLOW
Water resource development has altered the seasonal characteristics, rate and variability of flows in many river systems. For example the flow of the Murray River at Albury would naturally peak in September and be at a minimum in February. Now, water is stored in spring and summer for irrigation, and peak flows, which are reduced, occur in summer, with minimum flows in July. (SEE FOOTNOTE 7)
Ecological processes have been altered by changes in flow patterns and reductions in the size and variability of flows. Natural wetting and drying processes have changed, and many in-stream habitats, floodplains and wetlands have become permanently flooded. (SEE FOOTNOTE 8) This, in tandem with the overall decrease in flows, has led to a reduction in available habitat and also reduced the reproductive cues of many aquatic species. (SEE FOOTNOTE 8, 9) And so the reproductive patterns of both wetlands water birds and native freshwater fish have been affected, leading to a decline in their abundance.
The release of cold water from storages has also affected the reproductive cycle of many aquatic species, (SEE FOOTNOTE 7) while changes in flow patterns have helped exotic species, such as carp, to spread and out-compete native species. (SEE FOOTNOTE 9) Reduced flows are one factor that can lead to more severe algal bloom outbreaks because of stagnation (see box below).
Natural and actual flows per month, Murray River at Albury - 1998-99
NATIVE FRESHWATER FISH
Of over 200 native species of freshwater fish in Australia, the Commonwealth lists (SEE FOOTNOTE 11) species as endangered and (SEE FOOTNOTE 10) as vulnerable to extinction. (SEE FOOTNOTE 12) There are at least six threats to our fish: degradation of habitat; pollution; reduced environmental flows; barriers to fish migration; introduced species; and fishing pressures. The extent of each threat varies across Australia, reflecting differences in water resources and urban and agricultural development. While fishing has played a role in the decline of fish populations, the modification and degradation of fish habitats have had the most substantial impact. (SEE FOOTNOTE 13)
The construction of dams, for example, has altered fish habitat by creating a barrier to movement, altering flow patterns and reducing water flow. Changes to natural flooding regimes have had different effects, such as allowing exotic fish like the European Carp to dominate or out-compete native species (the latter are less able to adjust to the new regimes). This has led to the decline of native fish in the lowland regions of the Murray and Murrumbidgee rivers. (SEE FOOTNOTE 9)
Some 35 exotic fish species have become established in inland waters, with eight identified as having a significant impact. (SEE FOOTNOTE 3) Many were introduced into Australia for ornamental or fishing purposes (and in 1998-99 around half of the fish stocked in inland waters were exotic species). (SEE FOOTNOTE 14) Some of these species, such as trout and carp, are having detrimental effects on native fish. Carp feed by uprooting and killing aquatic plants which native species feed on. The carp thereby disrupt the river bank and stir up sediments which free nutrients that enhance toxic algae (they also contribute to algal blooms by preying on the species which feed on the algae). (SEE FOOTNOTE 15)
Five species of trout and salmon have been introduced to Australia, and over 5.5 million exotic trout and salmon were stocked into our inland waters in 1998-99 alone, although some of these were into artificial compounds where exotic stock can be monitored to try to prevent risk to native fish. (SEE FOOTNOTE 14) Trout have had an impact on the native galaxid family of fish, nine species of which are considered to be at risk. Adult trout are known to eat galaxids, while juvenile trout compete with galaxids for food. (SEE FOOTNOTE 16)
1 Murray-Darling Basin Commission (MDBC) 1990, The River Murray system, The Regulation and distribution of River Murray Waters, MDBC, Canberra.
2 With an olympic swimming pool being 20m x 50m x 1m.
3 State of the Environment Advisory Council 2001, Australia - State of the Environment Report 2001, CSIRO Publishing, Melbourne.
4 National Land and Water Resources Audit. (NLWRA) 2001, Australian Water Resources Assessment 2000, Surface Water and Groundwater - Availablity and Quality, NLWRA, Canberra.
5 National Land and Water Resources Audit. (NLWRA) 2001, Australian Catchment, River and Estuary Assessment 2001, NLWRA, Canberra.
6 Australian Bureau of Statistics 2000, Water Account for Australia 1993-94 to 1996-97, Cat. no. 4610.0, ABS, Canberra.
7 Murray-Darling Basin Commission (MDBC) 2000, Impacts of Water Regulation and Storage on the Basin's Rivers, MDBC, Canberra.
8 Kingsford, R.T. 2000, "Ecological impacts of dams, water diversions and river management on floodplain wetlands in Australia", Austral Ecology, Vol. 25, pp. 109-127.
9 Gehrke, P.C., Brown, P., Schiller, C.B., Moffatt, D.B. and Bruce, A.M. 1995, "River regulation and fish communities in the Murray-Darling River System, Australia", Regulated Rivers: Research and Management. Vol. 11, pp. 363.375.
10 Flett, D. and Thoms, M.C. 1994, "Blue-green algae and our degraded waterways", in (eds) Hirsh, P. and Thoms, M.C., Australasian Geography for the 1990s, Department of Geography, University of Sydney, Sydney.
11 Land and Water Resources and Development Corporation (LWRDC) 1999, Cost of Algal Blooms. Submitted by the Atech Group to the Land and Water Resources and Development Corporation and The Murray-Darling Basin Commission, LWRDC Occasional Paper 26/99, Canberra.
12 The Environment Protection and Biodiversity Conservation Act 1999, Commonwealth Government of Australia.
13 Davies, K.M., Kearney, R.E. and Beggs, K.E. 2000, "Research priorities for Australia's Freshwater Fisheries", Australian Journal of Environmental Management, pp. 28-37.
14 Australian Bureau of Statistics 2001, Australia's Environment: Issues and Trends, Cat. no. 4613.0, ABS, Canberra.
15 Crabb, P. 1997, Murray-Darling Basin Resources, Murray-Darling Basin Commission, Canberra.
16 Cadwaller, P.L. 1996, Overview of the Impacts of Introduced Salmonids on Australian Native Fauna. Australian Nature Conservation Agency, Canberra.