The dwindling river: Effects of weirs, locks, barrages and dams

In a bid to control the Murray to assist navigation, and to aid the extraction and harvest of fresh water for domestic and industrial use, a combination of 146 structures including dams, barrages, locks, weirs, bores and channels and have been built over the past 70 years. Collectively these structures accumulate in excess of 15 million megalitres of water annually, which leaves little for river flow.

The Murray-Darling Basin supports and contains a quarter of Australia's cattle and dairy farms, half of the sheep properties and cropland, and three quarters of the national irrigated land as well as the two million people who live in it. The industries reliant on the regulation of the river contribute approximately $10 billion to the Australian economy through annual production.

For South Australia, in an average rainfall season, the River Murray supplies one half of South Australia's stock, domestic, irrigation and industrial water. In a dry year, up to 90 per cent of Adelaide's water supply comes from the Murray. In South Australia nine locks, weirs and five barrages combine with numerous interstate upstream structures to regulate the water flows in the River Murray. This has created a slow flowing river of nearly constant level and supply. However, this is a huge contrast to the natural regime of the river which varied from the extremes of freshwater flood peaks in spring to highly saline waterholes in the summer months.

The regulation of the river's flow and development on the floodplains around the wetlands has greatly reduced the frequency and duration of ecologically beneficial flooding. This impacts on the numbers of waterbirds that rely on frequent flooding to breed and raise their chicks.

Weirs and locks have affected water levels in the river, creating permanently flooded areas just upstream of the structures. This has been responsible for the many dead river red gums seen upstream near the weirs. The still waters held by dams and weirs provide ideal conditions for the breeding and growth of carp, redfin and other introduced pest fish, and noxious waterweeds such as Water Hyacinth and Salvinia. (link to Introduced Species)

River structures pose problems for migratory fish, impeding their migration up and down the river. Free movement within the river system is a fundamental part of the lifecycle of many native fish species.

In the lower reaches of the Murray near the mouth, the barrages have changed the lower lakes (Lakes Alexandrina and Albert) from an estuarine environment to freshwater. This has had drastic consequences for those species that migrate between freshwater and the sea, and has promoted the growth of freshwater plants that encourage the deposition of sediments which extend the land into the lakes. The construction of the barrages across the low reaches of the Murray has led to the growth and stabilisation of a flood tidal delta, a triangular alluvial tract known as Bird Island at the mouth of the river. This may eventually close off the river mouth.

Cold water discharges from irrigation storage dams make conditions unsuitable for native fish and plants for up to 100 kilometres downstream, which allow exotic species to proliferate.

The creation of dams, weirs and reservoirs on the Murray has created a series of stable artificial pools which aggravate salinity in the river.

Some of the effects of these developments and use of the Murray's waters that are now appearing are the result of over a century of use and the solutions are complex. The biggest problems are seen as being water quality, (particularly salinity), water quantity, the control of introduced species and the control of pollutants.

Definitions

What is a weir?

A low dam that is built across a river to raise the water level, divert the water, or control its flow.

What is a lock?

A section of a canal or river that may be closed off by gates to control the water level and the raising and lowering of vessels that pass through it.

What is a barrage?

A barrage is a construction across a watercourse to increase the depth of water to assist navigation or irrigation.

What is a dam?

A barrier of concrete or earth built across a river to create a body of water as for domestic water supply, or a reservoir of water created by such a barrier.

Definitions sourced from: The Australian concise Oxford dictionary of current English / edited by Bruce Moore, Melbourne, Vic.: Oxford University Press, c1997 3rd ed

and Word Reference

Weirs, locks, barrages and dams in South Australia

Barrages

There are five barrages in South Australia: Goolwa Barrage, Mundoo Barrage, Boundary Creek Barrage, Ewe Island and Tauwitchere Barrages, which were built between 1935 and 1940. Before the barrages were built, saltwater could reach as far upstream as 250 kilometres from the Murray Mouth, and river levels could fluctuate considerably.

Locks and weirs

Ten weirs were constructed to allow navigation along the River Murray from Lake Alexandrina (near the river mouth) to Wentworth, New South Wales. South Australia constructed the nine downstream weirs, and New South Wales constructed weir 10. South Australia operates weirs 1 to 9 and New South Wales operates weir 10.

• 1922   Lock & Weir 1 - Blanchetown
• 1928   Lock & Weir 2 - Waikerie
• 1925   Lock & Weir 3 - Overland Corner
• 1929   Lock & Weir 4 - Bookpurnong
• 1927   Lock & Weir 5 - Renmark
• 1930   Lock & Weir 6 - Murtho
• 1934   Lock & Weir 7 - Rufus River
• 1935   Lock & Weir 8 - Wangumma
• 1926   Lock & Weir 9 - Kulnine

Dams

Dartmouth Reservoir, in Victoria is the Murray-Darling Basin Commission's largest storage and when full represents 44 per cent of the system's total storage capacity. Its primary function is to increase security of supply. It also provides increased annual supplies of water to New South Wales and Victoria and has increased the minimum annual entitlement to South Australia from 1,550 to 1,850 gigalitres.

There are no dams of this nature on the River Murray in South Australia.

Further Reading

Jensen, Anne (Ed.) River Murray barrages environmental flows : an evaluation of environmental flow needs in the Lower Lakes and Coorong : a report for the Murray-Darling Basin Commission, Canberra : Murray-Darling Basin Commission, 2000

Linn, Rob. Murray water is thicker than blood : the stories of the families who made the River Murray's locks and barrages, Waikerie, S. Aust. : Historical Consultants for River Murray Locks & Barrages Reunion Committee, 2001

Launer, Doris L. William R. Randell Lock, lock and weir no. 1, Blanchetown : general and historical report, [Blanchetown, S. Aust. : D.L. Launer], 1986

Links

Murray-Darling Basin Authority See: Water in storages and River operations

River Murray Urban Users Committee See: Resources: RMUUC Fact Sheets: River regulation and diversion