The Menindee Lakes are located in south-west New South Wales on the Darling River, about 200 km upstream of the Darling River's junction with the River Murray. The town of Menindee is close to the lakes and the nearest city is Broken Hill.
There are 4 main lakes in the system:
- Lake Wetherell
- Lake Pamamaroo
- Lake Menindee (the largest lake)
- Lake Cawndilla.
The lakes were originally a series of natural depressions that filled during floods. As the flow receded, the water in the natural depressions drained back into the Darling River. Periods of drought and extended low flow can cause the lakes to run dry. Modifications to make use of the lakes for water conservation and regulation along the lower Darling River were undertaken during the mid-20th century.
The lakes are owned by the New South Wales Government and operated by Water NSW.
History
Following thousands of years of Aboriginal habitation, the Menindee Lakes and Darling River became a lifeline for early European explorers in one of the world's most arid regions. Major Thomas Mitchell, Charles Sturt and Bourke and Wills all used the lakes on expeditions between 1835 and 1860.
Later, it was thought that the Darling River would be navigable and provide a suitable route to develop Australia's interior. The township of Menindee became an important access point to the outback. However, the flows in the Darling River proved unreliable, causing difficulties with navigation and water supply. For example, the paddle steamer Jane Eliza took 3 years (from 1883 to 1886) to complete a voyage between Morgan in South Australia and Bourke in New South Wales.
The idea to use the Menindee Lakes for water conservation was first proposed in 1894. However, it wasn't until 1949 that the Menindee Water Conservation Act was passed in the New South Wales parliament. Work started that year, with major works finished in 1960 and overall completion in 1968.
In 1963, the NSW Government agreed with the Australian, Victorian and South Australian governments that water from the lakes could be shared to meet downstream water needs, when the volume of the lakes rises above 640 GL and until it drops below 480 GL.
Catchment characteristics
The Darling River catchment upstream of Menindee is immense and comprises southern Queensland and most of New South Wales west of the Great Dividing Range — an area of 574,200 km². It is only during significant floods that the greater part of this area contributes to the flow in the Darling River.
Two of the most defining hydrological traits of the Darling River are:
- a highly variable flow
- very long flow travel times.
Flows into the Menindee Lakes often occur in large pulses following flooding rain in the upper catchments. Between floods, the Darling River can dry out with practically no inflow at all. Even though large floods can occur at any time of the year, they most frequently occur in March following late summer rains (wet season) in the northern headwaters in Queensland, and from July to September due to late winter rains in the Border Rivers or NSW tributaries.
When floods do occur, it can take several months before the water makes its way along the system to the Menindee Lakes. In addition, a considerable portion of the water is absorbed by the floodplain or simply evaporates as it flows slowly over very flat terrain.
Operational role
The purpose of the Menindee Lakes storage scheme is to capture water:
- for stock, domestic and irrigation needs along the lower Darling River
- to augment flows in the River Murray and assist in the water supply to New South Wales, Victoria and South Australia
- for urban and mining needs at Broken Hill — the Menindee Lakes supply up to 10,000 ML of water each year to Broken Hill — and for other local communities
- for flood management along the lower Darling River
- to provide recreational amenity.
NSW is responsible for operating the lakes to meet local needs, including those at Broken Hill and downstream along the lower Darling River, and also during flood events.
In concert with the Murray–Darling Basin Agreement, we operate the River Murray system on behalf of the NSW, Victorian, South Australian and Commonwealth governments. Under the Agreement rules, we may direct water to be released from the lakes to meet downstream demand when their volume rises above 640 GL, and until they drop below 480 GL.
Features
The works forming the Menindee Lakes Storage Scheme comprise several weirs, 2 inlet regulators, 4 outlet regulators, levees and channels. The works have increased the capacity of the original natural lakes, and allow the regulation of most flows except for large floods.
The 'Main Weir' on the Darling River raises the water to 12 m above river bed level and forms Lake Wetherell. Even during low flow conditions, water can then flow under gravity from Lake Wetherell, passing downstream to Lakes Pamamaroo, Menindee and Cawndilla.
Upstream river gauging stations are used for predicting flows into the Menindee Lakes. There are 2 key gauging stations located at Bourke — about 15 days flow travel time upstream — and Wilcannia, just upstream of Lake Wetherell. Losses on the floodplain of the Darling River and its tributaries can be highly variable, and predicting inflows is difficult.
Releases into the Darling River are made from Lake Menindee and Lake Wetherell. A gauge downstream of Menindee at 'Weir 32' is used to measure the total release into the lower Darling River. Releases can also be made from Lake Cawndilla for supplying environmental flows along the Great Darling Anabranch.
The lakes have a nominal full supply volume of 1,731 GL but, within certain constraints, they can be filled to a total volume of 2,050 GL. The combined surface area of the 4 lakes is about 457 km² when full.
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