Murray-Darling Basin Authority

A succession of dry years from 1895, culminating in the record drought of 1902, brought general acceptance that some drought protection was required to allow further development of the Murray Valley. Thirteen years of negotiation ensued before agreement was reached between the four Governments on the control of waters. In 1911 the three Premiers met in Melbourne for an Interstate Conference and appointed leading engineers from each State. Their task was to present to the Premiers a report and recommendation which might lead to a settlement concerning the question of utilisation of the River Murray and its tributaries.

There was some difference of opinion among the engineers as to the scope of their enquiry, but when their report was presented on 24 July 1913 there were sufficient points of agreement to enable their recommendations to be finalised. The engineers had concluded that what was most needed to permit further irrigation development was regulation by storage. The flow from year to year was so erratic that no scheme for securing complete control was feasible, and so in order to regulate the water supply it would be best to provide for the building of dams or weirs – firstly, to construct a storage of 1 million acre-feet on the upper Murray, and secondly, to convert Lake Victoria into a storage basin.

The River Murray Waters Agreement (later changed to The Murray-Darling Basin Agreement) was ratified in 1915 by the Commonwealth and State Governments by Acts, and proclaimed on 31 January 1917 by the Commonwealth Government. These Acts specified the works which would be constructed under the provisions of the Agreement (including storages on the upper Murray and at Lake Victoria), and set up the River Murray Commission (later to become the Murray-Darling Basin Commission - MDBC) consisting of a representative nominated by each of the contracting Governments.

Advertisement:

The water-sharing principles adopted then, remain fundamentally unchanged today:

• Flow at Albury is shared equally between New South Wales and Victoria;
• Victoria and New South Wales retain control of their tributaries below Albury;
• Victoria and New South Wales supply South Australia with a guaranteed minimum quantity of water, or “entitlement”.

The agreement also provided for construction of:

• A storage on the upper Murray (the site of the Hume Reservoir was selected from 25 alternatives);
• A storage at Lake Victoria;
• 26 locks and weirs extended up to Echuca;
• 9 locks and weirs on either the Murrumbidgee or Darling River (New South Wales later chose the Murrumbidgee).

The Murray-Darling Basin Agreement provides the basis for managing water under Commission control. The most fundamental requirement has not changed since 1915 – the MDBA must conserve water, as well as share and supply it to the three States with minimum wastage. Water controlled by the Commission is shared between New South Wales and Victoria, with both States contributing half of South Australia’s minimum entitlement flow from their share. The States may use their share of water as they like, which has traditionally been for irrigation and water supply purposes. They may, however, choose to use their water for other purposes.

The Murray-Darling Basin Authority is responsible for regulating flow in the River Murray, its anabranches and the Darling River downstream of Menindee Lakes. Water is shared between New South Wales, Victoria and South Australia, according to the provisions of the Murray-Darling Basin Agreement. The Commission does not own any water; it manages water for the three States. MDBA responsibilities were extended in 1970 to provide dilution flows in the Murray to reduce river salinity. Further amendment of the Agreement in 1982 enabled the Commission to consider other water management objectives in its operations. The Agreement still gives precedence, however, to the efficient allocation and supply of water to the States.

Amendment of the Agreement in 1982 enabled the Commission to consider other water management objectives in its operations, such as recreation and environmental needs. This means that operations aimed at meeting objectives other than conserving water and supplying it to the States, must not significantly reduce the volume of water under Commission control.

The MDBA is required under the Agreement to provide a dilution flow at Torrumbarry and Euston Weirs to reduce downstream river salinity levels. Although this may result in some “loss” of water resources, this is accepted.

Water Allocation

During each irrigation season, the Commission assesses the volume of water expected to be under its control so that it can be allocated to the States. Only one assessment may be necessary if resources are ample and the reserve of water held in storage at the end of the season is forecast to exceed 2,500 GL.

River Operations

The MDBA meets State water requirements along the Murray with minimum wastage by:

• Storing water in the wetter winter/spring months and later releasing it during the drier summer/autumn months to meet supply requirements.
• Making releases from the most downstream storage first to minimise loses due to spill.
• Making timely releases from major storages to accurately match water supply with demand, with close attention paid to the time it takes for flow to travel along the Murray. The upper States assist by estimating and advising the Commission of their future requirements at each water offtake point along the Murray, and also by estimating future tributary inflows.
• Using a network of flow gauging stations along the Murray and its tributaries to continuously monitor river flows.
• Utilising mid-river storages to re-regulate flows if supplies do not exactly match demand.

Other operational objectives defined in the Agreement include:

• Providing dilution flows up to 2,450 ML/day and 3,900 ML/day past Euston and Torrumbarry Weirs respectively to prevent the salinity of river water at Merbein and Swan Hill from exceeding 500 EC units as far as possible. These flows are in addition to downstream water supply requirements.
• Providing a depth of water at locks and weirs sufficient for navigation by vessels drawing 1.4m of water.

There are numerous other, often conflicting requirements that the MDBA attempts to meet in its operations. It does this provided that the water conservation objective is not significantly prejudiced. The MDBA would release stored water to meet such objectives, however, at the request of a State, with the water being taken from that State’s share of MDBA available water. Other requirements include:

• Providing flood protection
• Forest irrigation and flooding
• Improving water quality
• Protecting and enhancing the river environment
• Allowing electricity generation
• Meeting recreational needs.

For more information visit the Murray-Darling Basin Authority website.

Advertisement: