The Yarrawonga Weir is the largest of the sixteen weirs on the Murray River. It is operated by the Rural Water Commission of Victoria, under the direction of its owner, the Murray Darling Basin Commission. The storage created by the weir, Lake Mulwala, allows gravitational diversion of water through two main channels to irrigate large areas of land on the Riverine Plains of Victoria and New South Wales. Flood mitigation is a secondary role of the weir.
During winter and spring, when irrigation diversions are reduced, the storage can be lowered by one metre to accommodate flood releases from the Hume Dam and flushes from the Ovens River. Lake Mulwala has sufficient capacity between maximum and minimum operating levels to assist in the "fine tuning" of river flows between the Hume Dam and South Australia. The lake is also a popular recreation resource and tourist venue.
Yarrawonga Weir is one element in a complex system of four major storages, sixteen weirs, and five barrages involved in the regulation of the Murray River and distribution of its waters. The Rural Water Commission of Victoria, New South Wales Department of Water Resources, and the Engineering and Water Supply Department of South Australia integrate with the Murray Darling Basin Commission to operate the various storages and structures. In doing so, they also confront a variety of other issues - environmental recreational - involved in the management of this mighty multi-use resource.
Attempts to manage the Murray River date back to at least 1863. Interstate rivalry hampered the development of any management scheme for the next forty years.
Water was first diverted from the Murray for irrigation in the 1880's. However, it was the succession of drought years from 1895 - culminating in the record dry year of 1902 - that brought home to the residents of the Murray Valley the need for protection against drought, which was needed if the region was to develop.
The "go ahead" for the construction of the weir was given on July 23rd, 1934, and within a few months the preliminary works were in progress. The weir construction started April 26th, 1935 and was completed on July 17th, 1939 with the filling of the lake starting August 12th, 1939. The official opening of the weir was to take place October 27th, 1939, but because of the outbreak of World War II the weir was never officially opened, until October 29th, 1989.
A privately owned hydroelectric station and a fish lift were added to Yarrawonga Weir in 1994. Earthquake proofing works were undertaken throughout 2002. While the Weir Bridge was closed it was modified to a single lane traffic bridge, although it still remains a stock bridge. The $13 million upgrade to the Yarrawonga Weir was officially opened on October 30th, 2002.
The Purpose of The Weir is to:
Raise water level in the Murray River so that gravity diversion is possible via major channels to irrigate land in both NSW and Victoria;
Regulate flows downstream, including the river reaches through the Barmah forest and Echuca; and
Play a role in flood mitigation.
On the NSW side, the Mulwala Canal can discharge more than 7,340 megalitres per day.
On the Victorian side, the Yarrawonga Canal has a discharge capacity of 3,060 megalitres per day.
These two canals service over 800,000 hectares.
Further information: "Harnessed Waters - A River Damned" ed. Noel Loughnan.
