Background
Barmah Lake. © MDBA
Photo by: David Kleinert
The Murray-Darling Basin Authority is conducting the Barmah Choke Study to research options associated with river management and the Barmah Choke. The Barmah Choke is a narrow section of the Murray River within the Barmah-Millewa Forest, one of The Living Murray's icon sites. The Choke is an important consideration in the operation of the river, as it restricts the amount of water that can be transferred downstream.
Approximately 25,000 years ago, an earth movement in the southern Murray-Darling Basin caused a slight uplift of land and created what is now known as the Cadell Tilt Block (sometimes called the Cadell Fault). The edge of the block runs roughly north/south not far from the towns of Deniliquin and Echuca. Although only about 12 metres high it is an important feature in this otherwise flat landscape. It eventually changed the course, pattern and character of the Murray River for some 500 kilometres.
After the uplift occurred, a large shallow lake was created by the naturally dammed Murray and Goulburn rivers. The Murray soon found a new course around the northern side of the Cadell Tilt, creating what is now known as the Edward Wakool River System. For thousands of years the Goulburn River continued to feed the lake but it eventually also broke out to the west. Around 8,000 years ago the Murray turned south, breaking through the section between Picnic Point and Barmah, and took over the Goulburn channel downstream of Echuca. The section where the Murray cut through to the Goulburn channel is today known as the Barmah Choke because of its limited capacity to carry flows.
During major floods, large volumes of water are temporarily banked up behind the Barmah Choke. This reduces the height of flood peaks downstream, and floods the former lake area. The regular flooding has created a wetland system now known as the Barmah-Millewa Forest, the largest area of red gum forest in Australia and one of The Living Murray icon sites. These forests contain flora and fauna that would be typical of a region that receives two or three times more rainfall than this area does.
Study objectives
The objectives of the study are to:
- reduce the incidence and magnitude of undesirable (generally unseasonal) watering of the Barmah-Millewa Forest , thereby improving the health of the forest, and conserving water by reducing losses
- reduce the incidence and magnitude of shortfalls and rationing of diversions arising from insufficient channel capacity for bulk water transfer to Lake Victoria
- reduce the incidence and magnitude of shortfalls and rationing of diversions due to insufficient channel capacity to meet demand during periods of peak irrigation usage and during periods of high losses downstream of the Barmah Choke
- enable flexibility to delay transfer of water from the upper Murray storages to Lake Victoria in order to maximise conservation of water resources
- provide capacity for the delivery of water trade from upstream of the Barmah Choke to downstream of the Barmah Choke
- improve the efficiency of delivering water to the icon sites.
- In working toward the above objectives, future stages of the study will:
- maintain the beneficial influence of the Barmah Choke on the flooding regime of the Barmah-Millewa Forest
- identify any significant impacts on the frequency and magnitude of environmental and unregulated flows in the River Murray system, with the aim to minimise these where possible
- identify any significant impacts to other areas or to third parties, with the aim to minimise these wherever possible.
Study phases and progress to date
The main phases of the Barmah Choke Study (see Figure 1) and links to the outputs available to date are:
- Phase 1 (Discovery) - completed
- Phase 2 (Investigation Phase) - completed
- Phase 3 (Individual Options) - completed
- Phase 4 (Options Integration) - current
Figure 1. Phases of the Barmah Choke Study
Next steps
The Options Integration Phase commenced in June 2011 and will model and assess the performance of more promising individual options in combination. It is anticipated that the outcomes of the current phase will be available by early 2012.
