mmg.com.au

A new report on the Barmah choke in Murray River has suggested options to reduce unseasonal flooding of the Barmah-Millewa forest.

The aim of the study, which started in 2007, was to develop an understanding of current and potential future water supply and environmental risks associated with the Barmah choke and other mid-river operational issues.

The study reported that the choke restricted the ability of the Murray River system to meet the demands of irrigators and other water users, and to manage high summer flows through Barmah-Millewa Forest.

The choke is the relatively narrow section of the river through the Barmah-Millewa forest which reduces the maximum flow to about 8000Ml/day.

The options recommended from the final report include:

■Modifications to the rules governing inter-valley trade transfers to modify shortfalls;

■Altering the ‘‘six-inch rule’’, which limits the rate of fall of river level at Doctors Point downstream of Hume Reservoir to a maximum of six inches (or 150mm) per day. This rule was ‘‘adopted to provide adequate warning of river level changes, and to minimise bank slumping’’; and

■Using the Perricoota Escape as a bypass route.

The Deniboota Canal offtakes from Mulwala Canal downstream of Deniliquin and runs south-west, connecting to Murray River just upstream of Torrumbarry Weir via the Perricoota Escape.

The Perricoota Escape originally had a capacity of 50Ml/day which was used to deliver water through the system to Murray River. In 2006 Murray Irrigation Limited upgraded the capacity of the escape to 200Ml/day to provide flexibility in diverting water around the Barmah choke.

A spokesperson for Murray-Darling Basin Authority said the study would feed into the work MDBA was doing to look at constraints in Murray-Darling Basin, as required under the basin plan.

‘‘The final decision on which options, if any, will be adopted will sit with representatives from basin governments.’’

The final report on the Barmah Choke Study was made publicly available mid last year shortly after it was finalised.

The spokesperson said it had long been recognised that the Barmah choke was a natural bottleneck in the system which limited how much water could be delivered to downstream water users in summer and autumn without causing unseasonal flooding of Barmah-Millewa Forest.

The study drew on the local knowledge of irrigation companies, forest managers and river operators on the Murray.

Further discussions with local stakeholders will be held in coming months and will be organised through catchment management authorities.

For further information and a copy of the report, go to the Murray-Darling Basin Authority website: www.mdba.gov.au