The Barmah–Millewa Reach

• The Barmah–Millewa Reach is a narrow section of the Murray River that runs through the Barmah–Millewa Forest.

• The current flow capacity of the Reach is around 9,200 ML/day, as measured downstream of Yarrawonga Weir.

• River managers consider the limitations of using the Reach to deliver water downstream.

About 25,000 years ago, an uplift of land created a north-south geological fault in the earth’s surface near Deniliquin (New South Wales) and Echuca (Victoria). This natural event changed the River Murray forever, creating what is known as the Barmah–Millewa Reach – a narrow section of the River Murray that runs through the Barmah–Millewa Forest.

While it is also referred to as the Barmah Choke, it is actually made up of 3 key flow constriction points: the Tocumwal Choke, the Barmah Choke and the Edward Choke.

The forest formed as a result of regular flooding in this section of the river. Because the river is so narrow, flows would often spill over onto the floodplain.

The height and flow of the river has been measured for decades using stream gauges. These records show the daily capacity of the river has reduced by 20% (2,000 ML/day) over the past 30 years. The Reach restricts the flow of the River Murray to around 9,200 ML/day, as measured downstream of Yarrawonga Weir.

During summer and autumn, river managers aim to keep flows at or below channel capacity to minimise unseasonal flooding of the Barmah–Millewa Forest. This constraint provides challenges in meeting downstream peak water use demands and transferring water to Lake Victoria and South Australia, for storage in use even in relatively dry years.

The Reach has led to a restriction in water trade from areas upstream to downstream of the Barmah–Millewa Reach, which must be considered in business planning.

Key facts

The Barmah–Millewa Reach is a narrow section of the River Murray that runs through the Barmah–Millewa Forest.

The Reach is made up of 3 key flow constriction points: the Tocumwal Choke, the Barmah Choke and the Edward Choke.

Trade is restricted downstream of Cobram, Victoria and upstream of Echuca, Victoria.

It runs through the Barmah–Millewa Forest on the Victorian/NSW border.

The Reach restricts the flow of the River Murray to around 9,200 ML/day as measured downstream of Yarrawonga Weir.

It limits the delivery of irrigation water during periods of peak demand, generally in spring and summer.

Trade from above the Barmah–Millewa Reach to below the Reach is restricted to protect delivery of water downstream.

Environmental challenges

The Barmah–Millewa Reach presents environmental challenges for river managers. Operating the river for long periods at ‘top of bank’ levels leads to notch erosion and bank instability.

Unexpected changes in weather and water demands can lead to events such as rainfall rejections, where unseasonal flooding is unavoidable.

The Barmah–Millewa Reach also limits the ability to target the delivery of water for the environment from upstream storages to downstream sites.

Improving knowledge of the Reach

Understanding the river system and how water moves throughout the river helps river operators better understand how water can be managed.

Research from the MDBA shows capacity through the Barmah–Millewa Reach is decreasing. A massive ‘slug’ of sand has been slowly moving downstream – and is now accumulating in the Reach.

Research shows the amount of water that can flow through this section of the river has decreased over the last 3 decades from 11,300 ML/day to 9,200 ML/day. This means around 20% less water can flow through this reach in summer.

The research shows land-use changes – in particular gold-mining, and land clearing along with desnagging and river regulation in the 19th and early 20th centuries — is responsible for introducing large volumes of sediment to the River Murray over a short period of time.

The MDBA and partner governments will consider a number of factors in addressing this challenge. The ecological, economic and community implications of any course of action would need to be carefully considered, along with input from First Nations peoples.

As directed by Basin Ministers, the MDBA will also be undertaking a feasibility study looking into ways to take pressure off the Barmah–Millewa Reach, to support system capacity and reduce the risk of shortfalls in water delivery.

Find out more about the MDBA’s sediment analysis.

Trade and the Reach

A default trade restriction is in place at the Barmah–Millewa Reach – this is necessary to protect water delivery to existing entitlement holders and for environmental reasons.

The restriction means that trade downstream of the Reach may only occur when there is sufficient matching trade capacity available in the opposite direction, which is called ‘back trade’. This means people upstream of the Reach can sell water to buyers downstream of the Reach, but only if the same or greater volume of water has been transferred from downstream to upstream of the Reach first.

Factors that influence the restriction include water availability and allocations, and high demand due to climatic conditions. More information on these factors is available in the River Murray Annual Operating Plan.

Roles and responsibilities

The Murray–Darling Basin Authority (MDBA) is responsible for keeping track of the balance of trade when the restriction activity is in place.

The MDBA also monitors the situation and will lift or adjust the restriction if conditions permit. For example, through the Millennium drought, the trade restriction was relaxed and trade occurred freely from above to below the Barmah–Millewa Reach.

In October 2014, trade from above the Barmah–Millewa Reach reverted to the default position and the restriction was actively applied.