The Barmah Choke is an unusually narrow stretch of river and sometimes the surrounding area — the Barmah Millewa Forest — is inundated so enough water can be supplied to farmers and communities downstream when they need it. Inundation is not considered flooding and can be beneficial for the natural environment. Environmental water holders also release water for the environment to help improve the health of the Barmah-Millewa Forest. Water also flows naturally into the forest. This happens most years following winter and spring rains, but typically, these flows are higher and spread more widely into the forest than managed releases. During wet years such as 2016, natural flows can cover large areas of the forest and bring significant benefit to the environment over many months.
It can be confusing to understand why water is allowed to flow into the forest in a drought. Some people worry that this is a waste of water, or that the MDBA isn't managing it properly.
This page explains
Stories from River — Millewa Forest. An environmental water manager talks about how inundating the forest improves the environment.
Supplying water quickly to those who need it in dry times
There is a limited amount of water that can move through the Barmah Choke. The Choke is one of the narrowest sections of the River Murray. Only 7,000 megalitres of water can flow through the Choke per day without flowing out of the river channel into the surrounding forest. This limits what water can be delivered downstream. Several small regulators have been built throughout the forest to prevent water flowing from the main river channel into the network of creeks that run through the forest. During high river flows these regulators are opened to let water into the forest as would naturally occur rather than having it spill over the riverbank.
When farmers and communities downstream of the Choke are at risk of not getting the water they need, the MDBA may inundate the surrounding Barmah-Millewa forest to ensure enough water flows downstream to meet everyone's needs. This is more likley to be needed when there's very little water in Menindee Lakes, due to drought in the northern Basin.
Releasing water into the Barmah–Millewa Forest in winter and spring helps to keep it healthy
Because the river is so narrow at the Barmah Choke, water has regularly flowed into the area around it during winter and spring since it formed naturally about 25,000 years ago. The Barmah-Millewa Forest ecosystem developed in response to this natural cycle. However, since the Hume and Dartmouth Dams have been built, considerably less water reaches the forest in winter and spring, because dams now capture and store such a large amount upstream. To help offset this, additional water for the environment is now released into the forest to improve the health of the native plants and animals.
If water needs to be delivered through the Barmah–Millewa Forest, so enough water can be supplied to farmers and communities downstream when they need it, the flow is timed for winter and spring so that it also helps improve the health of the forest.
It's important to keep the Barmah-Millewa Forest healthy. This 66,000 hectare forest is home to the world's largest population of ancient river red gums and 74 protected plants and animals. It is a significant feeding and breeding site for waterbirds, and many native fish, frogs and turtles live in its rivers and wetlands. It is an internationally recognised site of unique beauty and holds cultural significance to the Yorta Yorta Nation and the broader community.
Delivering water through the Barmah-Millewa Forest in summer and autumn is avoided when possible
While water does sometimes flow into the forest naturally in summer and autumn, delivering water at this time of year is avoided whenever possible. This is because:
- naturally, high flows are less likely to happen during these seasons
- water in the forest at this time could increase the chance of fish deaths due to poor water quality
- water losses from evaporation would be higher in summer and autumn.
Most of the water that flows through the area around the Barmah Choke is not lost
When the amount of water passing through the river is more than the Barmah Choke can hold, water is allowed to flow into the forest.
Most of this water is not 'lost', but travels across the floodplain back into the river. Some water makes its way into creeks, drains or other channels that lead back to the river. Water also seeps into the ground, becoming groundwater, which can slowly make its way back into the river. This is known as return flows. More water returns to the river during winter and spring, because evaporation rates are lower than in summer and autumn.
The MDBA balances the demand for water and the need to protect the river system
The MDBA is always looking at ways to improve flows through the Barmah Choke to meet water needs and at the same time look after the river environment. While it would be best to always avoid releasing water through the forest in summer and autumn, sometimes it does occur. This is generally when unexpected rain leads to a reduction in irrigation demands and too much water is left in the river. If the resultant river flow increases above the Barmah Choke capacity, some water can flow unintentionally into the forest. However, in recent years, the frequency of these 'rain-rejection' flows has decreased significantly due to improved forecasting and river management.
To help balance competing needs, the MDBA has a trade restriction for the Barmah Choke in place. The restriction means that water can only be sold to users downstream of the Barmah Choke if the same or greater volume of water has been transferred from downstream to upstream of the Barmah Choke first.
The MDBA is currently looking at other options to manage the Choke, including building new infrastructure.
You should know
- Sometimes water is released through low-lying areas of the Barmah-Millewa Forest to guarantee water supply for communities and farmers downstream.
- Most of the water eventually flows back into the system downstream.
- Flows during winter and spring help improve the health of the Barmah-Millewa Forest.
Questions you may have
"Doesn't the inundation of the Barmah–Millewa Forest show the MDBA is mismanaging the river?"
The Barmah–Millewa Forest receives significant water naturally in winter and spring. This is why the MDBA and environmental water holders try to time releases into the forest to occur in winter and spring and avoid these flows in summer and autumn (unseasonal flows) whenever they can. This is true for both releases for the environment and releases to supply other demands such as irrigation.
A range of stakeholders are consulted when deciding to deliver water through the forest. The MDBA works with environmental water holders, First Nations groups, forest managers, state water authorities, river operators, communities and scientists to make decisions. Weather, irrigation demands, the health of native vegetation, birds and fish, and the amount of water in the system all inform the decision. You can read more about the groups that help manage the river.
"Does the Barmah–Millewa Forest really need to be watered? Isn't it a naturally dry forest?"
The Barmah–Millewa Forest formed as a result of water flowing through it regularly for thousands of years. These flows take place nearly every year—particularly in winter and spring—even during most droughts. Because Hume and Dartmouth Dams have reduced the amount of water the forest receives, providing some regular forest flow is very important to help flush nutrients and organic matter through the river. These flows also encourage plants to grow, increase habitat for fish, frogs and turtles, and give fish and waterbirds the cue to breed.
"Are farmers getting less water because of what is lost when the forest it's inundated?"
Most of the water that flows over the banks of the river and into the forest eventually comes back to the river system as return flows and will make its way to farmers and communities downstream.
The amount of water during inundation is taken into account as part of calculating how much water to release. It doesn't get taken out of farmers' water entitlements, but it does mean there is less water available to allocate to all water holders (including environmental water holders) in the future. However, this loss is relatively small, and without it, some water users may not always be able to receive water when they need it. When environmental water holders choose to inundate the forest then any water 'lost' in the forest is debited from environmental water holders' allocations.
"Does the MDBA prioritise delivering water to corporate irrigators over delivering it to others?"
The MDBA does not deliver water to individual water entitlement holders. It simply releases water from storage based on the water orders that are placed by the states and within the rules and policies of the Murray–Darling Basin Agreement and the Basin Plan.
Read more about how water allocations work.
Learn more about flows at the Barmah Choke
