Mon Nov 13

Murray-Darling water buybacks won't be enough if we can't get water to where it's needed

Written by: Avril Horne, Research fellow, Department of Infrastructure Engineering, The University of Melbourne

When it was clear the Murray-Darling Basin Plan could not be completed on time, Federal Water Minister Tanya Plibersek announced a new agreement ^[1] (without Victoria) to deliver in full the plan’s aim of restoring the health of this vast river system.

The new agreement required changes to the Water Act to allow more water for the environment to be purchased from irrigators (water buybacks ^[2]). Concerns about these changes prompted a Senate inquiry.

The report ^[3] from that inquiry, released on Friday, supports buybacks ^[4] but also makes key recommendations to remove “constraints” to water delivery. These are physical constraints or limits to the movement of water through the river system. Managers can only deliver so much water before it spills out of the river onto private land.

The report goes so far as to ask whether constraints should be removed before more water is recovered. This is a question we have been asking in our research. And our results suggest the answer is yes.

Currently, we cannot physically deliver all of the water recovered from other uses for the environment (known as environmental water ^[5]) to where it’s needed without flooding private property along the way. And the government is not prepared to do that.

Basin health is improving but challenges remain

Under the Basin Plan ^[7], about 20% of water used for irrigation a decade ago is now used for environmental purposes. This has improved river health, encouraging fish to spawn and plants to grow, and reduced salt levels in the Lower Lakes and Coorong.

These benefits rely on the river’s flow regime ^[8], not just the annual volume. Higher flows inundate wetlands, move sediment down the river, and provide natural triggers for various species to breed or migrate.

But raising water levels in the river channel isn’t enough to get environmental water everywhere it’s needed. Sometimes larger flows are required. Unfortunately, sending more water down the river runs the risk of inundating private property or damaging infrastructure such as low-lying pumps on floodplains.

Restoring the river’s health requires not only recovering water but also completing projects that allow more of this water to flow despite physical constraints such as a narrow stretch of river. These projects ^[9] might involve modifying or improving infrastructure such as low-lying roads and bridges, as well as working with communities to limit damage and compensate for flooding of private property.

The Senate inquiry report highlights the challenges for these projects. It also supports improving the approach to delivering these projects across the southern basin.

Challenges, priorities and solutions may differ

Our research ^[10] on the Goulburn River in Victoria’s part of the Murray-Darling Basin shows recovery of additional water for the environment does not guarantee environmental outcomes.

This is because the amount of water that can be sent down the river is constrained. So having more environmental water at your disposal does not help, because it is physically impossible to get all the water to where it is needed, when it is needed, without risking inundation of private property.

Current river system operations, including rules and physical constraints, prevent the full volume of environmental water held in Goulburn River being delivered at the right time and in the right way to achieve the best environmental outcomes.

Narrow sections of the river and adjacent private development limit releases from Lake Eildon. River managers are not allowed to deliberately inundate the floodplain if it risks private property.

So the volume of environmental water available in the Goulburn River is not the issue – delivering this water is the challenge. In this regard, Victoria’s refusal ^[11] to sign up to the new basin deal is understandable, because more water buybacks would potentially cause more pain to the local community than gain to the local environment.

However, neither Victoria nor New South Wales has addressed these capacity constraint issues, significantly limiting the ability to get better environmental outcomes with less water. So the challenge is much more complex than simply redistributing entitlements and buying back environmental water.

The elephant in the room: climate change

Temperature, rainfall and streamflow have already changed in parts of the Murray-Darling Basin. Over the coming decade these changes will become more pronounced, widespread and entrenched ^[13], causing more frequent floods and droughts.

While the precise consequences for water availability remain to be seen, the impact on the basin will be immense.

But climate change simply adds to the need to have difficult conversations around the future of communities along the Murray-Darling. Focusing on whether buyback targets have been achieved does not resolve this. In many regions, there will not be enough water, with or without buybacks, to achieve current management objectives ^[14].

Buybacks should be placed in the context of this imminent threat. In rivers like the Goulburn, addressing capacity constraints provides the single best climate adaptation option ^[15] to improve environmental outcomes in the short and medium term.

Removing these constraints would allow more water onto the lower Goulburn River floodplain, with due care for land and infrastructure that could be affected. For example, projects may offer landholders options to avoid or compensate for any water damage and associated costs ^[16].

This is because removing constraints gives river managers more flexibility, which can increase the resilience of the environment to a wider range of future climates. More water from buybacks provides very limited additional benefit because it doesn’t change how environmental water can be delivered.

The senate report emphasises the need to embed consideration of climate change in the Water Act and Basin Plan. The decisions we are making now on water recovery and constraints relaxation will have big impacts on communities.

Our work shows considering climate change is essential to ensuring lasting benefits and resilient outcomes for the rivers and communities that rely on them.

The first basin plan took a big step towards sustainable management of the vast Murray-Darling river system. But it was always meant to be the first step in an adaptive policy process. Priorities and solutions will look different across the basin. We need a holistic approach where buybacks may very well be part of the solution, but are not the whole solution. We also need to ensure we can deliver this water where and when the environment needs it.