Constraints management is about investigating small overbank flows to give key wetland habitats a much needed drink, while avoiding any major impacts on people or property.
Constraints is the term given to features such as crossings, bridges or low lying private land, or river practices and rules, which can restrict when and how much water can be delivered from water storages.
These constraints mean we are not managing the system as efficiently as we could. Basin states asked the MDBA to develop a constraints management strategy so water can get to where it’s needed, when it’s needed most, while preventing or mitigating potential effects on third parties.
Basin states are currently completing the second phase of the strategy and working with communities to investigate changes to flow heights in rivers.
Floodplain health and overbank flows
Floodplains are the kidneys of the Basin, they play an essential role in filtering out our rivers and keeping them healthy. The connection between rivers and floodplains is also vital to help:
- flood dependent vegetation in forests and wetlands, particularly in the mid to lower ends of river systems
- improve the capacity of rivers, floodplains and wetlands to recover after droughts or floods
- recharge soil moisture and improve fertility of the soil
- provide habitat and cues for fish and bird breeding
- support the food chain
- improve water quality by flushing saline pools and by reducing the frequency and severity of blackwater events.
The construction and operation of large dams to support towns, industry and irrigation has allowed communities to prosper through storing more water upstream for productive use and providing additional flood protection. However, this means rivers cannot connect with floodplains as often as they need to for the whole system to stay healthy.
Constraints is not about recreating large damaging floods affecting towns, homes and infrastructure. Constraints work is about looking to increase how often small overbank events happen in key areas of the Basin and investigate what effects these changes could have on riparian landholders and how these effects could be addressed.
McKennas lagoon – the effects of going without water for too long
At the moment, many areas of floodplain go without water for too long. This means plants and animals are struggling or are no longer found in certain areas, and it can take a long time to return or may not be able to return at all. The following photos of McKennnas Lagoon near the Murrumbidgee River show what can happen if wetlands go for too long without a decent drink.
This lagoon would have filled up several times during the Millennium Drought, but because of regulation and consumptive use, it remained dry for ten years. The dry period lasted too long for the seed bank and vegetation rhizomes, which were unable to recover when water finally arrived. For the seedbank that may have survived, the flows also brought with it leaves and sediments which had accumulated on the floodplain during the drought, causing a large blackwater event, and likely killing small plants that may have started to grow. These conditions meant the water plants were not able to re-establish in the lagoon, even after it had been full for six months.
To help prevent what happened at McKenna’s lagoon from happening to more wetlands across the Basin, constraints is investigating ways to water and flush out some areas of the floodplain a little more often and provide more frequent water to the areas that need it most.
Constraints management strategy – because a river is more than just a channel
Basin governments asked the MDBA to develop a constraints management strategy on their behalf to improve the health of the floodplain in key areas of the Basin
The constraints management strategy sets out a process for:
- investigating small overbank flows to connect rivers to floodplains more often for a healthy floodplain environment
- investigating any impacts of these flows on people and property
- ensure any effects of these flows can be addressed before the flows proceed
- making the most efficient use of environmental water .
Basin States are currently completing the second phase of the strategy and working with communities to investigate changes to flow heights in rivers. These changes are not about creating damaging floods affecting towns, they are about investigating small overbank flows. By allowing flows of this size, key wetland habitats get a much needed drink, while preventing or mitigating any major impacts on people or property.
The effects of flows and community thoughts
The effects of addressing constraints will vary across different areas in different river catchments. In the upper river catchments, such as the mid to upper Murray, Murrumbidgee and Goulburn Rivers, landholders are likely to have benefitted from the flood protection provided by dams and generally do not need or want higher flows. However, further downstream where native pasture grasses rely more on overbank flows, landholders generally welcome a return to a more natural regime that will deliver both productivity and wider environmental benefits.
Some of the key benefits for communities by addressing constraints include:
- increased pasture growth for floodplain graziers
- funding for on-farm infrastructure improvements, such as new bridges or crossings
- funding for upgrades to ageing public flood infrastructure, such as levees, roads and crossings
- better water quality as saline pools are flushed out and floodplain litter washed away to reduce the severity of blackwater events
- recreation and tourism associated with the higher flows and healthy wetlands, such as increased fishing, kayaking and camping.
Local communities have also said there will be some temporary third party effects if small overbank flows were to be delivered, such as:
- inundation of private low level crossings
- increased maintenance of private levees
- isolation of crops and stock
- inundation of very low lying paddocks
- increased risk of flooding.
Community feedback in this process is paramount and Basin states are doing more work to make sure any concerns, such as increased flood risk, are fully explored before any flows proceed. If a decision is made by Basin water ministers in 2016 to go ahead with addressing constraints, no flows will be delivered until preventative measures are in place to mitigate any impacts such as those outlined above.
What are people saying about constraints?
Basin communities have been involved with constraints since 2013. State governments have led conversations with the community since 2015, with some support from the MDBA.
There are a range of views about what addressing constraints could mean for different people.Some of the feedback received by the MDBA is listed below:
"As far as I am concerned the more water you use in winter and early spring the better — I’d like to see airspace in those dams. It’s the big floods I’m worried about."
- Farmer west of Wagga Wagga
"The flow rates being investigated are too high, the flood risk as a result of these kinds of flows is unacceptable."
- Landholder, Constraints meeting in Deniliquin, 2015
"There are benefits to a flood, but there are issues as well. We may be able to live with a few inconveniences — shifting a few cattle is not too big an issue if we get enough notice. However, although there is a level of inconvenience that we can all tolerate, there are flow events that are just too big and too damaging that should not be considered."
- Cattle farmer near Molesworth
"In the Edward–Wakool system, combined regulated and unregulated flows are generally looking after the environment here. Our issue is with the ephemeral creeks, that’s the downside of regulation and consumptive use. You need to think about smarter ways to get water to those."
- Community member, Constraints meeting in Barham, 2013
"Grazing occurs on very low country that gets wet even in small flows (<250 ML/day). The higher the flows, the more area to get wet. This means that in dry years the soil moisture in these paddocks is good and generally retains this moisture even in dry years. This helps for cattle production."
- Gwydir landholder, 2015
"40,000 ML a day is still unacceptable to most of us — anything above that is completely unacceptable to all of us."
- Riparian landholder near Howlong, 2014
Changes to running the river – updating river management practices
River management practices have largely evolved to support irrigation and navigation. This means that it can be hard to use environmental water optimally. To remedy this, we have investigated new practices to deliver environmental water more efficiently, without affecting water holders. Some of the key ways to get more out of all the available water in the system is through:
- protecting and using environmental releases throughout the length of the rivers (known as shepherding)
- environmental water from dams when unregulated rivers are already running (known as piggybacking).
The new practices are an important factor in achieving the Basin Plan’s outcomes and Basin governments have all agreed to them as part of the Plan. Any decisions to change Basin river operating rules or procedures can only be made by Basin governments, either collectively for the River Murray, or individually for other rivers in the Basin.
Constraints and supply measures – seeing the benefits with less water
At the moment the Basin Plan says 2,750 GL needs to be recovered for water use in the Basin to remain sustainable, but this volume may change under the Sustainable Diversion Limit (SDL) adjustment mechanism.
Addressing constraints means better environmental outcomes through more efficient use of environmental water, and so constraints proposals will be considered as part of a package of measures under the SDL adjustment mechanism, which include constraint, efficiency and supply measures.
It is the responsibility of Basin states to propose SDL adjustment measures. The latest SDL adjustment proposals (including constraints) can be found here.
If constraints were addressed, and similar environmental outcomes could be achieved without needing as much water, there is a chance that some of the constraints projects may be approved as supply measure projects.
What has been achieved so far
During 2014, we undertook the prefeasibility phase of the constraints management strategy. The findings of this phase were presented in our reach reports for each of the seven identified priority focus areas: Hume to Yarrawonga; Yarrawonga to Wakool Junction; River Murray in South Australia; Gwydir; Murrumbidgee; Goulburn and the Lower Darling.
Our first annual progress report was provided to ministers in December 2014, and included findings and recommendations to Basin governments about which constraints measures should be progressed to the second phase.
The second phase (feasibility) is currently underway. During 2015, we undertook technical work on behalf of Basin governments, and on request, assisted Basin states with stakeholder consultation. This work has provided the basis for further development of constraints proposals and stakeholder consultation by states.
What’s next for constraints
Constraints proposals will result in recommendations to Basin water ministers (due in June 2016), who will decide whether it is practical or not to make the recommended changes.
No decisions have been made about changing the way the rivers are currently managed. If Basin water ministers make a decision to go ahead with constraints, higher flows would not be delivered until the potential impacts on people and property have been fully addressed. It is expected that this could take up until 2024.