The River Murray is over 2,500 kilometres long and is the major river in the Murray–Darling Basin. It flows through New South Wales, Victoria and South Australia. The Murray–Darling Basin Authority (MDBA) is responsible for ensuring available water is shared to meet the needs of those who depend on water from the River Murray.
When water cannot be delivered to users when and where it is needed it is called a shortfall. This could happen because demand exceeds the physical capacity of the river to carry the water, or when demands for water unexpectedly spike and there’s not enough time to release additional water from dams to meet the demand.
There are 2 different types of shortfall which may occur:
Delivery shortfalls – these occur when actual water use is higher than it was forecast to be when river water was released from the Hume and Dartmouth storages, weeks earlier, to meet the forecast needs for irrigation and water for the environment.
System shortfalls – in these shortfalls, the combined capacity of the system is unable to supply all downstream requirements over the full season.
Irrigators and communities along the River Murray should be aware that there is an increasing risk that water may not be able be delivered to users when they want it.
These risks are not new and change over time.
Key factors that impact water delivery
Changing patterns of demand for water use for consumption, irrigation and the environment.
Changes in land use, including growth in irrigated agriculture.
A variable climate with severe droughts, summer floods and extreme temperatures.
The amount of water the river can carry, particularly through the Barmah Choke.
Water trade drives water to the highest value and the timing and location of demand is variable.
How much water is available and variation in inflows.
Managing the risks
The Murray–Darling Basin Authority, New South Wales, Victoria and South Australia work together to manage water delivery shortfall risks. Together, we’re maximising our ability to meet demand and minimise risks.
Management strategies include:
- operations planning for a range of scenarios from wet to very dry
- monitoring demand and weather forecasts so operations can be adjusted
- using water from tributaries including arranging delivery of inter-valley water transferred from tributaries downstream of the Barmah Choke
- using the storage availability and water at Lake Victoria
- using water from the Menindee Lakes System (when available)
- manipulating weir levels
- managing and restricting water trade through the Barmah Choke.
To date risks have been managed well with no capacity and shortfall impacts since 2002. However, risks cannot be managed to zero.
The impact of a delivery shortfall
If a shortfall happens and water delivery is affected, temporary water restrictions may be placed on water users. Any restrictions will be directed and managed by state water agencies
Actual restrictions are very rare. However, changes in climate, timing and location of demand and land use, combined with the river system’s capacity to carry volumes of water, mean these events are increasing in probability.
The risk is greatest for River Murray water users downstream of the Barmah Choke as the Choke restricts the maximum regulated flow and for much of summer the flow is at the maximum. Upstream of the Choke the maximum flow rate is well above the normal flow rates, allowing peaks in demand to be met.
Planning ahead
Water users need to recognise that shortfall risks exist and there may be times when water can’t be supplied to water users when, where and at the rate it’s required along the River Murray. Being ware of shortfall risks and understanding what the driving forces are for water demand is important. This knowledge will better prepare water users to understand the risk of water delivery shortfall and to take these risks into account when planning and making investment decisions.
Business decisions should factor in the potential risks of water not being delivered.
Information on the risk of shortfall
During the peak irrigation season, the MDBA reports on the current risk of a delivery shortfall in the River Operations Weekly Report.
The MDBA assesses the risk of shortfall by considering the forecast flows coming into the system and demands by irrigators and environmental water holders for the current week.
There are 4 categories which outline the shortfall risk. These are:
- negligible
- low
- moderate
- high.
The risk will be described as negligible when the forecast flow exceeds the anticipated downstream demands and water needed for delivery by a considerable margin. This will often occur when flows are high due to rainfall, which cannot be captured upstream, or when transfers are being made from Hume Dam to Lake Victoria.
A low risk is reported when forecast flows exceed demands but the amount is less than the volume of water that would be considered negligible. This is likely to be the case for much of the season as operators aim to run the system as efficiently as possible with releases from storages matching the expected demand, plus a small buffer.
Moderate or high risk will be reported when forecasts indicate that flows may not be sufficient to meet all demands in the system and deliver water if there is an unexpected peak in demand. It is important to note that a moderate or high risk does not indicate that a shortfall will occur, it simply indicates that the chance of one occurring has increased.
At this point in time this advice relates only to delivery shortfalls and not system shortfalls.
Roles and responsibilities
The MDBA, Basin state governments and their agencies have different roles and responsibilities in managing delivery shortfalls.
The MDBA operates the River Murray system on behalf of a 'joint venture' made up of the New South Wales, Victorian, South Australian governments and the Australian Government. The MDBA is responsible for ensuring available water is shared between the states, managing the system’s assets and directing operations to meet the state’s needs. The state agencies are responsible for distributing their share of available water to individual water entitlements holders and enforcing any water restrictions.
Read more on delivery shortfall risks for Victorian water licence holders.
What we are doing
The MDBA and Basin states governments in the southern Basin have developed shortfall response plans outlining how they would respond as the risk of a shortfall escalates. These plans have been tested and are designed to work together in a coordinated approach.
A method for assessing the risk of delivery shortfalls has been developed. As the level of risk increases additional actions are triggered in the shortfall response plans to mitigate the risk or prepare for a shortfall. Information on shortfall risks during the peak irrigation season is available in the MDBA’s River Operations Weekly Report.
A paper has been developed outlining the risk of shortfall and what has changed to increase this risk. The MDBA and Basin state governments are undertaking ongoing engagement with Basin communities and industries on the increased risk of shortfall.
Feasibility study of options to manage river capacity and shortfall risk
In response to the growing risk of shortfall in the River Murray system, the Murray Darling Basin Ministerial Council has initiated the Barmah–Millewa Feasibility Study. This project identifies and investigates options to maintain and where possible enhance our capacity to deliver water in a culturally sensitive and ecologically tolerable way.
