Water in some river systems can be controlled so it can be delivered to farmers, communities and the environment when it's needed. Water delivery happens by releasing water from a dam, trading water from a connecting river upstream and by adjusting infrastructure in the river like weir pools to ensure there is enough water in the system at the time it is required.
River operators are responsible for delivering water, whilst also trying not to spill excess water from a dam or allow for extra water to move through the river before it is needed. This is challenging and requires an understanding of:
- the weather forecast and how this might impact the amount of water available and the amount of water in the river
- demands of many different water users and their locations along the river
- how much water is needed to deliver water downstream (known as conveyance)
- how long it will take water to reach a specific section of the river
- whether there are any constraints that might impact when or how much water reaches a particular location.
When the MDBA or other water managers work to deliver water, they take all these factors into consideration.
On this page
Water travel times
When releasing water, the MDBA or other water managers must consider how long it takes for water to get from storage to the entitlement holder who placed the order.
The time water takes to travel can depend on where it's coming from and going to. The rivers in the Basin system are all different. In some places, the river is wide and water moves slowly, leading to more evaporation. In other places, the river is narrow and water can spill out into floodplains. The travel time can also depend on the depth of the river at any given point.
The effects of natural conditions such as weather and evaporation must also be taken into account, although they can be difficult to predict.
For example, if there aren't any floods, it can take three to four weeks for water released from the Hume Dam to reach the South Australian border. If there are floods, and water spreads out into the large forests on the floodplain, travel times can slow to about six weeks or longer.
Operational decisions are made in real-time, so rivers are operated using the best available information at any point in time. For example, operators use the Bureau of Meteorology flood warnings, which are based on the best available current data and the latest weather forecasts. Operators also consider factors like catchment wetness to determine the rate that water will flow.
Constraints on delivering water
A 'constraint' is anything that reduces the ability to deliver water. A constraint can be:
- physical, such as low-lying bridges or private land
- operational, such as rules about when certain areas can or cannot be flooded.
Constraints can prevent the MDBA from running the river system as efficiently as possible.
When the demand for water can't be met (shortfalls)
Water that has been allocated but can't be delivered to users when and where it is needed is a shortfall. A shortfall affecting irrigation water has not occurred in the River Murray system since 2002, however a shortfall is always possible because of the varying factors that need to be considered when delivering water.
A shortfall impacting the delivery of environmental water occurred in the spring of 2018.
Learn more about how the risk of shortfalls is managed
Water losses
Water losses are usually caused by weather and environmental conditions affecting the river. Water losses can happen when water:
- evaporates
- is used by plants
- seeps into the ground.
The MDBA takes water losses into account when calculating how much water to release to meet system demands, including entitlements.
Learn more about why water losses happen
Return flows
After water is used some of it returns to the river system—this water is known as a 'return flow'. Under the Basin Plan, water managers must account for return flows when calculating water in the system.
Learn more about return flows
