How water is allocated
Water sharing plans developed by DPI Water in consultation with the community determine how much water can be extracted over the long-term and how much needs to be set aside for the environment.
The volume of water licensed users can have, known as an allocation or Available Water Determination (AWD), varies from year to year based on the licence category and size of their individual entitlement. This allocation is dependent on a range of factors including dam storage levels, river flows and catchment conditions.
The main licence categories below are allocated water in the following approximate order of priority:
- Domestic & Stock
- Town Water Supply
- High Security
- General Security.
Allocations at the start of the water year
At the start of each new water year on 1 July, licensed water users are provided with an opening allocation for each category. This may be anywhere between zero and 100 per cent of their full entitlement.
For most licence categories, if 100 per cent of entitlement is allocated, then there is no more increase in that licence category for the remainder of the water year. However, if a licence holder receives less than 100 per cent of entitlement, then an increase in allocation can occur, if sufficient water becomes available.
Domestic, stock and town water supply
Opening allocations for Domestic, stock and town water supply are generally 100 per cent unless conditions are very dry with low water in storage.
High security, conveyance
Full or near full High Security allocations are made at the start of all but the very dry years and Conveyance allocation is made commensurate with other allocations.
General Security licences are the last to receive allocations and are therefore the least secure licence category. They can start the year with low or zero allocation and typically receive incremental improvement as the year unfolds commensurate with rainfall and runoff. General security licences are the most susceptible to seasonal climatic variations.
Resource Assessment Process
When determining how much water will be allocated to water users, there are number of considerations, including:
- How much water is in storage and how much of that is carried over as unused water from the previous year, including undelivered inter-state trades, where applicable
- How much water is expected to flow into storages from natural inflows over the forecast period
- The volume required to run the river, including end of system flows, transmission losses and evaporation losses
- Other requirements, including storage reserves and credits to environmental water allowances, where applicable.
In making the water resource assessment, the lowest recorded inflow sequence as at the commencement of the first water sharing plan is used so that DPI Water only allocates water that is very likely to flow into the storages. Not all inflows contribute to increasing allocations.
Below is a 'simple' overview of how water is allocated in valleys in NSW. A larger copy is also available (JPG, 272.09 KB).
Murray and Murrumbidgee
Detailed information on how water is shared in the regulated Murrumbidgee and Murray valleys in NSW is provided in the factsheets below.
- How water is shared in the Murrumbidgee Valley (PDF, 528.62 KB)
- How water is shared in the NSW Murray Valley (PDF, 593.83 KB)
Supplementary water, formerly known as off-allocation water, is effectively surplus flow that cannot be captured, or ‘re-regulated’, into storages. When storm events result in flows that cannot be captured (regulated) in storage structures such as dams or weirs for future use, and the water is not needed to meet current demands or commitments, then it is considered surplus to requirements. Regulated rivers become unregulated for a period of time.
As soon as these conditions are identified for a particular river, a period of Supplementary Access is announced and details of the river reaches and time periods for supplementary access are published. Supplementary Water Access Licence holders can only pump water against these licences during these announced periods. Other categories of licence holders can choose to pump water during these periods as usual.
Those holding General Security Water Access Licences may, under some circumstances, pump water 'without debit' during these periods. For more information on pumping during supplementary flow events go to the relevant water sharing plan.
Supplementary flow events can occur in any regulated system at any time and therefore access is purely opportunistic. Supplementary events depend on the amount and location of rainfall and ensuing streamflow, and the catchment conditions at the time. They can be triggered overnight and last for a day or two, a month to six months or more, depending on the river system and nature of the flow event.