There are a variety of strategies that water users can use to secure water into the following irrigation season. This guide provides you with an overview of carryover in the southern Murray-Darling Basin and all the information you need to make an informed decision when carrying over water either against your own entitlement or through a contractual arrangement.
- In all systems, allocation can only be carried over if you own or have access to entitlement
- In the southern NSW systems, water can only be carried over against General Security (GS) entitlement
- Allocation can be carried over against High (HR) and Low Reliability (LR) entitlement in Victoria
- The South Australian government determines whether water can be carried over on an annual basis
- Carryover can be accessed through various water products
- There are risks associated with carrying over water including spill and availability
- Contact H2OX to discuss your carryover options
In the southern NSW systems, no storage or evaporation losses are incurred when carrying over allocation.
Carryover is available to General Security (GS) entitlement holders in the NSW Murray system. NSW Murray entitlement owners can carryover over up to 50% of their GS entitlement volume ie 50ML of allocation can be carried over against 100ML of GS entitlement.
Whilst up to 50% can be carried over, spill losses will occur when the volume of allocation in the account (carryover plus seasonal determinations) exceed 110% of the GS entitlement. Should determinations against NSW Murray GS entitlement reach 100%, any carryover greater than 10% will be forfeited.
Carryover is available to GS entitlement holders in the Murrumbidgee system. Murrumbidgee entitlement owners can carryover over up to 30% of their GS entitlements ie 30ML of allocation can be carried over against 100ML of GS entitlement.
Murrumbidgee carryover is constrained by the 100% rule, which prevents an entitlement owner accessing more than 100% of their entitlement volume (carryover plus seasonal determinations) in a single year. Should determinations against Murrumbidgee GS entitlement reach 100%, any allocation carried over will be forfeited.
Carryover is available to all watershare holders in the Murray, Goulburn and Campaspe systems. The general principle of carryover in these systems is that unused water can be stored in available airspace in a storage, but cannot displace additional storage inflows.
Entitlement owners in the Murray, Goulburn and Campaspe systems can carryover up to 100% of their High (HR) and Low Reliability (LR) ie 150ML of allocation can be carried over in an Allocation Bank Account (ABA) that has 100ML of HR and 50ML of LR entitlement.
The water authority deducts 5% of the carried over volume at the beginning of the irrigation season to cover evaporative losses from the storages. All carryover (less the 5%) is credited into the irrigators ABA on 1 July.
Any volume of water (from carryover and seasonal determinations) in the ABA exceeding 100% of the watershare volume is quarantined in the Spillable Water Account (SWA). The ABA holder is unable to access allocation in the SWA until a Low Risk of Spill declaration is made by the Northern Victoria Resource Manager (NVRM). A declaration means the probability of a storage spilling for the remainder of the year is below 10%.
While allocations are in the SWA they are at risk of spilling. A spill event can be a physical spill from a storage as is the case for Lake Eildon for Goulburn and Lake Eppalock for Campaspe. A physical spill can occur when the storage manager makes pre-releases from a storage to mitigate projected inflows or flooding as well as a storage exceeding its capacity and overflowing.
Internal spills are also possible and can occur in the Hume Dam for Murray. A Hume Dam is a shared storage with NSW, if Victoria’s share of the storage is full addition inflows “spill” into NSW’s share of the storage.
Any water carried over against HR has a higher risk of spilling because it is the first to be allocated. LR provides the lowest risk when carrying over allocation as it is only allocated once HR is 100% and there is sufficient water in the storages to guarantee 100% against HR in the following irrigation season.
The diagrams below show a scenario of carrying over 50ML of allocation against 100ML of Victorian High Reliability entitlement using the Carryover Calculator. On 1 July the volume of carryover is reduced by 5%, leaving 47.5ML of allocation in the ABA (1).
If seasonal determinations are 50%, 50ML of allocation is added to the account. At this stage the account owner has 97.5ML of allocation which can be used or traded (2).
Assuming seasonal determinations increase by a further 30%, 27.5ML of allocation will be quarantined in the Spillable Water Account (SWA), regardless of whether the account owner has used or sold any allocation (3).
If the water authority determines there has been a spill event totalling 50% of the water held in all SWA’s, the volume of allocation in the SWA will be reduced by 13.75ML in this example (4). Note that water is deducted proportionally across all accounts.
Once a low risk of spill declaration is announced, the 13.75ML of allocation in the SWA is available for the account owner to use or trade (5).
Information on carryover in South Australia is available on the Department of Environment and Water web site. Changes are being implemented from the end of the 2018-19 irrigation season as described in a fact sheet. In summary;
- Carryover will only be available to SA Class 3 entitlement holders
- Will be made available when minimum opening allocations are less than 40% (forecast provided mid-April with first formal announcement mid-June)
- Will be a maximum of 20% of the entitlement volume
- An evaporative loss of 5% will be deducted at a bulk level (not against individual entitlement holders)
- The total volume of allocation and carryover available to entitlement holders will capped at 100%
In order to carryover allocation you need to have access to water entitlement either through ownership or contractual arrangements. There are a range of contractual arrangements for water market participants to carryover – see Leasing and Parking for more detailed information.