Commonwealth Environmental Water
What is meant by carryover of water?
NSW Rural Fire Service Media
Carryover is provided for in regulated parts of the Murray- Darling Basin and allows water users to hold water in storages so that it is available in subsequent years. Carryover provides water users with greater flexibility to manage their own water availability across years.
How is carryover governed?
The States have created rules that apply to the carryover of water. The rules manage the impact that water users may have on other users through their carryover decisions.
Commonwealth Environmental Water operates under the same rules and pays the fees and charges associated with its water as all other water licence holders. The Commonwealth can carry over water in the same way as occurred when the water entitlements were managed for agricultural use. So:
- Carryover was previously available to the water entitlements now held by Commonwealth Environmental Water and its acquisition for environmental purposes does not affect the maximum carryover in dams.
- Commonwealth Environmental Water, like any other water holder, cannot fill up dams to the exclusion of other water users.
Figure 1 depicts how continuous water accounting operates in Northern Victoria.
Continuous accounting occurs under water sharing plans in the Lachlan, lower Namoi, Gwydir and NSW Border Rivers. This arrangement is designed to provide for substantial carryover (100 to 200 per cent) because inflows are more variable than in the south of the Basin. Typically there are high maximum account limits which enable high levels of carryover. There are also annual use limits (100 to 125 per cent of entitlement). If the balance in a water account has reached the account limit then new allocations are no longer credited to that account. The total allocations that a user can receive, including Commonwealth Environmental Water, are limited by the space in their account.
In the Macquarie catchment there is a carryover limit of 100 per cent and an account limit of 200 per cent. If an entitlement holder held 150 per cent in their account at the end of the year than 50 per cent would be forfeited and may be re-allocated to others. These arrangements are similar to those applying to general security entitlements in the Murrumbidgee and NSW Murray where a carryover limit (of 30 per cent and 50 per cent respectively) applies. These arrangements apply equally to all users, including Commonwealth Environmental Water.
In some northern NSW catchments, water sharing plans provide for account or allocation "re-set" if a dam spill occurs. Under the water sharing plan for the Lachlan catchment, when Wyangala Dam spills, all general security access licence accounts are re-set to 136 per cent of entitlement irrespective of whether they held more or less water at the time of spill. Under the water sharing plan for the Macquarie, when Burrendong dams spills, all high and general security allocations are re-set to 100 per cent. These arrangements apply to Commonwealth Environmental Water and all other users.
Commonwealth carryover in northern NSW
In 2011-12 many environmental requirements were met through natural high river flows and flooding. In very wet years, it makes sense to carryover some environmental water so that it is available in future years when it may be of more benefit. Commonwealth Environmental Water has carried water over into 2011-12, and will carry over water into 2012-13, in many northern NSW catchments because use in future years is likely to produce more environmental benefit than further use in years with very high river flows.
Whilst the carryover of Commonwealth environmental water into 2011-12 was higher proportionally in several northern NSW catchments than anywhere else in the Basin, it was relatively small when compared to the capacity of storages and the carryover of others. For example, in the Gwydir catchment, 64 gigalitres of Commonwealth environmental water was carried over in 2011-12, which was 19 per cent of the water carried over by all users, and less than five per cent of the volume of Copeton Dam. The largest volume of carryover in northern NSW in 2011-12 was in the Lachlan catchment, where 86 gigalitres of Commonwealth environmental water was carried over, which is less than seven per cent of the storage capacity in that catchment.
It is anticipated that there will be higher volumes of carryover of Commonwealth environmental water into 2012-13. This is consistent with the expected approach of other users as there have been large inflows into storages and therefore increases in allocations, whilst there has been relatively low water demand.
Carryover allows all users, including Commonwealth Environmental Water, to provide for future year environmental requirements when conditions turn drier.
Impacts of Commonwealth carryover on other water users
If as expected the Commonwealth was to carryover 350 gigalitres in northern NSW into 2012-13 then this would take up less than 6.5 per cent of the total combined storage capacity in the major storages of the Lachlan, Macquarie, Namoi, and Gwydir catchments, and the Border Rivers.
A carryover of this size would be consistent with the expected carryover of other water users, and would occur within the carryover rules set by the NSW Government. The Commonwealth cannot store water above its account limits in any catchment and if it is at the account limit then allocations that would otherwise have been allocated to the Commonwealth would be allocated to other users.
Commonwealth Environmental Water will report each year on the volume of water that has been carried over on each entitlement type held in the Basin. Over the longer term it is expected that the percentage of Commonwealth environmental water carried over will be similar to other water users - although like all water users it will vary from year to year.