A NSW Government website

How water is allocated

Frequently asked questions

Frequently asked questions about the reduced supplementary water access allocations in the Border Rivers and Gwydir.

Reduced supplementary water access allocations in Border Rivers and Gwydir 2021-22

We have created some answers to frequently asked questions about the reduced supplementary water access allocations.

What are the reductions in the Border Rivers and Gwydir and what impact will it have?

The available water determination (AWD) made for supplementary water access licences at the commencement of the 2021-22 water year will be reduced in the Border Rivers and Gwydir. This AWD defines the maximum volume that can be taken in that year prior to trades and is normally 1 megalitre (ML) per unit share. The reduced limits will apply to all supplementary water access licence holders in those valleys.

There is no guarantee that this volume can be taken however; as licence holders can only take water when a supplementary flow event is declared. This means that the maximum volume has no effect in the many years that have insufficient supplementary access opportunities for an entitlement holder to use their water and reach the limit. Therefore, we can't predict what the actual impact will be in the 2021-22 water year, as we don't know what the supplementary access opportunities will be.

Supplementary events are declared when flows exceed the requirements set out in water sharing plans - typically when all other water requirements have been met. The reduced AWD does not impact on how these events are declared; rather reduces the maximum potential volume that might otherwise have been taken in the water year. Trading of water can continue as usual. The reduced AWD will not have any impact on licence holders in years when there are few supplementary flow events declared and hence little opportunity to take the maximum annual limit.

Using historic usage data, we estimate that there is about a 40% chance that the reduced supplementary access AWD will impact on diversions in the Gwydir in any one year; in the Border Rivers there is about a 20% chance.

Allocations can be restored when a revised assessment shows a return to compliance with long-term average annual extraction limits.

Why is a reduced supplementary water allocation required?

As part of our obligations under NSW Water Sharing Plans (WSPs) and commitments under the Basin Plan, access to water must remain within a legal limit as outlined in the specific water sharing plan for each valley. This includes compliance with the long-term average annual extraction limit (LTAAEL).

Results from modelling published under the healthy floodplains program show that the Border Rivers and Gwydir regulated rivers have exceeded the LTAAEL and that compliance action is required. These exceedances are described in the model scenario reports published during the water sharing plan consultation and can be found on the website and through the following links:

Growth in farm infrastructure has resulted in growth in diversions. The WSPs specify triggers for when this growth needs to be acted upon; generally, when total diversions exceed the LTAAEL by more than 3%. This trigger has been exceeded in the regulated Border Rivers and Gwydir systems. Licensing of floodplain harvesting will largely address this growth in use. Until then, the current WSP provisions require that the compliance action is to reduce the maximum available water determination (AWD) made on 1 July for supplementary water access licences.

The required compliance action is to reduce total diversions to the LTAAEL. Modelling is needed to determine the required action as the AWD impacts actual supplementary access diversions differently each year based on flow conditions and capability to store water. In many years there is no impact at all.

If a reduction of more than 50% (0.5ML/share) for supplementary access licences is required, then this will be staged over two years, with the impact for the 2021-22 water year capped at 50%. Any remaining growth will be managed through a further reduction in allocations in the 2022-23 water year. This is consistent with the approach taken to manage LTAAEL compliance in all groundwater sources.

How do we assess compliance with the limits?

It is important to note that legal limits and our assessments against them are based on long term capability to take water. The way that we share water and check for compliance takes into account variable climatic conditions. This means that a growth in use management action can occur in wet or dry years. In any one year, water use can be above or below the long-term average limits. We assess compliance with the LTAAEL by checking for long term trends in water use. We do this by developing river system models which reflect current conditions and compare to the LTAAEL.

We have previously not completed LTAAEL compliance assessments for surface water systems due to a lack of data availability and resourcing. New and updated data sets collected through the Healthy Floodplains Project has allowed for a major model update that will enable LTAAEL compliance assessment to commence. The department is committed to the ongoing implementation of LTAAEL compliance assessments

How is LTAAEL compliance different to SDL compliance?

We use a different method to check for compliance with the sustainable diversion limit (SDL) under the Basin Plan framework. The SDL compliance method compares modelled or estimated allowable diversions for any one year, based on its observed climatic conditions to the actual diversions in that year.

A running total is kept of the differences between expected and actual take until the cumulative total exceeds a threshold, rather than comparing long term modelled outcomes as done for LTAAEL compliance. The two compliance assessment frameworks can support each other and they provide multiple lines of evidence for monitoring growth in use.

The two methods may result in different compliance conclusions at times. For example, water use in one year may be significantly higher than that predicted by the models used for SDL compliance assessments, however; in the following year this may be lower, indicating that diversions are within the required limits.

The LTAAEL compliance assessment is less affected by single year anomalies and was chosen by NSW having regard to the higher degree of variability in northern basin rivers compared to the southern connected system.

How often will we update our assessment for long-term average annual extraction limit (LTAAEL) compliance?

We will revise the compliance assessment after floodplain harvesting licences commence. With the disallowance of important enabling regulations for licensing and measurement of floodplain harvesting, the timeframes for implementation are uncertain. Despite this uncertainty, the NSW Government remains committed to the task of regulating floodplain harvesting to legal limits set out in NSW water sharing plans and the Basin Plan so that we can meet our legislative obligations, improve environmental and connectivity outcomes and provide clarity for all water users and the regulator.

The supplementary water access AWDs can likely be increased in the Border Rivers and Gwydir regulated rivers after the commencement of the floodplain harvesting framework in these valleys.

Department of Planning and Environment is committed to ongoing LTAAEL compliance assessments as our models are progressively upgraded and updated, including progressive adoption of the eWater Source modelling software and as new data sets become available. After this, Department of Planning and Environment is proposing to adopt a risk-based approach to deciding the extent and timing of model revisions.

More information on this approach will be made available on the website in due course.