Frequently asked questions

The available water determination (AWD) for Namoi supplementary water access licences was reduced at the commencement of the 2024/25 water year to 0.42ML/share. This AWD applies to all supplementary water access licence holders in the Namoi. The AWD defines the maximum volume that can be taken in that year prior to trades and is normally 1ML/share. However, the access to allocated water is subject to periods of declared supplementary flow.

The reduced allocation is required to address non-compliance with the long-term extraction limit (LTEL). Note in other plans this limit is referred to as the long-term average annual extraction limit (LTAAEL). The Water Sharing Plan for the Upper Namoi and Lower Namoi Regulated River Water Sources specifies how this limit is calculated, how compliance is assessed and what action is required if there is non-compliance.

Growth in farm infrastructure has resulted in growth in total diversions. The water sharing plans specify triggers for when this growth needs to be acted upon; generally, when total diversions exceed the limit by more than 3%. This trigger has been exceeded in the Namoi. The current water sharing plan 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 LTEL. 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. See “What are the likely impacts?” for further information.

The assessment of growth has been based on the Namoi Source model. Results from this model were first published under the healthy floodplains program. See Model Scenarios Report (PDF, 742.37 KB). Since publication of that report, we have continued to make improvements to the model. This led to an updated compliance assessment which was published on our website in 2023. See LTAAEL compliance results | Water (nsw.gov.au). This assessment showed non-compliance and action was taken 1 July 2023 as per the requirements of the water sharing plan. An updated assessment has been completed and this again shows non-compliance; this assessment will be published on our website as soon as possible.

Licensing of floodplain harvesting will address growth in floodplain harvesting above the limit (based on water use development that existed in 1999/2000). We will revise the compliance assessment after the commencement of these licences and publish an updated AWD if changes to allocations are required.

Our current information indicates that it is likely that restrictions on supplementary access AWDs can be relaxed after floodplain harvesting licences commence but will still need to be less than 1 ML/share. This is because floodplain harvesting licences will not address growth in total diversions. Current model results show that there will still be growth in supplementary access diversions after floodplain harvesting licences commence resulting in non-compliance.

There is no guarantee that the supplementary access AWD volume can be taken, 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. 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. Instead, it 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. The figure below uses historic usage data to show which years would have had impacts if the reduced AWD was in place. The orange bars show years that would have been affected.

Note that at the time of writing there was very little supplementary access usage recorded in the 2023/24 water year in the Lower Namoi hence it is possible that there was no or little impact from the reduced AWD made at 1 July 2023.

We can't predict what the actual impact will be in the 2024/25 water year as we don't know what the supplementary access opportunities will be.

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 limit by comparing a model which reflects the limit to a model which reflects current conditions.

The models allow us to test what impact changes in infrastructure, rules or behaviour have on long term water use. Where we have metered water use, this is used to compare to the model. For LTEL compliance, what matters is that the valley scale total water use is reasonably reflected over multiple years; we don’t expect the model to match every year and we don’t expect the model to perfectly reflect each individual farm.

Simple tests for trend in metered use are not sufficient to assess for compliance with the LTEL. This is because unmetered water use is not included and also because the growth in use assessment method needs to take into account how permitted take would vary given climate, water availability and water sharing plan rules. This variation can be complex. There is not a simple relationship between rainfall or flow and the expected permitted use in that year. For example, in a wet period there might be less metered water use as rainfall and unmetered use such as floodplain harvesting fulfil needs to a greater extent. Going into a dry period, there might be large amounts of metered water use if headwater storages have good supplies.

We have assessed growth by representing changes in the valley. The most significant change that drives the growth is increased infrastructure. For example, on farm storage capacity has grown by over 50% since 1994 which the Cap is based on. Further information on infrastructure changes can be found in the Model Scenarios Report (PDF, 742.37 KB).