Menindee Lakes flood review

WaterNSW routinely conducts a review of major flood operations and other incidents to ensure procedures are followed and to identify opportunities for improvement.

The review was initiated to understand:

• Whether WaterNSW systems, policies and procedures enabled WaterNSW to properly execute its functions over the course of the event.
• Whether WaterNSW actions helped to provide flood mitigation benefits for the local area.
• The quality and availability of inflow data and modelling, in particular, the inflows from unregulated tributaries.
• The effectiveness of WaterNSW’s engagement and communications with other agencies involved in the emergency response; and
• Opportunities to further enhance communications with the local community before and during the event.

The review incorporates input from the community and WaterNSW customers.

Our review included feedback from local stakeholders. For example in late June 2023 WaterNSW held community drop-in sessions in Menindee over two days to gather feedback, and continues to engage with the Menindee community.  Feedback was also collected from WaterNSW’s Customer Advisory Group.

We had a huge amount of data over many months to analyse and that took us some time - probably a bit longer than we might have liked, but we’re pleased to make the report public now.

We also had the report independently assessed by an external expert, and built in time for that.

WaterNSW routinely conducts a review of major flood operations and other incidents to ensure procedures are followed and to identify opportunities for improvement. Continued improvement is very important to us. It was also important that this report was subject to an independent expert peer review.

While the review itself was undertaken by WaterNSW, it was subject to an independent expert peer review before any recommendations were considered by the WaterNSW Board. Those findings are now publicly available.

The report was an internal WaterNSW review of our flood operations at Menindee Lakes.  We meet regularly with other agencies and some of the thinking from those discussions and feedback has been taken into account.

The review found there is an opportunity to improve the availability of streamflow data upstream of the lakes.

The number and location of river gauges created challenges for WaterNSW flood planning and operations during the flooding events, and a review of the gauging network is recommended.

We found that there were gaps in river data and information that would have been helpful during the floods.

Historical reports and analysis indicate that during past floods, inflows to Lake Wetherell have peaked at around 60% of the combined flows in the Main Channel at Wilcannia and the Talyawalka gauge at the Barrier Highway.

During the 2002-23 Darling River floods the combined gauges represented approximately 100% of the flows, far exceeding the previous expected ratio of 60% of the Wilcannia total flow peak.

While manual monitoring also took place (i.e. attending a site in person and performing a remote gauge reading), the widespread flooding made accessing some locations impossible.

The current design of the gauging network and subsequent uncertainties in assessing Menindee Lakes inflows had a bearing on the inflow modelling undertaken by WaterNSW.

The review does not cover the March 2023 fish death event, but rather the flooding that preceded it. The fish death event was comprehensively reviewed by the Office of the Chief Scientist and Engineer. WaterNSW’s submission to that Review is available on the Chief Scientist and Engineer website.

Following discussion (and feedback) on the report with Government agencies and the community, WaterNSW will work to implement the listed recommendations as soon as possible.