Murrumbidgee Dams and Flood Mitigation

11 August 2022

Recent wet weather has seen major flows into the region's dams. In the past 12 months, Blowering and Burrinjuck dams have received more water than each storage can hold.

Much of this water has been safely released downstream by WaterNSW's dam operators through carefully managed airspace releases.

As Executive Manager - Operations, Ronan Magaharan told ABC Riverina's Sally Bryant this morning, since 1 July 2021, 'Blowering Dam has received more than 2,080 Gigalitres (GL) of inflow and released more than 2,120GL - more than the entire volume of the Blowering storage (1,630 GL) and Burrinjuck Dam has received more than 4,000GL inflows and released more than 3,980GL (over four times its capacity)'.

Flood operation objectives are to reduce releases during rainfall events, to allow downstream tributary inflows to pass before making releases from the storages, with the aim of reducing the flood peak downstream.

The flooding event last week saw inflows into Burrinjuck Dam and other downstream tributaries that far exceeded forecasts. However, careful management of Burrinjuck Dam in the week leading up to the event helped reduced downstream flood impacts, with airspace releases prior to the event lowering the Burrinjuck storage to below 90 per cent.

The airspace created enabled the dam to capture the peak of the inflows, before then releasing the water safely after the flood peaks had passed.

"These actions effectively cutting the flood peak at Gundagai in half," Ronan told Sally in this morning's interview.

"To have captured the entire flood event, the storage at Burrinjuck would have had to be at approximately 65 per cent.

"It is also important to note that while flooding may be occurring downstream of the dam, this is not necessarily caused solely by dam releases."

Similarly, Blowering and Burrinjuck dams are not dedicated flood mitigation dams; they are supply dams to support local communities and farmers for the long-term. However, WaterNSW operates them to provide as much attenuation to flooding where possible. It does so in consultation with the community and stakeholders who rely on these dams in both wet and dry times.

For the recent event, WaterNSW would have reduced the storages further, but despite making significant releases, the wet weather has prevented more airspace being made in a safe and responsible manner.

WaterNSW works in close contact with the SES to ensure that dam releases do not further exacerbating a flood impacted river system, and with the Bureau of Meteorology (BoM) to understand forecast rainfall and river conditions.

In terms of community consultation, currently in the Murrumbidgee, WaterNSW is running a local Airspace Reference Panel, key local stakeholders such as councils, SES, Police, irrigators groups and others who we engage with to advise and inform airspace targets.

While the BoM and the SES are responsible for flood warning communications, WaterNSW urges local landholders if they haven't done so already, to sign up for our Early Warning Network. This is a free service which gives you up-to-the-minute information on dam releases across the State. You can do that by visiting: www.waternsw.com.au/supply/ewnand signing up.

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