WaterNSW is closely monitoring rising storage levels at the two major supply dams for the Murrumbidgee Valley, as the Bureau of Meteorology (BoM) forecasts ongoing wet conditions.
Burrinjuck Dam, on the Murrumbidgee River, was sitting at 103 per cent capacity as of 8 August 2022 up from 90.5 per cent on 2 August, having received a peak inflow of over 230GL/d on 4 August. Spillway releases are currently at 90GL/d, or about 60 per cent lower than 7 August’s peak inflow.
WaterNSW has worked with the BoM to monitor rainfall and flow forecasts, and made flood mitigation pre-releases from Burrinjuck Dam earlier in August. Releases were then able to be reduced to 500MLa day as the peak inflows arrived on 4 August. Recent flows in parts of the Yass River upstream of Burrinjuck Dam were the highest ever recorded.
Blowering Dam, on the Tumut River, which feeds into the Murrumbidgee, is currently sitting at 94.5 per cent capacity, up from 91.6 per cent on 2 August, currently on minimum release of 0.6GL/d.
Major tributary flows downstream of dams have also been a feature of recent rainfall, including large volumes flowing in the Jugiong and Tarcutta creeks, and to a lesser extent the Goobarragandra River.
WaterNSW’s river operations personnel are managing the Burrinjuck Dam spillway releases to lessen the impact at Gundagai and further downstream.
WaterNSW said it is closely collaborating with the BoM, which means it has access to Australia’s best weather forecasting. BoM is using that information to carefully manage flood pre-releases in the event of a significant rain forecast.
In a recent statement, a WaterNSW spokesperson said, “As dam managers, we are mindful that we cannot make releases to create airspace capacity to absorb inflows without a high degree of certainty that the anticipated inflows will replace those releases, and therefore not impact adversely on long term water security.”
“The other consideration is that we don’t want to exacerbate a flood-prone river system downstream of the dam by adding water to the existing, naturally occurring tributary flows, which make a major contribution during a flood event.
“Careful management of dam storage, airspace requirements and pre-releases are required, no more so than in the lead up to forecast significant rainfall events.
“Without Burrinjuck Dam to capture the extensive inflows of recent days from its upstream catchment the Murrumbidgee valley would be experiencing more significant flooding.”
