Controlled releases from Blowering Dam are expected to ensure the Tumut River remains in flood for at least another four to seven days, WaterNSW CEO David Harris said on a visit to Tumut last Friday.
The releases are designed to free up airspace in the dam, which currently sits at 97.7 per cent.
Tumut received more than 25mm of rain on Sunday night and into Monday morning, raising the flow of Goobarragandra River. Releases from Blowering were wound back to accommodate the rain event, but the river is tipped to remain at or above the minor flood level for perhaps the next week, meaning the Riverglade Caravan Park will continue to remain closed and other affected regions will continue to be saturated.
Mr Harris said they plan on reducing the release rate out of Blowering Dam as soon as possible.
“The current plan, subject of course to rain, is that we would run at around the release rate we’re running at the moment (17,000 megalitres a day) to get that airspace up to 80 to 100 gigalitres, and then we’ll progressively cut back to a more normal release rate that will enable the reopening of the caravan park and so on,” he said.
“We have the positive side of reducing the peak height, however, it does prolong the duration of the flood event.”
WaterNSW are responsible for Blowering Dam, which manages inflows from Snowy Hydro further upstream.
Mr Harris said WaterNSW has been constrained by limits on how many gigalitres they are able to release per day according to regulators.
Blowering Dam was releasing 17,000 megalistres a day last week, above the channel capacity level of 9,300 megalitres prescribed in the Water Sharing Plan set down by the NSW Office of Water.
He said that limit of 9,300 megalitres should be raised in order to allow Blowering Dam to clear up airspace faster in the lead-up to a flood event.
“After our last event roughly a week ago we’ve been able to clear about 7 per cent of airspace in Burrinjuck Dam,” he said on Friday.
“We haven’t been able to do that here in Blowering, in part because of what’s coming from the top of the hill, and in part because of channel capacity constraints that exist through the town of Tumut.
“What we’re trying to ascertain is, what is the level that we can release out of the dam in a day, under normal operations, that will not have an impact on residents and businesses?
“My gut feeling is that it will fit somewhere around 13 to 14 gigalitres a day, but it’s certainly a lot higher than the current regulatory restrictions so we’ll be mapping that out. After this event, we’ll be sitting down with council and SES with a view to having that constraint raised somewhat so that we have greater capability in events like this.”
Snowy Valleys Council Interim General Manager Bob Stewart said there is plenty of room to free up the limited amount of gigalitres WaterNSW is allowed to release from Blowering Dam.
“[The current 9.3 gigalitres allowed is] well within the banks. There is certainly on top of that 9.3 some capacity,” he said.
Mr Harris said raising the channel capacity regulations would potentially give WaterNSW more leeway to avoid flooding events such as this one.
In the meantime, The Bureau of Meteorology is predicting more rain this Monday and Tuesday, following on from a stormy night on Sunday.
Mr Harris thanked the local council, SES, and local farmers and businesses for their understanding during this flooding event.