Another flood watch for Tumut River

Burrinjuck Dam.

A flood watch for minor flooding of the Tumut River has been issued.

The Bureau of Meteorology says moderate rainfall associated with a cold front has the potential to cause local and riverine flooding along the Tumut River over the weekend.

Catchments are relatively wet from recent rainfall.

Flooding may occur from Saturday as the weather system moves east.

It’s the fourth flood watch to be issued for the Tumut River since February. Minor flooding occurred last month.

WaterNSW announced yesterday it would be extending its airspace operations at Burrinjuck Dam to maximise storage capacity to capture inflows anticipated from rain forecast by the Bureau of Meteorology for the weekend.

Airspace releases, which have been underway at Burrinjuck dam since early July, have reduced the dam storage to 98 per cent of capacity today, with releases rising to 18 GL/day.

Those releases are planned to be reduced to minimum levels starting today in anticipation of weekend rain and the likely increase in downstream tributary flows which are already generating high river levels.

Since June 1 Burrinjuck dam has received more than 378GL on inflows, of which 190 GL have been released.

Blowering Dam sits at 97 per cent of capacity and is making minimal releases (0.5GL/day), having received 309 GL since 1 June, of which 209 GL has been released.

WaterNSW executive manager of system operations, Adrian Langdon said based on weather forecasts from the Bureau of Meteorology WaterNSW has released 15% of total storage capacity in Murrumbidgee dams in the past seven weeks to manage storage levels.

“Strict rules govern flood mitigation pre-releases. Pre-releases can only occur within a window of high confidence that the weather forecast is accurate, usually only days from the predicted rain event.

“A rain event sufficient to warrant pre-releases is also likely to create tributary flow impacts downstream, which could be exacerbated by poorly timed dam releases.

“The other key factor is confidence that the rain event will generate sufficient inflows to replace water released for airspace. Severe droughts have clearly demonstrated the critical importance of water security to the communities and economies serviced by our major supply dams.”

Mr Langdon said to date both Murrumbidgee dams have been able to capture large inflows and hold the water back to allow for downstream tributary flows peak.

“Conventional wisdom has it that all the water in the river originates from the dam, but this overlooks the major contribution of downstream tributaries.

“Dams reduce the impact of potential flood events by capturing peak inflows, and then releasing that water gradually once uncontrolled tributary flows downstream of the dam have themselves peaked and are subsiding.

“Without Burrinjuck and Blowering to capture the extensive inflows of recent weeks from its upstream catchment the Murrumbidgee valley would already be experiencing flooding.”