13 February 2011

Seqwater to undertake Wivenhoe Dam release with Twin Bridges, Colleges Crossing and Savages Crossing to be flooded: Should this have happened months ago?

Minister for Natural Resources, Mines and Energy and Minister for Trade

The Honourable Stephen Robertson


Seqwater to undertake dam release

13 February 2011

Seqwater intends to reduce the Wivenhoe Dam level for the remainder of the wet season, given the extreme floods in January and the current water security of South East Queensland.

Seqwater has formally recommended Wivenhoe Dam's be temporarily reduced to 75 per cent of its current Full Supply Level and expects to implement the release strategy gradually during the next week.

The Minister for Natural Resources, Stephen Robertson, said the release was recommended by Seqwater after its recent hydrology analysis and was a precaution given the second strongest La Nina pattern in history continues to influence the current wet season.

"Seqwater made its recommendation recognising the extreme January 2011 event that left the catchments soaked and the water tables full,'' Mr Robertson said.

"While we can't be certain about what rain is yet to come in this wet season, this measure reflects an abundance of caution.

"Seqwater has advised that a reduction in Wivenhoe's Dam storage level to 75 per cent of its Full Supply Level provides appreciable flood mitigation benefits ahead of any major rain events in the remainder of the wet season.''

SEQ Water Grid manager Chief Executive Officer Barry Dennien said he had advised Seqwater a reduction to 75 per cent would be manageable from a water security perspective.

Mr Dennien said the January floods also transformed our long-term water storage capacity with the recently completed Wyaralong Dam now full five years earlier than expected and now storing 103,000 megalitres which is able to be connected to the Water Grid when required.

"With Wyaralong full, other dams full around the region and the Grid in place, Wivenhoe Dam can be operated at a lower level for the rest of the wet season without impacting on water security,'' Mr Dennien said.

Seqwater Chief Executive Peter Borrows said Seqwater expected to implement the release later this week to reduce the drinking water storage capacity of Wivenhoe Dam from 1,165 million megalitres down to around 874 million megalitres.

"We are likely to begin the transition by next weekend, with a slow release rate over about nine days discharging around 30,000 megalitres each day,'' he said.

"We will adjust the release to take into account any rainfall and tides as usual and this slow release will ensure no significant downstream impacts.''

Mr Borrows said that like other low volume releases in the past, there will be a limited number of bridges immediately downstream of Wivenhoe (Twin Bridges, Colleges Crossing and Savages Crossing) which will be closed during the period.

Mr Robertson said Seqwater's operational decision reflected current circumstances rather than issues which likely to be considered by the Commission of Inquiry into the recent floods.

"As per its terms of reference, the Commission of Inquiry will continue to assess dam operations during the January flood event and whether any changes to the long term framework are required,'' Mr Robertson said.

Mr Borrows said the dam would be maintained at 75 per cent of the current Full Supply Level until April, after the end of the wet season.

About Wivenhoe Dam

Wivenhoe Dam was built in 1985 to provide flood protection for South East Queensland after the devastation of the 1974 floods .

About 40 per cent of the dam's capacity is devoted to storing drinking water and the remaining 60 per cent is for flood mitigation. The dam is said to be at 100 per cent full supply level when the drinking water component is full.

The strategy and requirements for operating the dam, including flood mitigation and water releases, are outlined in the Dam Operations Manual. This Manual was developed in 1992. Since then it has been revised six times, most recently in January 2010.

The Manual is approved by the State's Dam Safety Regulator, in accordance with the Water Supply Act 2008.

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