Flushing abandoned

Contact Energy called off plans to flush sediment from Lake Roxburgh on Thursday, after expected high flows in the Clutha River failed to eventuate. Heavy rain fell in the upper Clutha catchment area on Tuesday and Wednesday and the power company had hoped the river would rise enough to start the flushing operation, for the first time in several years.

Contact generation manager Graham Quinn said Contact dropped the level of Lake Roxburgh by 4m on Wednesday to prepare for flushing.

"By lowering the level of the lake, it speeds up the velocity of the water passing over it, and as it moves, it scours out the sediment and moves it downstream."

As part of its consents issued in 2005 to continue operating the Roxburgh and Clyde hydro dams, the company was required to reduce the volume of sediment in Lake Roxburgh and in the Manuherikia River to help mitigate the risk of flooding during high flows.

The river was expected to rise to more than 1300cumecs yesterday but the flow was closer to 850cumecs.

lynda.van.kempen@odt.co.nz