Boating resumes on Dart River
Commercial and recreational boating has resumed on the Dart River, following a major slip at Sandy Bluff at the weekend, with boaties being cautioned to be alert for debris and altered channels, even at low flows.
Scientists from GNS Science have been assessing the slip and associated hazards and have advised that there is no immediate danger that a large volume of water would be suddenly released down the Dart River below the dam produced by the landslide. Dr Simon Cox said this was because the landslide dam was broad and the gradient of the channel was low. Scientists did not anticipate any abnormally high flows below the dam, other than what would be expected with rain falling in the upper catchment
“In our view, the landslide-related debris flows and the lake pose no additional hazard on the lower Dart River below the dam, but the main area of the landslide should be avoided,” he said.
Below the dam, a large amount of sediment and wood debris was being washed down the river. The water would appear dirty as in a flood, despite the low-flow conditions. “Close to the landslide dam the river is cutting through forest and trees have been falling into the river,” Dr Cox said. “River users should expect changes in channel position, areas of soft quicksand-like sediment, wood and rock debris, and periods of anomalous and slow changes – both up and down with no apparent cause.”
Queenstown Harbourmaster Marty Black said that on the basis of the advice from GNS Science, people boating on the Dart River should stay alert for any changes in conditions. He recommended anyone considering taking a boat up the Dart River should check the flow rates recorded on the Otago Regional Council’s monitoring gauge, on-line at http://water.orc.govt.nz/WaterInfo/Site.aspx?s=HillocksFlow