New lake blocks Dart River track

HUGE LANDSLIDE: A slip has blocked Dart River near Queenstown, forming a natural dam and causing flooding.
HUGE LANDSLIDE: A slip has blocked Dart River near Queenstown, forming a natural dam and causing flooding.

A landslide near Glenorchy has caused a 3km-long lake to form and cut off a walking track, but the Department of Conservation says no further hazards are likely.

The landslide into the upper reaches of the Dart River on Saturday, at Sandy Bluff, initially caused flooding at Dredge Flat.

DOC said the debris was several-hundred metres wide in some places.

The incident also caused a lake to be formed upstream from the slip. That lake is now more than 3 kilometres long and 20 metres deep.

GNS Science and the Geonet Response team, DOC and Queenstown Lakes District Council harbourmaster Marty Black assessed the extent of the slip and the area was extensively monitored by helicopter. Inspections revealed that a well-known landslide at Slip Stream was active in recent rainstorms, sending debris flows on to the valley floor.

A broad silt band was deposited in the Dart River area and a lake formed behind the band.

Yesterday the river was flowing over the newly formed silt band.

DOC conservation services manager John Roberts said the landslide and lake had cut walking access through the valley and that DOC closed the Dart Valley Track between Daleys Flat Hut and Bedford Stream.

"The area is now impassable, many sections of the track are either underwater or are undercut and have fallen away."

Mr Roberts said the lake would not disappear quickly so the track would remain closed.

The department was working to find an alternative route for trampers, he said.

Dart River Jet Safaris resumed trips yesterday after its operations were suspended because of the slip and Dart River Jet regional manager David Kennedy said that, while the main Dart River channel had changed direction at the point of the slip, this was normal activity for the river following heavy rainfalls.

"GNS, DOC, the harbourmaster and Dart River Jet are all confident that the lake that has formed will gradually lower, that no abnormally high flows will be experienced downstream, and that there are no additional hazards posed in the Dart River below the slip area," he said.

The Southland Times