Update on the Dart Valley landslide
Date: 6th January 2014
Update on the Dart Valley landslide.
On Monday morning staff from GNS Science and Queenstown DoC completed another inspection of the major landslide within the Dart Valley. It was observed that while a new lake had formed upstream of the landslide, the Dart River was no longer blocked as the water had begun to flow past the landslide debris. GNS considers there is no immediate danger of a large volume of water being suddenly released down the Dart River below the dam produced by the landslide.
The landslide and lake have cut walking access through the Dart Valley. DoC has been forced to close the Dart Valley Track between Daleys Flat Hut and Bedford Steam. DoC Conservation Services Manager John Roberts says “the area is now impassable, many sections of the track are either underwater or are undercut and have fallen away”. John explains “as the lake is not likely to disappear quickly this track closure will remain in place until further notice. Tramping the complete Rees-Dart circuit is therefore not feasible.”
“Trampers can still walk the Rees Valley to Dart and Daleys Flat Huts. However they will need to return the way they came, or exit via the Matukituki Valley. From the Dart Valley road end, people may walk from Chinaman’s Bluff to as far as Bedford Stream before returning.” John cautions “if you use any section of the Dart Valley Track, track please abide by all safety notices, and do not proceed into closed areas.” DoC is currently working to find an alternative route around the landslide and lake so the entire Dart Valley track may be re-opened. All other tramping tracks in the area remain open.
The QLDC harbour master advises that people wishing to boat, kayak or camp by the Dart River may do so but must stay alert for any changes in conditions. The public may find information on Dart Valley rainfall and river flow on the Otago Regional Council’s Waterinfo website www.orc.govt.nz/Information-and-Services/Water.
The new landslide has formed within an existing zone of instability located in the Te Koroka / Slip Stream area. While there have been other landslides in this vicinity, recent rainstorms have resulted in this more significant debris flow to cross right across the valley floor. In some places the debris is several hundred metres wide.
The new lake is forming behind the landslide. This lake is now over 3km long, spanning the full width of the Dart valley, and is up to 20 metres deep. The Dart River flows through this lake before exiting across the landslide debris and back into its usual course. The force of water is pushing hard across the eastern (true left) side of the valley, and the slopes here are being actively eroded. The lake is expected to only slowly subside as the river erodes through the landslide debris.
Until more is known of the long term consequences of the landslide the situation will be monitored closely and the public advised if conditions change.