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Investigating the aftermath of landslides

3D mapping to fight river risks in New Zealand

RUSHING to the scene of a dramatic landslide in helicopters and jetboats in a remote part of New Zealand might sound like a scene from an action movie - but it’s just a day at work for Physical Geography lecturer Dr Simon Cook.

Along with colleagues from Queen Mary University of London and Massey University, Simon flew out to Lake Wakatipu, in Queensland, New Zealand, to investigate the aftermath of a landslip in the Dart Valley.

The spectacular landscape of the Dart Valley has been used as the location for hit films including Lord of the Rings and X-Men, and is also popular with hikers because of its world-famous trails.

But the landslide blocked the Dart River, which created a 4km-long lake that flooded a walking track that is regularly used by tourists.

Diverting danger

Although the river did manage to find a way round the landslip – averting a potentially catastrophic build-up and burst of water from behind the dam – Dr Cook and his colleagues are now looking at how people, settlements and infrastructure downstream of the landslip could be affected as the landslip sediment is reworked and transported by the Dart River.

They are using the latest technology to investigate whether the sediment is likely to simply disperse, or whether it will move as a “sediment wave” towards the delta where the Dart River enters Lake Wakatipu. The way in which the sediment moves downstream, and the timescale for such movement, is poorly understood, but requires urgent investigation for a number of reasons.

Firstly, the riverbed in settlements that border the Dart River could suddenly start to build-up as the sediment moves through, meaning that flood defences offer less protection. Furthermore, the sudden loading of extra sediment onto the Dart delta could be sufficient to cause the delta to collapse, causing a tsunami which would be dangerous for towns on the lake edge.

The team are building a 3D model of the river using stereo-imagery from a camera mounted on a helicopter. The stereo-imagery requires targets laid-out on the ground with a precise GPS location. As the river is mostly inaccessible by foot, they are using jetboats and helicopters as transport.

High-tech mapping

Once the 3D model is completed, they will compare it with another made in 12 months’ time to see how it has changed.

The work has been funded by a Natural Environment Research Council (NERC) urgency grant.

Dr Cook said: “This is a problem that could happen in many mountainous environments, be it New Zealand, Switzerland or Nepal. We want to know how this sediment will move, and how long it will take – it could take months, years, decades, centuries – we really don’t know! But it’s important we find out in this case because of the associated hazards to residents and tourists in the area.

“The very few studies that have focused on this issue so far have been mathematical or have used simple scale models. To catch a real landslide in the act and have the technology available to monitor it is much less usual.”

Monday, 16th June 2014