Talking to public of natural hazards

The lower margins of Glenorchy showing inundation from Lake Wakatipu on November 19, 1999. Photo by ORC.
The lower margins of Glenorchy showing inundation from Lake Wakatipu on November 19, 1999. Photo by ORC.
The Otago Regional Council (ORC) will meet Glenorchy and Cardrona Valley residents soon to discuss concerns of increasing risk of exposure to surrounding natural hazards.

Reports from detailed ORC investigations carried out last year into the natural hazards in Glenorchy and the Cardrona Valley said as the populations and resulting demand for development increased, so too did residents' vulnerability to surrounding hazards.

"Places that have more things that can be affected can have higher risk," ORC environmental engineering and natural hazards director Gavin Palmer said.

Cardrona Valley residents were exposed to hazards including flooding, sedimentation and erosion.

The Glenorchy township was at risk of inundation from high lake levels, as in the November 1999 flood, as well as debris flows and flooding from the Buckler Burn, Bible Stream and the Rees and Dart rivers, the reports said. For both areas, mass movement and seismic hazards generated by earthquakes had the potential to affect residents and infrastructure, such as access routes, that the wider community depended upon.

Mr Palmer said the hazard studies would be presented soon at community meetings, although dates were still to be confirmed.

The Glenorchy and Cardrona Valley studies were part of a "planned programme of investigations of places where such information would be valuable", he said.

"The setting of both of these places is such that there are multiple hazards of varying degrees and there are people living there now and people going to live there ... it's about preparing information to help inform decisions by people about where and how they live ... that's primarily what the community meetings will be about."

Mr Palmer said the investigations also involved drawing together information that had been published previously and providing the public with an overview. For example, in Glenorchy, the Rees and Dart river deltas were gradually extending into Lake Wakatipu and research from the University of Canterbury was giving a better understanding of how the deltas would continue to change.

The reports noted climate changes could also affect the frequency and magnitude of flood hazards in the two communities.

"Other PhD work that's been undertaken for the ORC has shown that we can expect precipitation in the western part of Otago to increase and we've also been seeing a trend of an increasing level of Lake Wakatipu."

Providing information on communities' vulnerability to natural hazards was not just useful for residents and people who visited or operated businesses there, but also for territorial authorities which had to make planning decisions on land use, Mr Palmer said.

lucy.ibbotson@odt.co.nz