Tsunamis unlikely on Lake Tekapo
Scientists have concluded that there is a small chance an earthquake could create a tsunami on lakes in the Mackenzie Basin.
Further tsunami research modelling has been carried out by National Institute of Water and Atmospheric Research (Niwa) scientists on the Tekapo lake bed.
The research was discussed at a recent Tekapo Community Board (TCB) meeting.
Environment Canterbury (ECan) has a role in assessing natural hazards in the region, which assists councils with civil defence and land use planning functions.
The TCB said ECan had previously commissioned background work from GNS Science in 2015 to look at whether there was any potential for tsunami on the Mackenzie Basin lakes.
Following on from that, further work has been undertaken by Niwa studying the bed of Lake Tekapo, the TCB agenda states.
Scientists mapped the Tekapo lake bed and studying its sediments, to determine whether underwater landslides have happened in the past, and are using this information to determine whether tsunamis could be created
According to Niwa’s report, the likelihood of a tsunami at Lake Tekapo was still rare.
ECan scientist Helen Jack said the Niwa was more comprehensive than the 2015 report, which was more of a ‘‘desktop’’ assessment.
‘‘There have been no recorded tsunamis in the last 200 years or so. It’s a pretty unlikely event.
‘‘However, Niwa’s research shows it could reach as high as 5m on the lakeshore,’’ Jack said. ‘‘So it’s obviously a potential danger.’’ Lake Tekapo was chosen over other lakes such as Wakatipu, Wanaka, and Taupo, the report says.
Tekapo was chosen because it’s a good size and depth to easily survey, and because there is population and infrastructure at risk, the report says.
‘‘The good thing about this latest research is that it’s given us a much better idea of the potential size of a tsunami at some point on the lake.
‘‘It’s given us a reasonable scope. The data is a lot more robust, so it gives us more opportunities to plan.’’
Jack said ECan would talk to the Mackenzie District Council about putting signs up on popular spots on the lakeshore reminding people to move to higher ground in the event of an earthquake or tsunami.
‘‘The important message is that these events are rare, but in the off chance that a tsunami does occur in the lake, you don’t want to be on the lake beach.
‘‘The most likely trigger for a lake tsunami is an earthquake, so, like any coastal or lake area in New Zealand, if you feel a long or strong earthquake, move off the lake beach and to higher ground as soon as the shaking stops.’’
Niwa used an echo-sounder to map the Tekapo lake bed, as well as seismic reflection surveys.
‘‘They could use the information gathered to determine what sort of landslides there have been in the past,’’ Jack said.
The report says any tsunami in Lake Tekapo would be highly dependent on the lake level at the time, which has an operating range of almost nine metres.
Even if a tsunami in the lake does not flood land, it may still cause sloshing in the lake, and surges on the lake beach, so it is important people know they should stay away from the lake shore after a strong earthquake, the report says.
‘‘It’s disappointing the council has turned their back on a communitybacked local supplier. We are the only experienced local bike share in the city,’’ he said.
The council has been approached for comment over its decision. It is understood to still be in negotiations with at least one other supplier.
Henderson said the bike-share pilot had freely shared its information and research with the council, effectively laying the groundwork for a permanent scheme by showing it could work.
‘‘Without the Bike Share Project the city would not be considering a bikeshare system at all,’’ the organisation said in a message to supporters.
An indicative business case, included as part of the tender documents, said a permanent scheme would replace the pilot and build on its success.
The pilot launched in August 2015 after a crowd-funding campaign saw 450 businesses and individuals chip in $50,000. Spark joined as a naming sponsor.
"It's disappointing the council has turned their back on a community-backed local supplier." Christchurch Bike Share project manager Robert Henderson
The system comprised 32 bikes across six stations around the city. People used an app to unlock the bikes. The first half hour was free with a subsequent hourly rate of $4. By the end of May, it will all be taken down.
Henderson said the work had come at a personal cost. He had spent about 80 per cent of his time over the past five years on the project for little return, he said.
However, ‘‘seeing our research and data contained within the document disseminated by council testified that – if nothing else – we’ve proven the case for bike share locally.’’
Mayor Lianne Dalziel was an early supporter, jumping on within a week of the pilot starting. Over the two and a half years it ran, more than 20,000 rides were taken.
About 74 per cent of the rides were taken by locals for short trips. The pilot also ran a successful trial using Christchurchs public transport metrocard to access bikes.
It was not known who the preferred supplier was, or if one had been selected, however Henderson expressed concern it could be an overseas, dockless [a system with no stations] provider.