Tech Tales: New tsunami gauge for Christchurch

Published: Fri May 14 2021 2:30 PM

Following years of planning and preparation, Christchurch’s new tsunami gauge at the New Brighton Pier has been installed.

The old Sumner sensor site has been soldiering on despite being buried by large amounts of rock and debris that fell into the ocean during the 22 February 2011 M6.2 earthquake. We needed to replace the site because we can’t access it to service it.

It is impressive that the current gauge is still operational after all these years. Rocks that have been reworked by the ocean around the Christchurch coastline have broken up and washed ashore, burying our current gauge’s protective covering.

What our tsunami gauges look like- the Sumner sensor is buried under metres of rock

What our tsunami gauges look like- the Sumner sensor is buried under metres of rock

Our tsunami gauge data is collected by two pressure sensors at each site so that we have a backup in case one fails. They need to be regularly maintained, and we haven’t been able to do this for the current site for years. We are unsure of the remaining lifespan of the current sensors, and so the need to choose a new site was important for our tsunami monitoring network.

New Brighton Pier, Christchurch – our new tsunami monitoring site

New Brighton Pier, Christchurch – our new tsunami monitoring site

New Brighton Pier was chosen as the new site location for many favourable reasons, including its distance from the shore (where it will be immune to rock build up), its useful exposed location to record a tsunami, ease of access to service the equipment, and the desire to maintain tsunami monitoring capabilities in Christchurch.

The tsunami gauge uses pressure sensors and measures sea level variations by comparing pressures at the surface with atmospheric pressure and calculating a water height. It confirms the occurrence of a tsunami and can help to forecast and alert other regions of what they might expect. It is designed to capture a large level change over a short timeframe.

We will continue to run the old site for several months to line up data with the new site, ensuring a continual stream of Christchurch tsunami gauge reporting.

The install was similar to other wharf sites we’ve built before, but each site has its challenges. A lot of design work went into planning the brackets (that were specially rolled to fit the pier leg) and steel pipe that houses the cabling. We also had to run the cables the whole 300m length of the pier back to the control box in the New Brighton library.

Field technicians, abseilers and divers working hard to build the site

Field technicians, abseilers and divers working hard to build the site

Due to the challenging location, we employed the help of abseilers and divers to complete the install. They worked brilliantly to get the site installed in just two days, and it is expected to be fully operational in the next week or so.

The site is part of the LINZ network of 18 tsunami gauge sites around New Zealand’s coast. GNS Science maintains and monitors these sites, and reports their data on the GeoNet website.

New Zealand tsunami gauge network

Attributable to: Kris O’Brien – GNS Science Remote Infrastructure Operations Coordinator

Media enquiries: media@gns.cri.nz or 021 574 541