A new sea-level gauge has been installed at Port Tauranga as part of a national network of gauges for monitoring tidal waves.
The Tauranga gauge is the fifth in a planned network of gauges to be completed by 2010 at 20 sites around the country, including five on islands.
Land Information New Zealand (LINZ) is overseeing the project in partnership with GNS Science, which is installing the network.
The gauge in Tauranga is attached to an underwater pile on a tug boat berth to measure changes in water pressure which relate directly to the wave height above the instruments.
``Gauges at coastal locations such as Tauranga will detect first landfall of tsunami waves,'' said aeme Blick, LINZ's manager of geodesy (Earth measurement).
They should also enable an ``all-clear'' to be given if a large undersea earthquake has not produced a tsunami, or only a small sea surge.
Instruments on islands such as Raoul, Macquarie and Norfolk will give information about the size and possible arrival times of incoming tsunamis from distance sources, sending data to GNS Science in Lower Hutt.
Geonet project director Ken Gledhill, said the sea-level gauges are important to the unami monitoring system which uses seismology, sea-level measurements, computer modelling, and historical information on seafloor earthquakes.
Seafloor earthquakes are the most common trigger for tsunami, but they can also be caused by undersea landslides or volcanic eruptions, and meteorite impacts.
New Zealand has experienced about 10 tsunamis higher than 5m since 1840, most of them arriving within minutes of seafloor quakes not far off the coast.
GNS scientists say a trigger in New Zealand could be a moderate (magnitude 6.5 or greater) earthquake within 200km of the coast.