Tsunami risks going on LIMs

Tsunami risks will be added to thousands more Christchurch property records after new modelling showed flooding could reach further inland than previously thought.

New modelling of where the water may reach has prompted an extension of the city’s evacuation zones. The information will be added to publicly-available Land Information Memorandums (LIMs).

The new zones are based on tsunami modelling by GNS Science and the National Institute of Water and Atmospheric Research (NIWA) generated by earthquakes greater than magnitude 9 off the coasts of South and Central America, on the Kermadec and Hikurangi subduction zones and elsewhere around the Pacific Ocean.

‘‘[It] was based on conservative, worstcase scenarios and shows there is potential for flooding further inland than previously envisaged,’’ Christchurch City Council acting head of Civil Defence and Emergency Management Rebecca Newton said.

Meanwhile, Banks Peninsula is next in line for an evacuation zone review, once computer modelling of tsunami scenarios for that area is finished.

In Christchurch, there are red, orange and yellow evacuation zones.

The new modelling adds about 12,600 households to existing orange and yellow tsunami evacuation zones (about 23,300 properties in total).

The Christchurch City Council will add evacuation zone information to an additional 7000-odd LIMs, taking it to a total of about 18,000, a spokeswoman said.

People who are in the red or orange evacuation zones should head immediately to the nearest high ground or inland if they feel a long or strong earthquake, are told to by Civil Defence, or if they hear tsunami sirens.

The yellow evacuation zone could potentially flood in a large tsunami. People in this zone should evacuate if told to do so.

People in areas outside the tsunami evacuation zones do not need to evacuate in a long or strong earthquake.

‘‘If you live or work in an evacuation zone, you should have an evacuation plan in place.

Zone changes

Red zone:

The red evacuation zone is largely unchanged from 2017. It includes all beaches, tidal reaches of the Waimakariri, Avon, Heathcote and smaller rivers, Brooklands Lagoon and the AvonHeathcote Estuary. The Styx River is not included. The only changes from 2017 are extensions up the Avon River (Antigua footbridge), Heathcote River (Sloan Tce) and Waimakariri River (3.5 km upstream of Lorimas Rd/4.25 km downstream of the power pylons and the Waimakariri Regional Park at McLeans Forest). Orange zone:

The revised orange zone is significantly larger than it was in 2017. Much of this area is parkland, farmland or the residential red zone. There are about 9300 households (up from 5500 in 2017) and 23,500 residents (up from 13,500) in the 2019 orange zone. The whole of New Brighton, South New Brighton and Southshore remains in the orange zone.

Yellow zone:

The revised yellow zone is significantly larger than in 2017, but is only expected to be used for a tsunami with a wave above 5 metres in height, for which there would be warning of two to more than 12 hours. There are about 14,000 households (up from 5200 in 2017) and 37,500 residents (up from 13,700) in the yellow zone. This zone has been extended north of the Avon River in Burwood towards and across QEII Drive, and extended west and south to include parts of Dallington, Avonside (mostly residential red zone), Wainoni and Aranui.

‘‘Talk to your family, neighbours and work colleagues about where you would go and which route you would take,’’ Newton said.

‘‘An emergency can happen at any time so you need to be prepared.’’

In a report prepared for Environment Canterbury on the modelling, senior scientist Helen Jack said the tsunami evacuation zones were not tsunami hazard zones, nor tsunami risk zones, nor tsunami inundation zones. Rather they were areas people should evacuate as a precaution.