Kaikōura’s Sea Level Rise Sparks Warning To Council

Saturday, 8 June 2024, 6:20 pm
Article: David Hill - Local Democracy Reporter

The sea is rising faster than expected in Kaikōura, which could leave the coastal town vulnerable by 2040, the local council has heard.

Speaking at a recent council meeting, Kaikōura Water Zone Committee chair Ted Howard said measurements taken of sea level increases over the past few years were "a bit on the scary side".

However, a senior scientist has urged caution over the figures as measurements can vary significantly from year to year due to a number of factors.

The Kaikōura Water Zone Committee is a joint committee of Environment Canterbury and the Kaikōura District Council tasked with water management policy.

The 7.8 magnitude earthquake in 2016 raised Kaikōura’s coastline by two metres, buying the town 100 years against previous sea level predictions - or so it was thought, Mr Howard said.

This prediction was based on the measured sea level rise which averaged 2.6 millimetres a year between 2005 and 2015.

"The numbers just don’t quite stack up anymore," Mr Howard said.

‘‘Over the last 400 days, every day the ocean has been the hottest on record for that day," Mr Howard said.

‘‘When you look at the actual measured sea level rise, it is a bit on the scary side.’’

The measured sea level rise was 4.4mm in 2022 and 7.6mm in 2023, he said.

‘‘I am guessing this year it will be over 10mm,’’ Mr Howard said.

At this rate, the earthquake may have given Kaikōura 25 years reprieve rather than 100 years, meaning the town could be vulnerable by the late 2040s, he said.

But Environment Canterbury environmental science and hazards senior scientist Justin Cope urged caution as sea level measurements can vary from one year to the next.

‘‘Factors like seasonal differences, the climate and water temperature can cause the average sea level to vary significantly from year-to-year."

This can cause a variation of 100-200mm, he said.

To even out annual variability, sea level rise was assessed over longer periods, such as 50 years.

Mr Cope said prior to the earthquake, the Kaikōura coastline was sinking at a rate of around 3mm a year, which resulted in a "relative sea level rise" of around 5mm a year (3mm/year subsidence and 2mm/year sea level rise).

It was unclear what the long term impact of the earthquake would be, he said.

The latest predictions were for around 0.7 to one metre of global sea level rise over the next 100 years, depending on greenhouse gas emissions.

Should the Kaikōura coastline return to a level of 3mm per year of land subsidence, then ‘‘relative sea level rise’’ over the next century would increase to around 1.1 to 1.5 metres, Mr Cope said.

In his submission to the Kaikōura District Council’s Long Term Plan earlier this month, Mr Howard also highlighted the risks of the Kowhai River flooding and the alpine fault.

He called on the council to work closely with Environment Canterbury to reduce the risk of flooding in the town.

The 2016 earthquake dislodged two cubic metres of shingle at the head of the Kowhai River, which could be washed downstream in a major rain event ‘‘and it won’t be pretty’’, he said.

A magnitude 8 earthquake on the alpine fault could leave Kaikōura without electricity and isolated for several months, Mr Howard said.

Installing solar panelling at Mackles Bore on Mt Fyffe Road would help to secure the town’s drinking water supply.

Kaikōura District Council chief executive Will Doughty said Mr Howard had given the council plenty to think about.

‘‘These are issues we need to keep on the radar and be mindful of.’’

LDR is local body journalism co-funded by RNZ and NZ On Air.

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