Thames-Coromandel sea level rise: Council told it could be faster than thought

A presenter says sea levels could rise much more quickly than Thames Coromandel District Council data shows. Photo / File

A presentation to the Thames-Coromandel District Council has suggested that the district could be experiencing sea level rise at a rate three times faster than previously thought.

Katina Conomos, an independent consultant, presented to the council on the topic of sea level rise at a recent Audit and Risk Committee meeting.

She discussed data released by NZ SeaRise, a five-year programme to study and predict sea level rise in New Zealand, in early May this year.

The programme is funded by the Ministry of Business, Innovation and Employment from 2018-2023.

Conomos said the NZ SeaRise had found that "parts of Thames will likely experience triple the rate of sea level rise compared to the projections disclosed to the public".

She said it highlighted the issue of land subsidence, which could accelerate sea level rise.

She cited NZ SeaRise's case study of Thames, where it was said that parts of the area were "subsiding quite fast, at a rate of 10mm a year, because the suburb was built on reclaimed land in the 1970s".

NZ SeaRise claimed this "more than triples the rate and amount of sea- evel rise this area is experiencing".

She cited the council's information to the public, which claimed it will be 24 years before sea levels rise 20cm, and 40 years before they rise 40cm.

"It's a known issue, and yet it hasn't been factored into the Shoreline Management Plan."

She also said evidence from the Parliamentary Commissioner for the Environment had not been accounted for.

Thames-Coromandel District Mayor Sandra Goudie confronted Katina Conomos over her assertions. Photo / NZME

This said sea level rise increases the "frequency, duration, and extent" of coastal flooding - the commissioner found 30cm of sea level rise can cause once in 100-year events every four years.

She said the omission of both these datasets "misrepresents the extent of risk posed to our communities", which she said would leave residents "grossly under prepared".

She said the council's public meetings for feedback on the Shoreline Management Plan do not include the known impact of land subsidence.

"My concern is that we don't have that data yet to have an accurate picture [of sea level rise].

"I'd like to be proven wrong, I really would."

Councillor Tony Fox responded to Conomos' presentation by saying the management plan was "not necessarily a very precise document, because some things have changed in very recent times".

"What we do know is ... somebody has to do something.

"What we're saying is, in 20 years' time we need to get ready for that much [indicating 20cm], but it may be in 10 years' time.

"So I don't think it's neglected ... it is now being thought about, it has been understood for as long as I've been around."

Mayor Sandra Goudie questioned whether Conomos would agree that this is "theoretical sort of modelling, and that we need ... a bit more of a timeframe to see which direction things are going?"

Conomos emphasised that she was "not an expert in coastal science".

"I think what it does show is that we need to understand this better."

Goudie responded that she would "take that as a yes, then".

She then asked if she would agree that "council have been ahead of the game in beginning this process three years ago?"

Conomos said, "Respectfully, I wouldn't agree."

She felt being ahead of the game would have required "commissioning site-specific studies where we have known issues - and subsidence is a known issue within this area".

Goudie concluded her questions with "I just applaud what Tony was saying".

A final round of public meetings was held in Te Puru, Colville, Tairua and Whangamatā at the weekend as part of the Shoreline Management Plan project.

The council says the plan will set the relative sea level rise thresholds that will trigger adaptation responses, which includes sea level change that results from vertical land movements, such as subsidence.