Newsroom Special Inquiry

Drowning dreams: Apartment block where the waters meet

One of three recent coastal developments in the Coromandel Peninsula studied by Newsroom, an approved three-storey, 73-apartment building at 82 Richmond St in Thames risks flooding after sea level rise

In November 2016 Richmond Villas retirement village applied to build a three-storey block containing 25 one-bedroom and 48 two-bedroom apartments on the Thames shore. The apartments will extend the existing retirement village next door, and council had already said yes to building some additional units (though fewer in number, and they hadn’t been built yet).

The council’s planners decided that the effects of allowing more apartments, in a different layout, would not be significant.

And, while the site was already a known flooding risk, the district’s rules said the developer had to make the floor levels at least 4.1m above sea level to compensate, which the council felt was safe enough to mitigate the risk.

In making its decisions the council referred to an engineering report from 2001, when the retirement village was first proposed. Tonkin and Taylor, the developer’s engineering consultants, had concluded the flood risk was minimal, noting that “recent studies indicate a rise in sea level due to global warming of 0.49m by 2100”.

Images from Waikato Regional Council's coastal inundation tool showing flooding after 1/100-year flood

Sixteen years later, the council did not ask the applicant for an up-to-date flood and sea level assessment before approving 73 new apartments on the land. “While I recognise that present tsunami, river, coastal inundation and climate change modelling has altered in the intervening years, there is a significant scale of existing development within the site,” said the planning officer’s decision giving the apartments approval.

“The coastal defence seawall has already been constructed and is considered to provide a level of acceptable risk in respect of natural hazards, given the majority of the development has already occurred…” he said.

“The proposed design will ensure the minimum floor level is at least 4.10m [and] that will enable any flood water to convey beneath the structures during extreme events.”

Thames lawyer Denis Tegg was concerned about the flood risk. Specifically, he was worried about the cost and wasted money if the apartments turned out to be in a flood zone decades or even more than a century from now.

Tegg looked at the area using Waikato Regional Council’s coastal inundation tool – an online simulator that anyone can use to see what areas might be at risk from climate change.

He plugged in various flood levels and saw that if the maximum storm tide coincided with the maximum high tide, much of the site looked like it would be underwater after 0.8m of sea level rise. After 1.9m of sea level rise, the whole site looked like it would be flooded.

Tegg wrote to the council asking it to reconsider. The council replied in November, 2017 saying the site was zoned for intensive development, and that the district plan limited what criteria its officers could consider. “None of the criteria … relate to site suitability in respect of sea level rise and/or flooding,” it said.

Further up the Thames waterfront, a seawall acts as a barrier between the ocean and residential properties. Photo: Joe Dowling 

We asked the regional council’s flood expert, Rick Liefting, what would be a realistic extreme tide for the area, to plug into the simulator. While a maximum storm tide could happen at the same time as a maximum high tide (giving a flood level of 3.2m), he suggested using the lower 1/100 year flood level, which is 2.4m for Thames.

Using that storm tide level, the coastal inundation tool suggests that after 0.5m of sea level rise a storm surge could dampen the property’s edges.

After 1m of sea level rise, the property would be dry but the apartments would be surrounded by flooded houses and residential streets.

After 2m, the same storm surge would submerge much of the land and reach higher (by 0.3m) than the minimum height of the ground floor.

As for the tool’s accuracy, Liefting says it tends to overestimate real flooding, because in real floods friction and other effects slow water down. On the other hand, the simulation does not include waves, which might push real flooding higher. The tool is intended only as a heads-up, to prompt anyone who is concerned to get an accurate, site-specific assessment.

That hasn’t happened for this property since 2001, at least not in a form that the council’s decision on the site records.

The developer, Richmond Villas, did not want to comment.

Read more: Billions at stake as govt mulls sea level rules

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