As disruptive storms and major flooding events become more common, councils are looking at how to prepare for the impact of a changing climate.
A 1 percent annual exceedance probability in flood flow Nelson City - with 0.5m sea level rise. It would see the CDB and half the homes in The Wood inundated. Photo: Supplied / Nelson City Council
In the coastal city of Nelson, 4170 properties are likely to be affected by 1.5 metres of sea level rise by 2130.
The council is holding community meetings and asking residents what features in the city they most want to protect.
The Wood - a desirable low-lying suburb close to Nelson's city centre is facing a future that will see more coastal inundation and river flooding.
Residents want to know what the options are to protect their homes, and how long they have.
Environmental engineer Rob Bell said New Zealanders needed to prepare for more frequent and extreme weather events.
"As across all our low lying areas around New Zealand, we're going to have this flood sandwich, which is rising sea levels, more coastal flooding, and wave overtopping at one end of a suburb and at the other end of the suburb, increased river flooding from increased intensive rainfall."
Showing the flood flow of an annual exceedance probability event after 1.5m sea level rise in Nelson. Photo: Supplied / Nelson City Council
He said while there was uncertainty about the pace of sea level rise, it was only moving in one direction.
"There's a misconception that this is going to be very costly and can we afford it, which is partly true, but the other side of the coin is, in terms of if we're going to continue to have these constant flooding events, or erosion events, or river flooding events, they're going to be quite costly to mop up, clean up, to rebuild."
The council has released coastal flooding maps based on technical assessments done by Niwa.
Predicted Maitai River flooding in Nelson in 2130. Photo: Supplied / Nelson City Council
Council climate change manager Rachel Pemberton said it was seeking feedback from the community on what residents valued about living near the coast and the Maitai River.
"We are hearing a lot of feedback on the importance of the natural environment, the importance of healthy habitats.
"People are talking a lot about recreational values so how they love living near Tahunanui Beach, for example, and they want to be able to continue having access to the beach and also people want to protect their coastal views and areas around the coast."
Council will then use the feedback to develop specific adaptation measures for different areas.
"Areas that are more vulnerable, such as Monaco and The Wood are likely to have prioritised adaptation options."
The Boathouse on Nelson's waterfront was damaged by Cyclone Fehi in early 2018. Photo: Supplied / Peter Moffatt
Stormwater and flood protection engineer Toby Kay said the region was exposed to coastal and river flooding hazards in different ways.
"Some of our coastline is very much exposed to wave run up or wave swell, for instance, along Rocks Road, Wakefield Quay and parts of Tāhunanui.
"In the CBD you have tidal inflow through the stormwater network, and it's more of a ponding type situation."
The new library site on the banks of the Maitai River with Nelson City Council's Civic House behind it. Photo: RNZ / Samantha Gee
He said there would be tradeoffs between different adaptation options: measures like flood walls, tidal gates, river diversions or detention ponds.
"The options need to be identified and prioritised based on what the communities value around the city and those values may be different in different areas, some people may put more emphasis on protection against flooding, and others may put more emphasis on protecting the environment."
The council is waiting for the Climate Adaptation Act and the National Adaptation Plan to be released by government later this year before it plans any specific mitigation measures for the city.
The council is seeking feedback on Nelson's Climate Adaptation until 14 August 2022.