Published originally by the Nelson Leader on 12 November 2020
by Jenny Easton
OPINION: Pre-emptive managed retreat is the best response to imminent sea level rise, experts told a meeting hosted by Engineering NZ and Te Kāhui Whaihanga NZ Institute of Architects (NZIA) in Nelson.
Four experts shared their views with an audience of 120 people last month on the question: ‘What are the options for the top of the south as sea levels rise?’
“The rate of sea level rise is accelerating. It will increase by another 30 cm by 2060,” said Nathan Edmondston, the Nelson/Marlborough NZIA branch chair.
“All buildings and infrastructure in low-lying areas will need to be relocated to higher ground before the sea claims them. So, instead of continuing to develop these areas, we need to start discussing alternatives now so we can come up with better strategies.”
He stated that a current council strategy of raising minimum floor levels for new buildings in low-lying areas is not a long-term solution, because insurance is likely to be withdrawn from at-risk areas and forthcoming managed retreat legislation may allow councils to stop upgrading key infrastructure in the coming decades.
A phased reduction in carbon budgets and reduced net energy availability will mean that we will soon need to replace emission-heavy materials (e.g., concrete and steel) with timber, he said.
Dr. Yuki Fukuda, from Zero Carbon Nelson Tasman, who presented jointly with Edmondston, showed that sea walls can give a false sense of security.
Japan’s largest sea wall (10 m high x 2.8 km long) was overtopped when the 2011 tsunami devastated the coastline. In fact, the death rate was much higher than in other towns without big sea walls. “The remaining community has now relocated 40-60 metres above sea level,” she said.
Greg Bennett, a stormwater engineer at Waimakariri District Council, also urged communities and councils not to try and battle the gods of sea and wind.
He observed that the $250,000 sea wall to protect Granity School was not doing well and that the school would have been better off being relocated to higher ground.
The NZ Coastal Policy Statement requires a 100 year timeframe, and that should be our target. As chair of the Coastal Restoration Trust of New Zealand Tahuna Ora, Greg advocated for the use of sand dunes and other natural coastal processes in a positive way, to retain the beaches as long as possible.
The guidebook includes examples of native dune plantings: https://www.coastalrestorationtrust.org.nz/resources/coastal-restoration-handbook/.
Dr. Chris Cameron, the climate champion for Nelson City Council, reminded the audience that climate change is already here, and sea level rise is like a slow tsunami.
We need to be planning for change so we can act deliberately and effectively, not react in haste, which is more expensive and traumatic, he said.
He will be designing a process for the region to work together on a long-term spatial plan, based on extended collaboration with communities. There will be protection options as well as managed retreat, with the four well beings (social, economic, environmental and cultural) always top of mind. He concluded that: “The best way to predict the future is to create it.”
The panel discussion was facilitated by Katrina Kidson who has a civil engineering background and is now a business coach, with active involvement in Sustainable Business Network and Businesses for Climate Action. Councils have started the process by asking for public input into their long term and strategic plans, and that will encourage them to go faster and further.
Stacey Fellows, an engineer with Fonterra, said that sea level rise is “a massive challenge so we need to be proactive, share solutions and not be overwhelmed by it.”
The video of the workshop is available here:
Jenny Easton is from Zero Carbon Nelson Tasman