Moanataiari residents to consider sea wall options
Published on 31 March 2023
A public meeting in Thames this week was well-attended by residents of Moanataiari, who were presented with preliminary options for upgrading the community’s protective sea wall.
Around 130 residents gathered in the Thames Civic Hall where they were updated on the five-year annual inspection and performance review of the Moanataiari Inundation Protection Scheme, or sea wall, conducted by engineering firm Tonkin and Taylor.
The review considered how well the wall is currently protecting the community, how future sea-level rise might affect the wall’s performance, and outlined options for longer term. It found the wall is currently performing well but may require upgrading to extend its lifespan beyond 2036 if the anticipated rate of sea-level rise continues.
Improvements to the sea wall are part of the adaptation pathway for Moanataiari that resulted from our Council’s three-year Shoreline Management project.
Longer-term, our Council and the community will need to have discussions about the possibility of managed retreat. These discussions will be informed by guidance from Government and its proposed Climate Change Adaptation Bill.
“We are maintaining the sea wall; that’s the commitment we’ve made. It’s a process we’ll work through together with the community to decide what that looks like,” our Mayor Len Salt told the meeting.
Options for the sea wall
Three options for upgrading the wall were presented at the meeting:
Option 1: Additional rock reinforcement and some increase to the existing timber parapet to improve resilience.
Option 2: An additional 1 metre high concreted wall to increase the lifespan of protection by around 30 – 40 years.
Option 3: A significant rebuild of the wall increasing the embankment height by 1.7 metres to provide for protection for approximately 100 years.
A preliminary business case estimate shows the costs range from:
- $200,000 - $500,000 for Option 1
- $2,000,000 - $4,000,000 for Option 2
- $13,000,000 to $27,000,000 for Option 3.
Without any improvements, sea water is likely to overtop the wall during a 1-in-100 year storm event by the year 2036.
“That’s not just wave splash, that means during a big event in 2036 there could be significant amounts of water coming over the wall due to expected sea-level rise,” explained project lead Amon Martin.
No decisions were made at the meeting on the community’s preferred option. Moanataiari residents are now in the process of forming a community group to co-ordinate their engagement with Council and provide feedback on the options.
Once a preferred option is selected, detailed design and costing work will be undertaken, and potential funding approaches explored.
Mayor Len emphasised that our Council was committed to working with Moanataiari residents and ensuring there was constructive dialogue and consultation on the area’s future.
“We’re in this together,” he said. This included ensuring regular maintenance of existing stormwater facilities was carried out, taking into account residents' local knowledge.
Anyone wanting to join the residents’ group can email: ourcoast@tcdc.govt.nz