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Flood protection project targets vulnerable area of Nelson

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A multi-million dollar project that will increase the flood carrying capacity of the Maitai River between Hanby Park and Clouston Terrace will get underway this summer.

The most significant flood resilience project undertaken by Council since the Saxton Creek Upgrade, the work targets an area that saw some of the worst flooding during the August 2022 weather event.

This area of the Maitai is particularly vulnerable to flooding, with the existing stopbank at Clouston Terrace currently only capable of withstanding a 1:5 year flood event.

In August 2022, flooding affected properties between Nile Street, Mill Street and the stopbank.

“I have been involved with Civil Defence responses for 15 years. The flooding in this area in 2022 was some of the worst I have ever seen,” says Group Manager Infrastructure Alec Louverdis.

This project will reduce the risk of future flooding in the area in five ways, including:

  • New floodwalls
  • Upgrading the quality of existing stopbanks
  • Increasing the capacity of the river channel

On Tuesday 24 June, Council held a community meeting with affected residents to present the project plan for the Maitai between Hanby and Clouston.

“This is exciting for us from a technical point of view, but also for the solutions developed by our specialist engineering consultants Tonkin & Taylor,” says Alec.

“We were encouraged by the positive and supportive response from residents and we will keep in close contact throughout the work. All were keen for the work to start as soon as possible.”

Tonkin & Taylor looked out as far as 2130 and modelled solutions for a range of present day and future extreme weather scenarios. Their main focus was to maintain recreational access and the integrity of the river.

“Some solutions looked at potential property purchases but Tonkin and Taylor's innovative and practical design allows us to achieve the required outcomes without going down this avenue. The decision to take land from Hanby Park instead was a practical and compassionate solution and we’re really happy with the outcome.”

The summary of the proposed work includes:

  1. Lowering the level of the bank under the east bridge span creating more space under the bridge for pedestrians and cyclists.
  2. A 2m flood wall alongside the new pathway adjacent to Clouston Terrace, that will extend to chest height above the road carriageway.

“We are raising Clouston Terrace,” says Alec. “Clouston Terrace, which runs alongside this section of the river may be raised by over a metre, as a result we will need to reconfigure several property accessways. We will be working with residents for the best solution for each property.”

Once the project is complete, Council will work closely with residents to discuss options for enhancing the area, including opportunities for planting and artistic detailing of the concrete wall.

These finishing touches are an important way to reflect the character of the neighbourhood and involve the community in shaping the final look and feel of the space.

The project team recognise the importance of protecting the natural ecology both in and around the river.

A lizard survey found the protected northern grass skink inhabits the Maitai River banks within the works area.

Council has sought a Wildlife Act Authority permit from Department of Conservation to salvage the lizards and relocate them to the pest-free Brook Waimārama Sanctuary.

Along with the local lizards, the Maitai is considered as a ‘high’ value habitat with a diverse native fish community. In-river construction will be timed to avoid the spawning season for bullies and trout, and erosion and sediment control measures will be in place to protect water quality and instream habitat.

Where works in the water cannot be avoided, ecologists will capture and relocate fish away from the construction zone. Once completed the floodways will provide additional habitat for fish and planting will provide shade for fresh water species. For the local birds, works will be undertaken outside of bird breeding season where possible and bird nests will be checked prior to any removal of vegetation.

Four individual projects make up the wider Maitai Flood Resilience project. This overall project includes stormwater intake upgrade on Cleveland Terrace, river flood improvements from Hanby Park to Clouston Terrace, a flood wall upgrade and extension on Nile Street and at stormwater improvements at Queens Gardens for a total budget of $9 million, for which we are receiving $5.4 million from Central Government through the Regional Infrastructure Fund. This work will be carried out over the next two financial years and completed by July 2027.

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