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Report on findings of October 2023 flooding event released – Waitomo District Council

Waitomo District Council has released a report on the findings of the October rainfall event that caused significant flooding to the western side of Te Kūiti.

Received by Council on 28 November, the report provided a summary of the flooding event and the impact, and information on staged works to improve the resilience of the stormwater network.

It also identified potential budget implications for both the roading and water activity groups as a flag for future decision making.

The Te Kūiti West stormwater network was overwhelmed by a short period of intense and very localised rain on Sunday 8 October 2023, and repair and recovery works prioritised after the weather events earlier in the year were unable to alleviate damage to private property.

General Manager Infrastructure Services, Shyamal Ram says while the stormwater network couldn’t cope with the initial intensity of the event, once the rain slowed the drainage system was able to clear the majority of floodwater within 40 minutes except where stormwater had ponded on individual properties and was unable to flow away.

“Most of the stormwater network in Te Kūiti is designed for a two-year storm event, however it is accepted that weather patterns are changing and that these rain events will happen more frequently and with increased intensity.”

Several plans, both long-term and short-term, are being worked on to help restore, repair, and improve the resilience of the stormwater network. This will help reduce the impact of future weather events.

Seven critical sites in the western area of Te Kūiti have been identified and are now regularly monitored before and after a rainfall event.

Council staff have been very proactive in inspecting stormwater structures and pipes using CCTV, as well as cleaning critical sites.

“Since the January flood more funding has gone into stormwater improvements such as improving stormwater inlets and cesspits and will include installation of scruffy domes and wing walls, which will help with capturing the runoff and prevent debris from blocking a drain or outlet. These are the short-term measures,” says Shyamal.

“Council staff will also Investigate how surface flooding coming down from the western hills can be reduced or slowed.

“One option is to build retention ponds; however, further investigation is required. This will involve several and considerable steps such as identifying potential sites, working with landowners, seeking Regional Council resource consent, securing sufficient budget for the project, procurement and construction.

“A project to undertake modelling of the Te Kūiti stormwater system is also underway and will now be expanded. The modelling will identify where more significant works may be required such as

larger pipes or retention ponds. This will be a costly exercise and options will be considered based on budget and design.”

The capital cost of $240,000 to implement short-term measures has been approved for the financial year 2023/24, and will be planned for in Council’s Long Term Plan for 2024/25 and 2025/26. Another $471,000 of the roading budget will be used to upgrade the cesspits on the road to capture the runoff.

The work is expected to be carried out between February and May, subject to the weather and contractor availability.

The construction of longer-term solutions such as retention ponds and major stormwater pipe size increases have not been determined and are not included in the draft Long Term Plan.

A dedicated webpage ‘District Flooding Updates’ has been created to provide residents with useful information in one place. It includes a Frequently Asked Questions Fact Sheet and information on insurance claims. This page will be updated with news and information as appropriate. The full report on the findings can be found on this page as well.

www.waitomo.govt.nz/our-services/roads-water-waste/infrastructure-updates/district-flooding-updates/

 

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