Porirua City Council today committed $17.9m to reduce the flooding risk for homes in the Karehana area of Plimmerton.

In November last year a significant localised downpour saw more than 50 homes in Plimmerton flooded, some for the second or third time in five years. Following the flooding Council launched a catchment-wide investigation to develop options to reduce the flooding risk. These options were presented to Council’s Te Puna Kōrero committee today to decide on a way forward, having also heard the views of the community.

In the investigation Wellington Water led a team of engineers in considering more than 20 potential infrastructure solutions, then refined and grouped these into three options packages.

Wellington Water’s recommended option delivers benefits to the majority of homes across the catchment, at a cost of $17.9m. It includes a pump station, stream upgrades to above Firth Rd, hydraulic improvements, pipe network diversion down Cluny Road, inlet protection and debris nets in the scenic reserve. It was recognised that even this level of investment won’t stop flooding in the catchment fully and that a handful of houses won’t get the level of desired protection.

While council officers suggested the work in the recommended option could be done in two stages, Porirua Mayor Anita Baker successfully moved an amendment to ensure the entire package of works went ahead as soon as possible.

"I’m here for the whole city, but for me this is about doing one job and doing it right. The impact on this community was devastating and we need to move as fast as we can on this."

Councillors Mike Duncan, Faafoi Seiuli and Moze Galo voted against the amendment, preferring to do the most urgent and impactful parts of the Karehana work immediately, and the rest in stages, in order to consider costs alongside flood protection work needed in other parts of the city.

The recommendation was carried and the project will now move into the detailed design phase.

Recognising the need for flood protection across the city, Council also committed to the development of a city-wide retreat policy, targeting the most vulnerable flood prone homes across Poririua, prioritising homes where there is a threat to health or safety, or frequent internal flooding.

Mayor Baker said while the Karehana catchment was assessed by flood modelling as the highest priority flood prone location in the city, there were other areas that needed addressing and these would not be forgotten.

"The city-wide retreat policy now being worked on will be considered early next year and will be designed to prioritise the homes most in need."

In other flood protection work underway across the city, there is $3m allocated in the Long-term Plan for improvements in Takapuwahia. The final stage of construction on the flood storage wetland in Elsdon Park is expected to be completed by May 2022. Investigations are also ongoing into flooding hotspots across the city including in Hongoeka, Maereroa School, and Kenepuru Drive.

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