New flood study for Mangatārere Stream

An updated study into flood prone areas near the Mangatārere Stream near Carterton has been released by Greater Wellington Regional Council which provides interim flood hazard information ahead of a detailed study to be completed in 2020.

"Although the flood information is preliminary, we thought it was important to make the community aware of it," says Greater Wellington Cllr Adrienne Staples.

"It's important for the district council and the community to have the latest data on the flood hazard presented by the stream. It's vital for decision making by the district council on regulation, land use and development and for people undertaking private developments.

"Greater Wellington and Carterton District Council's focus will be on advising people, recommending building floor levels and dissuading inappropriate development that could be at risk from flooding."

The maps arising from the flood study area finalise an earlier 2014 report for Greater Wellington by Opus International Consulting. They are based on a 1-in-100 year flood and include 20 percent increase to water flows due to climate change to the end of this century. They show developed areas in Carterton could be at risk, primarily along the Mangatārere Stream and old river channels which have flooded in the past.

"Naturally, some people will be concerned about their property being shown in the flood study area. We are sensitive to people's concerns, and will be sending out information to explain what the flood study area means and how it could affect them. We also want to involve the community in assessing the hazard in more detail in the next phase and I hope that people will take the opportunities to get involved," says Cllr Staples.

The work is a precursor to a full Flood Hazard Assessment and represents a sensible compromise that allows Greater Wellington and Carterton District Council to communicate the potential flood hazard while indicating there is further investigation to be undertaken.

The more detailed flood hazard assessment, which is included in Greater Wellington's 2018-28 draft Long Term Plan, is scheduled for completion by 2020. It will include: a detailed hydrological study, a hydraulic model (especially at bridges and know flood-prone areas) more survey work and a focus on flood risks in Carterton's urban area. The report will be peer reviewed and independently audited and subjected to community consultation and involvement.

Depending on the outcome of the flood hazard assessment, a Floodplain Management Plan will probably follow so that Greater Wellington, Carterton District Council and the community can agree how the flood risk should be managed.

Carterton District Council Planning and Regulatory Manager Dave Gittings welcomes the new flood study and notes the value it will have for the affected areas of the Carterton District.

"We are looking forward to working with Greater Wellington to move towards a more precise model which will ultimately introduce flood protection to minimise hazard to the community."

Dr Gittings says keeping the community involved is essential. 

 "It is important that our community are well aware of any potential flooding risks, and feel they have the opportunity to be involved in the process from the very beginning. We have the opportunity to work together at the conception of the study to ensure all parties are on the same page."

ENDS