Analysis of new data raises Ohakune flood levels

Ruapehu District Council (RDC) is urging Ohakune residents not to be alarmed by Horizons new natural hazard mapping web portal that significantly increases the potential reach of extreme flood events.

RDC chief executive Peter Till said that the flood hazard information on the web portal has been updated using the latest data analysis from recent flood events.

“It is a fantastic tool but the information needs to be considered in context of the likelihood of a one in 200 hundred year flood event that the predictions are based on,” he said.

“A one in 200 hundred year flood predicts flood waters of up to a metre higher than previous predictions which were based on a one in 40 year flood event and are what was used for design purposes.”

“The move to one in 200 hundred year flood predictions reflects the availability of new data from recent flood events and the increasing public expectations for local government to plan for and mitigate these types of risk.”

Mr Till said that the flooding risk in the identified areas has been known about for many years however the much larger “at risk” area in the new hazard mapping may come as a surprise to many.

“Council is sensitive to the fact that the owners of properties that were not thought to be affected and that are now shown to be at risk in extreme flood events may now be very concerned.”

“As more detailed information and analysis becomes available it can from time-to-time throw up the odd unwanted surprise.”

“Over recent years we have been actively working to mitigate the effects of floods in Ohakune including; increasing the size of culverts, ensuring new developments are appropriately sited and keeping gravel and other obstructions such as garden ornaments and vegetation clear from water courses.”

Mr Till noted there are other options available such as diverting the streams running through town to run through rural areas and encouraging home owners to raise their house up.

“The Waimarino-Waiouru Community Board (WWCB) has previously been asked to consider diverting local streams however the idea was not progressed on the grounds of cost and effects on land owners,” he said.

“In the light of the new flood data analysis and higher flood levels these ideas may well have to be reconsidered.”

“Whatever mitigation steps are decided upon will impact on residents and property owners differently and come at a cost to Ohakune ratepayers.”

“As such more public discussion is required on what the best compromise for the township is.”

Mr Till said that council would be presenting a paper to the WWCB on the implications of Horizons new flood risk assessment at their next meeting on 1 October.

“This will be followed by a presentation to council by Horizons on 27 October.”

“Ohakune residents can expect to be consulted on possible mitigation actions early next year.”

The Horizons natural hazard mapping web portal can be found at: http://www.horizons.govt.nz/keeping-people-safe/emergency-management/regional-hazards/flood-plain-mapping/

Peter Till
Chief Executive

ENDS

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