Airport at risk of flooding

A significant flood on the Taieri Plain would extremely seemingly result in a “catastrophic” inundation of Dunedin Airport due to the poor situation of floodbanks, a report has discovered.

A Tonkin + Taylor Ltd report evaluating each the probabilities ageing floodbanks within the Taieri flood safety scheme would fail in a big flooding occasion and the implications of failure is to be mentioned at an Otago Regional Council assembly subsequent week.

The report rated two sections of the Waipori floodbank as “excessive” danger due to the very excessive chance that they might fail and the “catastrophic” penalties in the event that they did.

Such a breach may result in catastrophic harm to the terminal constructing at Dunedin Airport, inundate the runway and trigger main long-term disruption to the area.

The sections rated excessive equated to 400m of the 109km stretch of floodbanks, however 15% had been rated very excessive danger and 47% excessive danger.

Solely 7% had been rated low danger, and the remainder had been rated medium (31%).

The report was based mostly on the estimated performances of the floodbanks — elements of that are greater than a century outdated — in a flood occasion similar to the one in June 1980, which induced widespread devastation throughout the Taieri Plain and closed Dunedin Airport for 52 days.

Council workers estimated there was a 26% probability of such a flood occurring within the subsequent 30 years and a 40% probability within the subsequent 50 years, based mostly on in the present day’s local weather patterns.

Council engineering supervisor Michelle Mifflin mentioned as soon as workers grew to become conscious of the acute danger score for the 2 sections, they had been investigated instantly.

As a precedence, bushes rising close to the floodbanks affecting their integrity could be eliminated within the subsequent few months, which might require specialist gear and geotechnical recommendation on how the banks must be repaired.

“For the remaining dangers, a danger mitigation investigation is deliberate — triaged on the severity of their danger score.”

Mosgiel-Taieri Group Board chairman Andrew Simms mentioned the neighborhood had each proper to anticipate the regional council to make use of the charges it collected to guard life and property on the Taieri Plain.

“We can be making each effort to make sure that is a precedence for the Otago Regional Council.”

The board had had vital issues for a while about insufficient upkeep on the Silver Stream, Mill Creek and Owhiro Stream.

His preliminary response to the report was flood safety loomed as the most important concern for the neighborhood this yr.

“We’ve numerous issues and have raised these with the regional council all through 2023.

“This report now is just not doing something to allay our fears.”

Dunedin Airport operations and infrastructure basic supervisor Nick Rodger mentioned the report highlighted the vulnerabilities within the system of pumps, drains and floodbanks that protected the Taieri Plain.

“Dunedin Airport will proceed to work intently with ORC to cut back the general stage of danger from flooding, with this concern additionally being analysed by our flood hydrology plan, which may even examine web site stage mitigations within the occasion of a wider system failure.”

Ms Mifflin mentioned the council was planning to carry neighborhood info periods concerning the report. Dates had been to be confirmed and marketed.

Whereas the flood safety scheme did work to cut back the flood danger, the chance of floodbanks being overtopped or breached underneath flood circumstances may by no means be eradicated.

vaughan.elder@odt.co.nz