Quake could cause massive flooding on Taieri

Gavin Palmer
Gavin Palmer

A large earthquake would likely compromise the Waipori floodbank and result in a flood akin to the 1980 disaster in an area including the airport, a new report says.

This is one of many findings of a Tonkin and Taylor report, released this week, commissioned by the Otago Regional Council.

It included a stability and integrity assessment of 214km of scheme floodbanks on the Lower Taieri and Lower Clutha flood plains, and in Alexandra.

The report noted most parts of the scheme were in good condition.

However, it urged urgent work at the Riverside Rd spillway at Taieri Mouth and outlined necessary work at the Waipori and Silverstream pumping stations.

Regional council engineering, hazards and science director Gavin Palmer said the council was working now on some recommendations and others were being put in its draft long-term plan.

In general the council was pleased with the report which said flood protection schemes were ''overall in good condition'', Dr Palmer said.

''I think it's telling it like it is. It shouldn't come as a surprise. Flood protection schemes reduce the risk but never eliminate it and there are some matters that need to be attended to.''

A difficulty the council faced was parts of the schemes were old and had been developed over time, he said.

''Some of the methods that have been used aren't the methods you would use today.''

The July flood last year supplied the council with a lot of information on how its schemes would work in such an event, he said.

A regional council report, drawing from the Tonkin and Taylor report, mentions the floodbank at the Waipori pumping station would be compromised in a large earthquake.

''A failure of the Waipori floodbank would result in flooding of West Taieri similar to the June 1980 floods. The area includes Dunedin International Airport.

''As such, ORC is developing appropriate contingency plans.''

A Dunedin Airport spokeswoman could not provide comment on the report yesterday.

The Tonkin and Taylor report urgently recommended work be done on the Riverside Rd spillway structure.

This included abutment repairs, crest repairs to ensure appropriate rock protection and the establishment of grass on the crest of the structure.

The council report noted the failure of the spillway would severely compromise the operation of the Lower Taieri Flood Protection Scheme in both east and west Taieri.

''It would also potentially cause sudden and catastrophic flooding of the upper pond.''

The council made allowance in the draft long-term plan for performance and integrity reviews of the spillway and strengthening works which would likely be required.

''In the interim, repairs will be necessary following any significant future overtopping events.''

The Tonkin and Taylor report outlined five necessary infrastructure or safety improvements required at the Silverstream Pumping Station.

The council report said failure of the Silverstream right floodbank at the station would compromise the performance of the scheme and potentially lead to failure of further floodbanks.

The Tonkin and Taylor report also noted maintenance issues, the council report said.

''Most relate to ongoing management issues such as stock damage, vehicle crossings and trees in close proximity to floodbanks. Staff are already investigating and actioning some of these issues and the remainder will be inspected and progressed according to priority.''

The council report outlines $2.14 million in floodbank integrity work projects planned for the next three years.

jono.edwards@odt.co.nz

 

Comments

Of course there's alwas the possibility that a decent quake will raise the Taieri plane a meter or two ...

 

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