Flockton flood protection to cost $50m

LOIS CAIRNS
Last updated 11:00 27/03/2014
Tony Doyle carries Andy Kimber
IAIN MCGREGOR/FAIRFAX NZ

FLOCKTON BASIN: Warrington St in Mairehau is repeatedly flooded.

Opinion poll

Is $50 million a fair amount to spend on flood protection in Flockton?

Absolutely. Flockton residents have suffered enough.

It seems like a lot. Can't it be done for less?

No, leave the area to the elements and spend the money re-settling the residents.

Vote Result

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The Christchurch City Council is working on two possible options for reducing flooding in the Flockton basin but wants to talk to local residents before it decides which one to pursue.

"We have a lot of work to do with the community here. This is their homes, their streets,'' the council's land drainage operations manager Mike Gillooly said as he outlined the options to councillors.

Option one is estimated to cost $50 million and involves deepening and widening Dudley Creek. It would reduce the risk of flooding in around 550 homes.

Option two involves constructing a pump station and a gravity piped diversion and a limited upgrade of the waterway at a cost of around $53 million. It would provide flooding protection to around 490 homes.

Gillooly said both options had their advantages and disadvantages and the council would need to do more work on both and engage with the community before deciding which one to pursue.

Option one was likely to experience difficulties in gaining land access agreements and therefore could result in programme delays. It was less likely it could be implemented within a two-year time frame.

Potentially there were 115 properties for which access agreements would be required in order to undertake the watercourse upgrading work, as well as 29 private bridges that would need replacement. A major upgrade would also be required of the bridge at the Hills Rd/Shirley Rd intersection.

Gillooly said the watercourse upgrade works were significant with approximately 35,000 cubic metres of earth to be excavated and removed and approximately 3.5 kilometres of watercourse affected. A considerable portion of mature, significant and protected trees would also need to be removed.

"It will mean a wider waterway; it will mean a narrower street. It will mean a change to the streetscape,'' Gillooly said.

Option two had fewer land access and resource consent constraints and it was more likely it could be introduced within a two-year timeframe.

The council would only need access agreements for 70 properties, but it would need to buy land for a pump station and have access to construct the diversion across Shirley Boys High School. Only 7500 cubic metres of earth would need to be excavated and removed (around one-fifth of option 1) as only 1.75 kilometres of the watercourse would be affected.

Gillooly said prior to the earthquakes there were nine homes in the Flockton basin area at risk of flooding in a 1 in 10 year event; since the quakes that number had increased to 30. If option one was implemented that number would reduce to three, while under option two it would reduce to five.

Comparing the options, Gillooly said option two provided less "resilience" to storm events in excess of a "50-year return event" than option two, but it would provide greater resilience against the impacts of future earthquake activity.

Gillooly said further work was required to finalise the cost estimates for each option.

The remedial work proposed was partly covered by the horizontal infrastructure rebuild programme and was subject to the funding agreement between the Crown, the council and the New Zealand Transport Agency (NZTA).

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Councillors voted unanimously to begin engagement with the community about the two options and to get staff working with key stakeholders, the Canterbury Earthquake Recovery Authority, the Earthquake Commission, the Ministry of Business Innovation and Employment, and Environment Canterbury on the options and how they could their implementation could be speeded up.

Shirley-Papanui ward councillor Pauline Cotter said the approach the council was taking would help give the people in the Flockton area some surety.

Christchurch mayor Lianne Dalziel said there were pros and cons with both options and the decision on which one to pursue would not be straightforward.

"We are going to have to do a lot more thinking through... and hear what the community has to say,'' Dalziel said.

Today's decision though was a significant milestone as the council could now talk to the community about what was possible. 

Dalziel said the Flockton basin was just one a number of low-lying areas where the council might need to consider flood protection work but it was the top priority because of the magnitude of the problems that had been experienced there since the quakes.

The Flockton basin has expereinced severe flooding on three occasions since the quakes - in June and August 2013 and in March 2014.

COST BREAKDOWN

Option one

Construction $38m

Land access $6m

Project implementation $6m

Target cost $50m

Option two

Construction $43m

Land access $2m

Project implementation $8m

Target cost $53m

- The Press

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