Flooding protection could cost $13.6m

LOIS CAIRNS AND GLENN CONWAY
Last updated 14:55 12/05/2014
Flood prone homes

Map shows the most flood-prone homes in the Christchurch City Council area.

Mike Gillooly
Stacy Squires/Fairfax NZ
OPTIONS APLENTY: Council land drainage operations manager Mike Gillooly said "there's a lot of tools in the toolbox" when it comes to tackling flooding in Christchurch.
Heathcote River in flood April 29f
Joseph Johnson
VULNERABLE PROPERTIES: Christchurch City Council established a taskforce after repeated flooding in areas such as Heathcote, Woolston and the Flockton Basin.

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Mayoral taskforce on flooding report Technical report

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Flood-prone residents should "brace for a wet winter" as council's short-term solutions are unlikely to be in place for at least three months.

However, Labour leader David Cunliffe said the solutions needed to be acted on 'urgently' and called on the army to help.

Christchurch City Council's flooding taskforce today revealed protecting the 56 most vulnerable homes in Christchurch from flooding, in the short-term, could cost as much as $13.6 million.

The multi-million-dollar estimate is the result of two weeks examining what short-term options could be used to reduce the flooding risk.

Council land drainage operations manager Mike Gillooly said some of the solutions the taskforce had come up with needed to be tested so there were some pilot studies ahead.

"I know people are desperate for measures but there needs to be wisdom in the spend,'' he said.

Rolling those pilots out could take about three months.

Asked what comfort he could offer those in flood-prone homes as they headed into the winter, Gillooly said: " I think we need to brace ourselves; this is shaping up to be a wet winter. Sadly what we've seen is what we're going to get.''

Gillooly said the taskforce had identified 56 homes that had flooded twice or more since the earthquakes. They were the most vulnerable and had been assigned a level-one categorisation.

Another 451 homes that had suffered repeated flooding below floor level had been assigned a level-two categorisation, while 487 homes that had their access compromised by flooding had been grouped together into level three.

If the council wants to protect the 451 properties that suffered repeated flooding below floor level, it is likely to add another $7m to the bill. This would bring the total cost of the short-term protection measures to more than $20m.

The report states that Christchurch has experienced about six significant rain events since the earthquakes -  four of which have been in the first four months of this year. It added there were no significant floods between 1999 and 2012.

'CALL IN THE ARMY'

Labour leader David Cunliffe said the flooding taskforce's findings were "a start'' and should give some certainty to flood-affected residents.

Longer-term solutions were never going to be found in the two weeks the group had to commission the report, he said.

"The temporary measures identified in the report, including sandbagging and water-proofing, need to be acted on urgently. As I stated in my open letter to John Key, the use of the army to do some of this work would bring some much-needed extra hands.''

Cunliffe said although it is a "complex and on-going process'', the short-term options have been identified and it was now time for the Government to step in and with the city council "immediately assist where it can''.

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SHORT-TERM MEASURES MAY INCLUDE RELOCATIONS

The taskforce had examined a range of short-term measures to reduce the impact of regular flooding.

Options for large-scale physical works that could alleviate flooding in the long-term are being worked on, but they are likely to take several years to implement.

Councillors have given the taskforce until the end of the month to come up with a recommended programme of action for each catchment area. They want those programmes to include:

- A temporary pumping solution in the Flockton basin

- The repair of flap gates in the Avon and Heathcote rivers

- The dredging of the Heathcote River

- The removal of debris and an improved maintenance regime.

Options the taskforce have been looking at include house defence and local area schemes which benefit more than one home. Where neither of those options was practical, then short-term relocation of the household was also considered as an option.

Gillooly said house defence typically involved raising the house, tanking the house (waterproofing it just above the level of frequent flooding), bunding (either raised mounds or sandbags) or property re-grading to improve drainage of floodwaters away from the house.

"There's a lot of things we can do; there's a lot of tools in the toolbox.,'' said Gillooly said, noting the taskforce had already spent about $600,000 on temporary works to improve the stormwater drainage system.

Council environment committee chairman Cr Phil Clearwater said the taskforce had made a lot of progress "but there was still a lot of work to do''.

However further work is needed to assess which options were most acceptable to the community before final decisions were made.

To view the mayoral taskforce on flooding report click here, or to view the taskforce's technical report on temporary flood defence measures, click here.

BY THE NUMBERS

- 56 homes that have flooded twice or more

- 451 homes that have suffered some flooding below floor level

- 487 homes that have had access to their homes compromised by flooding

- Of 56 homes that have flooded twice or more, 28 are in the Flockton basin, one in the Heathcote Valley, 13 in the Woolston, Opawa and Lower Heathcote area, five in Little River, and nine in Lyttelton

- The Press

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