Safeguard may cost us $56m

It could cost up to $56 million to protect central Whangarei from flooding.Protecting central Whangarei from catastrophic flooding could cost up to $56 million, but doing nothing could cost the city many millions more.
Whangarei District Council has been working on a flood management strategy for the central business district for the past two years and is about to go out for public feedback on six possible options to prevent the city getting flooded.
The options range from surrounding the CBD with two-metre high floodwalls to restricting future development in the flood routes and helping property owners to raise their floor levels.
The costs of the options range from $22 million to $56 million, but Deputy Mayor Phil Halse said flood damage from a 100-year storm event to the central city could cost $69 million and would increase to between $84 million and $150 million if climate change predictions come true.
Four times in the past 50 years - May 1956, March 1988, April 1995 and April 1999 - the CBD has been deluged by flood waters and the vulnerability of Whangarei's central city area was graphically illustrated when only a series of lucky breaks prevented the area again being flooded during the March 29 storm this year.
On that occasion the deluge caused the evacuation of central Whangarei and inundated up to 200 homes in the city, but the district could have been hit far harder.
The Whau Valley Dam, which stores most of Whangarei's water supplies, was only about 70 percent full on the morning of March 29. This allowed 550 million litres of runoff to be captured in the dam. Had the dam been full, it would have gone into the Waiarohia Stream and through the central city, causing a one-in-50-year scenario and up to $75 million of damage.
Mr Halse said the council is not willing to leave things to luck and over the next two months wants feedback on the flood management options. He said anything more than a 1-in-10-year storm combined with a high tide would be very nasty for the CBD.
"Every person in Whangarei District, and possibly the Northland region, benefits from the commercial and cultural activity generated by the CBD. We all have a stake in its protection," Mr Halse said.
"We really do need to work with the community to make some decisions on flood management. Although we have come through March and July relatively unscathed, that will not always be the situation. Our combination of rivers, rain catchments and the tide put us at risk."
The flood management report, produced by URS New Zealand, says more severe and more frequent flooding is likely under climate change scenarios.
The URS report proposes six options to reduce flood damage. They range from two-metre high floodwalls to restricting future development in flood routes and helping property owners to raise their floor levels. Indicative costs of the options range from $22 million to $56 million.
Public consultation will start next month when information about the flood risk and the possible solutions will be distributed, including at a public information meeting on September 6 in the Council Chamber. The new council will make any decision on which option to go with.