Flood risk study delays project

17:00, Aug 28 2014

It could be two years before the council approves a plan change for residential subdivisions in Renwick after rivers staff asked for time to research a potential flood risk.

At yesterday's regional planning and development committee meeting, council rivers and drainage engineering manager Geoff Dick said the land proposed for residential subdivision had been flooded in 1983 when the Wairau River broke its banks. He asked for time to study the impact of possible flooding of Gibsons Creek and other small waterways near the township before residential expansion intensified in a 57 hectare block north of Renwick township, known as the lower terrace area.

Recent analysis suggested water flow into Gibsons Creek during a big storm had the potential to be higher than previously assessed, Dick said.

"The likelihood of a big flood has been estimated as a one-in-50 year event but latest thinking is that the risk may be greater than that, given also that stormwater inflow into the creek may increase with growth in the Renwick township.

"We're trying to anticipate potential issues and resolve them before they become problems."

Council staff said the potential issues were not seen as an issue for existing houses as newer houses have had minimum floor levels set as a consent condition and older houses tended to have been built on the higher ground, above flood levels.


Although some work had been done to upgrade the channel of Gibsons Creek in the past decade, Dick said he could not yet be confident there was sufficient capacity to give the preferred level of flood protection for a built-up area.

"We need to take a responsible approach as we do not want to create potential evacuation issues for emergency services unnecessarily. Far better to get an accurate assessment of the risk and make any flood control improvements first, before housing goes in."

The "traditional" part of Renwick was built on a higher terrace area, Dick said, and it had not been flooded in 1983.

Councillor Cynthia Brooks said long-time Renwick residents referred to the area east of High St as "on the bank" and the lower terrace area as "under the bank".

Marlborough mayor Alistair Sowman said raising and investigating these issues was "what responsible councils did".

"Anticipating some potential risk going ahead, it would be absolutely remiss if we didn't address it." The investigation meant the council would not look at changing the land's zoning until the river study had been done.

However, Sowman said people could still apply for resource consent to build houses in the area, and every case would be considered on its merits.

Council planning staff said any professionals dealing with consent applications in this particular location were advised not to make assumption that immediate subdivision would be possible.

The Marlborough Express