Penny Smart, Kaipara constituency member on Northland Regional Council

Flood threat maps released

by Paul Campbell

Landowners in Kaipara and on Northland’s east coast, in Paparoa and at Waipu, have been issued with new Northland Regional Council maps showing the potential effect floods including large ‘one in a century’ type events could have.

The Regional Policy Statement for Northland contains policies for managing land in flood hazard areas and district councils need to consider flood hazard information when processing resource and building consents.

Landowners thinking about future building work on their land who want to know more about how the flood hazard maps may be applied should contact their district council.

“They need to ensure that decisions on what’s built, and where, is based on the best information available,” said Kaipara constituency councillor for NRC, Penny Smart.

“Over the next few days, the council will be writing to the roughly 600 landowners within the flood mapped areas outlining the latest flood risk to their properties and directing them to the new maps.”

She said council has been methodically working its way through the region, initially focussing on reducing flood risks in more than two dozen catchments deemed to be facing the highest flood threats. District councils have also produced some stormwater flood maps for specific settlements.

The two latest catchments have now also been modelled, which forecast the predicted impacts of a 10-year, 50-year and 100-year floods and take into account the latest government climate change projections on storm rainfall intensity and sea level rise.

“Technically, there’s a 10 per cent chance of 10-year flood happening in any year, a two per cent chance of a 50-year flood and a one per cent chance of a hundred-year flood over 12 months,” said Cr Smart.

“As with other parts of Northland, residents in both catchments are already familiar with heavy rainfall events and how these affect properties in their respective areas.

“The risk from floods relates mainly to the depth and speed of floodwater, although other issues like debris can increase the potential risk.

Additionally, factors such as localised high-intensity rainfall, overland flows and extremely high tide levels can also elevate the degree of risk.

“We’ve had a number of actual floods including in June 1997, March 2007 and January 2011, which have been very useful from a computer modelling point of view. We’ve been able to use these real-life experiences to validate some of our flood models.”

The new flood maps can be viewed via the regional council’s website nrc.govt.nz/naturalhazardsmaps.

Alternatively, landowners with questions about the maps or who want to provide the council with any additional information they have regarding flooding at their properties can contact the council’s Rivers Team on freephone 0800 002 004.