Updated flood maps for Awanui and Kerikeri/Waipapa catchments

12 Jun 2020, 4:47 PM

Updated river flood maps for Awanui and Kerikeri/Waipapa catchments are now available online at www.nrc.govt.nz/naturalhazardsmaps

Rivers and Natural Hazards Manager Joseph Camuso says the revised maps are based on the very latest survey data available and the new modelling more accurately portrays food risk in the catchments.

“These constant improvements in data collection help us prioritise our work to protect the areas we know to be most at risk,” he says. “The reassessed results are shown clearly on the updated maps.”

Man with data equipment by the river.Regional council staff member Cory Lydford gathers data from the Awanui River last winter. In the background atop a newly-rebuilt stopbank behind the Te Ahu Centre is an official party whose members were surveying improvements to the Awanui flood scheme.

In the Awanui catchment, where the council has a comprehensive programme of flood protection work in progress, we have seen reduction in flood levels vs pre-scheme works.

“The council is in the second year of the eight-year $15 million Awanui flood risk reduction programme, so to see these results coming through already tells us we are very much on target with our work to reduce flood risk to Kaitāia township and its surrounding communities,” Mr Camuso says.

The programme, funded 70% from regional rates and 30% from local rates, includes a spillway upgrade to direct water away from the Bell’s Hill slip site, work on the lower Awanui River catchment, and stopbank stabilisation behind the Te Ahu centre.

The Kerikeri/Waipapa catchment modelling also shows reduced flood risk as a result of the upgraded data collection processes.

The models forecast the predicted impacts of 10-year, 50-year and 100-year floods and consider the latest Government climate change projections on storm rainfall intensity and sea level rise.

One of the main benefits of the flood maps is to reduce the future development risk from flooding. Because of this, we have incorporated an allowance for climate change following MfE guidelines of roughly 18% more rainfall and 0.5 metres of sea level rise by 2120.

The detailed survey data the flood maps are based on comes from river and floodplain areas, hydrology assessments of rainfall profiles, tidal conditions, river catchment conditions, and computer modelling of floods to determine the likely extent of flooding.

“The risk from floods relates mainly to the depth and spread of floodwater, although other issues like debris, localised high intensity rainfall, overland flows and extremely high tide levels can increase the potential risk,” Mr Camuso says.

The council’s Regional Policy Statement for Northland (2016) contains policies for managing land in flood hazard areas and district councils need to consider flood hazards in their district plans and when issuing building and resource consents.