Waipā updates flood maps to prepare for extreme rainfall event

Waipā District Council has updated its flood maps. Image / Supplied

Waipā District Council has released new flood maps for Cambridge, Te Awamutu, Pirongia and Ōhaupō highlighting the impact of an extreme 1-in-100-year rainfall event.

Although a rainfall event of this kind has a 1 per cent chance of happening every year and is expected to only occur once in a person's lifetime, the maps were developed by the council last year to understand natural hazards in the district.

Mayor Jim Mylchreest said the maps would help to ensure the council stormwater assets are fit-for-purpose.

"The map layers show where water will accumulate in an extreme rainfall event, which will help to identify areas in our existing stormwater network where further investigation may be required. By bringing these maps to the public, property owners will also be able ... [to] be better prepared in any eventuality."

The council's public flood hazard maps show areas of flooding in blue for present-day flooding as well as any future flooding because of climate change in purple. Flooding depths are not shown on the public map but are available upon request.

Mylchreest said owners of properties that were potentially at risk of over-habitable floor flooding in such a rainfall event received a letter with an individual property map showing the likely depth of the water.

"We recognise this may be a stressful time for those property owners and we are here to assist wherever we can ... We hope that this will help them be as prepared as possible."

Mylchreest said property owners who have not received notification from the council but can see their property covered fully or partially by a flood layer should not be alarmed.

"I can certainly understand any concern ... but we would like to make it clear that if you haven't received a letter, the flooding is minimal and unlikely to reach your dwelling's floor level. Where this occurs, it generally indicates very shallow water near the habitable dwelling or water pools outside the home, such as in garden low spots."

The council's current stormwater drainage system deals with frequent rainfall events, whereas the mapping represents an extreme rainfall they are not designed for.

Rivers and stream fluctuations and non-urban areas are not included in the maps, as this information is available from Waikato Regional Council.

• To view the public flood maps or to find out more click here.