The updated rainfall flood map showing the Taradale area in Napier. The light blue area denotes flooding up to 300mm, blue up to 500mm, and dark blue over 500mm. Photo / NCC
The updated rainfall flood map showing the Taradale area in Napier. The light blue area denotes flooding up to 300mm, blue up to 500mm, and dark blue over 500mm. Photo / NCC
Napier’s new rainfall flood maps will likely lead to more homes being built on piles, rather than the more commonplace concrete slabs, an architecture expert says.
Napier City Council recently released updated flood maps showing the properties at risk of flooding from heavy rainfall during a one-in-50-year event (2% annual exceedance probability).
The updated maps show 16,477 Napier properties are either fully or partially covered by a flood zone.
The depth of potential flooding varies for each impacted property but is as little as 100mm to more than 600mm.
Properties must have a 500mm minimum floor level above the “flood level for the property” - when it comes to building a new house or major extension.
A flooded street in Napier during the November 2020 floods. Photo / Paul Taylor
“Our council is very focused on preparing for any future extreme weather events, especially so since the impacts of the 2020 floods and Cyclone Gabrielle,” Napier Mayor Kirsten Wise said, upon releasing the maps publicly.
“This includes giving community tools to understand hazards.”
The flood maps are based on National Institute of Water and Atmospheric Research Limited (Niwa) data, and they could be updated again in future as new data becomes available.
Victoria University architecture lecturer Guy Marriage, who formerly worked in Hawke’s Bay, said the flood maps did not relate to river flooding like in Cyclone Gabrielle but “the amount of water that’s coming down as rain and then flooding those areas because it is all so flat”.
He said these kind of maps were necessary to mitigate flooding risks.
Part of the updated rainfall flood map for Napier. The light blue area denotes flooding up to 300mm, blue up to 500mm, and dark blue over 500mm. Photo / NCC
He said the updated maps may result in a return to more traditional forms of building homes on piles, as opposed to concrete slabs, which have become more commonplace.
“I would think that that would be the biggest logical conclusion. That people will bring in huge amounts of shingle and build up their land or else they will just say ‘look we will just build our home up on piles and we will build a raised floor which is 1m or more above the ground level’.”
He said one potential concern for architects could be maximum heights.
He said the height restriction for Napier was generally 8m for a home, which could be tight for some two-storey builds.
“Where your floor is going up by a metre, then that means the top of the roof is also going up by a metre.”
He said if “the peak of your house goes through the height limit”, people would have to negotiate that with the council.
The council will note flood risks on Land Information Memorandums (LIMs) for affected properties, which may have an impact on sale prices.
A Napier City Council spokeswoman said that in a case where a property is not in a flood zone but directly next to a road in a flood zone, any building applications would be a “site-by-site” basis. However, a new dwelling would likely need to be built at a minimum 500mm above the corresponding flood level on the road.
“In a general case where an application was proposing a new dwelling where the adjacent road is indicated to be flooded, a freeboard above the flood level in the road will be applied to enable resilience against the potential effects of flooding on the proposal.”
You can view the updated flood maps on the Napier City Council website and the Hawke’s Bay Hazard Portal.
Gary Hamilton-Irvine is a Hawke’s Bay-based reporter who covers a range of news topics including business, councils, breaking news and cyclone recovery. He formerly worked at News Corp Australia.
