Christchurch residents have protested over a council planning change they say will increase flood risk in a large part of the city’s lowest-lying coastal suburbs.

The South Brighton Residents’ Association (SBRA) says the change will remove a section from the district plan relating to an area governed by high flood hazard management rules. The area has subsided by up to one metre because of the Christchurch earthquake.

SBRA secretary Hugo Kristinsson has accused the council of providing inaccurate maps to insurer FM Global, which shows a break in the flood risk in South Brighton.

The council has also allowed houses to be rebuilt based on future assumptions about flood protection measures, he says.

Christchurch City Council has strongly refuted the accusations, with a spokesman telling insuranceNEWS.com.au it has explained to the SBRA several times that the flood maps used for planning purposes are not inaccurate.

FM Global’s flood map identifies moderate to high flood hazard in areas where flood data is insufficient. It uses hydrology and hydraulic science, and accounts for ground elevation and surface texture.

The proposed changes extend the application of a rule allowing for the replacement of houses at recommended minimum floor levels. No sections are being removed from the district plan, and minimum floor levels are required in all instances, the spokesman says.

The rule change would allow residents to repair and replace houses with properties of a similar size without needing a resource consent from the council.

However, the SBRA says Brighton peninsula needs engineered protection against flooding and erosion and, failing that, the council should implement a policy of adaptive management or managed retreat.

Mr Kristinsson says if there is no protection, insurance and mortgages will become unaffordable.

People are already living in tiny houses, buses and containers, and the standard of housing in coastal areas will continue to degrade if Christchurch City Council retreats from the suburbs, he says.

FM Global was contacted for comment but did not respond before deadline.