Any national flood-mapping scheme could be “overly conservative” in its assessment of which areas are at high flood risk, potentially penalising affected homeowners with higher insurance premiums, a leading hydrologist has warned.

Mark Babister, MD of hydrology firm WMAwater and Chairman of the National Committee on Water Engineering, says many local councils – one of the main producers of flood maps – take a conservative approach when plotting flood maps because of concerns over liability.

Mike Rothery, First Assistant Secretary of the National Security Resilience Policy Division in the Attorney-General’s department, agrees, saying there are “difficulties” with local governments that are afraid of publicising data which could give rise to compensation claims over land use.

The comments were made at the Institute of Actuaries flood resilience seminar last week.

Mr Rothery says the Federal Government is currently undertaking an analysis of flood mapping, comparing what exists to what is required.

But he says that because different users – such as councils, land planning agencies, insurers, homeowners and the state emergency services – have different needs, defining the right approach is difficult.

Mr Babister says he recently told the Government that completing a national flood map would cost around $300 million, using light detection and ranging aerial mapping technology that would produce maps accurate enough to be used in land planning.

He says that despite the different specifications required by different map users, any national mapping scheme would need to be “one size fits all” to enable the public to understand it.

The maps would need to be designed to the highest specification required, which is that of land planning authorities and councils, which typically require them to be accurate to within +/- 300mm.

He says that due to political sensitivities around the production of flood maps, such as the different requirements by different groups, including home-sellers in flood-prone regions who would not want maps to be publicly available, the process is less straightforward than simply a question of who should pay for national flood mapping.