Extreme weather events are driving the one in 100 year flood levels to new heights with increases of metres rather than centimetres.

In June 2023 the NSW government gazetted its Flood Risk Management Manual after new measurements were used to provide probable maximum flood levels.

Maximum levels referred to a one in 100 year flood that was based on data from the 1971 floods. Following widespread flooding over the last couple of years and in particular in Lismore and the Hawksbury/Nepean catchment, the NSW government commissioned an independent inquiry.

Flood levels in 2022 exceeded previous maximums and now the reference point for flood mapping has been changed.

Councils are responsible for providing their own flood maps and making them publicly available, the Department of Planning and Environment said. They are used by insurance companies to gauge levels of risk.

Flood mapping is only just becoming available for some regional councils who have battled, and continue to experience, extreme shortages of planning staff.

In the Bega Valley mayor Russell Fitzpatrick said there were increases of 3-4metres in the maximum flood level in some areas and it had already affected one development with other areas in the shire, of concern.

"A residential block (in a one in 100 year flood zone) will need vehicular road access to higher land," Cr Fitzpatrick said.

He plans to ask a question without notice at the next council meeting (January 31) to get information into the public domain.

In January 2023, the NSW Department of Planning outlined proposed changes to strengthen planning rules to better protect and manage new development in areas that could be at risk during floods, through a special flood considerations clause (5.22) to be inserted into Local Environmental Plans.

The clause covers sensitive and hazardous development, such as caravan parks, hospitals and seniors housing, between the flood planning area and the probable maximum flood level.

It also covers development that is not sensitive or hazardous but on land council considers may pose a particular risk to life and where people may need to evacuate or there are other safety concerns, in the event of a flood.

For any development falling under the terms of the flood clause, council must consider how easily it is to evacuate, the measures to manage risk to life and whether the development could adversely affect the environment in the event of a flood.

The NSW government said clause 5.22 was intended to strengthen planning rules to protect and manage development in areas that could be at risk during flooding by applying additional planning controls.

"This will help reduce the extent of property damage and potential loss of life and build greater resilience into NSW communities."

A number of councils have ensured new flood height planning controls cannot be applied retrospectively to a DA submitted before November 10, 2023 when the amendment became law.

"A development application made, but not finally determined, before the commencement of State Environmental Planning Policy Amendment (Flood Planning) 2023 must be determined as if that policy had not commenced" is the clause inserted into their Local Environmental Plans.