Catherine Armitage March 26, 2012
Worried ... Bob Porter, Bart Bassett, John Miller and former councillor Trevor Devine. Photo: Dean Sewell
EXPERTS have warned that a flood in the Hawkesbury-Nepean valley comparable to the one that devastated parts of Brisbane in January last year is inevitable, with catastrophic consequences for some of Sydney's fastest-growing residential areas.
Passions are running high on the Hawkesbury following the overflow of Warragamba Dam due to flooding earlier this month.
According to residents, current planning is too focused on evacuations rather than what can be done to mitigate severe flooding. Flood-risk experts said planning authorities were not sufficiently upfront about the risks posed to residents, most of whom would be unaware that their houses were built on flood-prone land.
State government emergency planning for the Hawkesbury-Nepean basin is based on the likelihood of a repeat of an 1867 flood, which inundated 200 square kilometres of north-western Sydney including Windsor, Richmond, Pitt Town and Riverstone and the present-day suburbs of Bligh Park and McGraths Hill.
''At some time in the future a flood of this  magnitude will occur. It is not a question of if, it is a question of when,'' the state planning co-ordinator of the NSW State Emergency Service, Steve Opper, said.
The member for Londonderry, Bart Bassett, wants further investigation of the use of Warragamba Dam for flood mitigation as well as water storage. Mr Bassett said the service would be ''stretched'' by the scale of evacuation required in the event of major flooding on the Hawkesbury.
Historian and flood mitigation activist John Miller, 83, has seen the river flood numerous times and confesses he is ''terrified'' at the prospect of a big flood. ''We may get enormous loss of life,'' he said.
Current planning is based on a one-in-100-years event - that is, a flood with a 1 per cent chance of happening in any given year, the peak for which was previously thought to be 16 metres at Windsor Bridge but has been revised to 17.3 metres.
The government says that it will establish a review into flood planning.
Former councillor Ted Books remembers rescuing people with an army duck in the 1961 flood, which went to 15.07 metres. He has been dismayed successive rises in the flood planning control level have put his home in a flood risk zone. ''It has dropped my [house] value by $150,000,'' he said.
Hawkesbury City Council's draft flood plain risk management plan will be revealed later this year. However, Hawkesbury councillor Bob Porter has been removed from the council's flood plain management advisory committee for publicly criticising a recommendation that any new houses in flood-prone areas should be two storeys.
A flood plain management strategy document produced by the state government 15 years ago for the Hawkesbury-Nepean estimated 7000 houses would be inundated, 2000 houses destroyed and 40,000 people would need to be evacuated if a flood comparable to that of 1867 were to recur. Likely damage was estimated at up to $2.5 billion.
New residential developments on the flood plain have increased the likely magnitude of impact.
Home owners or buyers are not routinely provided with information about the specific risks to their properties.