In 2008, Sue Ribbons, then a senior engineer at Sydney flood specialist company Bewsher Consulting, wrote a paper entitled The Risk of Flooding – What are the People of the
Hawkesbury-Nepean Willing to Accept?
People had become “comfortable” with the idea of the 1: 100-year flood which had led to a
false sense of security that bigger floods were not possible, she wrote. “If the` rules ‘for developing on flood-prone land were changed today, the community `outrage’ would probably be extreme. Yet would this outrage be worse, if things are allowed to continue as they are, and another `1867 flood ‘struck the valley?”
For 15 years as a local newspaper journalist, I listened to long, often heated discussions about flood mitigation and impassioned warnings from old-timers about the 1: 100, 1: 500 and the legendary 1: 1000-year “PMF” or probable maximum flood (we haven’t quite reached that level yet, despite Premier Dominic Perrottet referencing it this week). For the record, the old-timers’ warnings were largely not taken seriously.
Last March, former SES deputy commissioner Chas Keys, an opponent of state government plans to raise the height of Warragamba Dam wall, urged it to invest instead in flood-mitigation infrastructure to prepare for a deluge bigger than the 1867 benchmark. “ There is nothing to say that that is the worst flood that could happen – you could get well over 20 meters, “Keys told The Sydney Morning Herald. “It would be very rare, it could be once in a few hundred years or even a thousand, but the trouble is it is inevitable.”
If routes out of the flood-prone areas were not built, he said, extreme floods could cause hundreds of deaths as people cut off retreated to islands before being washed away. Keys also warned the government should halt plans to build more housing on the floodplain below the dam to double the population of the Hawkesbury-Nepean valley to 250,000 people over the next 30 years.
“I know it’s a growing metropolitan area and they’ve got to go somewhere,” he said. “But I do not think they have to go into an area that’s got this serious and well-known problem.”
Renae Hanvin has created the Business Community Resilience Toolkit pilot program to help businesses prepare for disaster. She has been banging the disaster resilience drum for a decade. Nobody listened until the disasters began piling up. Now everyone’s an expert.
“We’re living in an era of compound disasters, which means it’s not` if ‘but `when’ you will experience a major event like flood or bushfire,” Hanvin says. “The time to prepare is now.”
Meanwhile, trees on the banks of the Hawkesbury-Nepean River are again entangled in
weeds. What is left of them.
The modern bridge over the shallow crossing is again submerged. It’s time to prepare the ark.
Ellen Hill is a freelance journalist and communications consultant. She has previously done consulting work for Renae Hanvin.