A retired water engineer has challenged long-accepted research that attributes some of the Illawarra's most serious landslide and flooding events to blocked drains.
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Robert French says the research is based on assumptions, and has led to onerous requirements for costly, over-engineered drainage systems that Wollongong cannot afford.
Further, the modelling allows insurers to consider lesser drains a hazard, he said.
Mr French penned an opinion piece on the issue for the Mercury in the wake of the 25th anniversary of the deadly Coledale mudslide in April 1988, as a working party prepares the latest revision of the engineering bible, Australian Rainfall and Runoff.
Mr French, from Sydney, believed the new edition of the book would be heavily influenced by Wollongong City Council policy which, since 2001, has required builders of culverts less than six metres wide to factor in the consequences of them becoming totally blocked.
For bigger culverts, a blockage of 25 per cent is factored in.
"What that does is it forces you to put in very big culverts, so you don't have to make so many allowances for water charging across the land," said Mr French, who was subcontracted to work for insurance companies in the wake of widespread flooding in the Illawarra's northern suburbs in 1998.
"This means all your culverts need to be big enough to drive a tank through, and that's costly.
"That comes out of your rates and taxes, which is fine if it stops you and your personal belongings being swept into the South Pacific Ocean.
"But if it's a total waste of time because Wollongong drains don't get blocked, then what we've done is take [ratepayers'] money ... and you get no benefits at all. It subsidises the engineering lifestyle, if you want to be really cynical."
In April 2000 a team with representatives from the Department of Land and Water Conservation, Wollongong City Council and consultants undertaking flood studies in the area, began assembling data on blockages observed after the 1998 flooding event.
They concluded there had been widespread blockages in the Hewitts, Towradgi and Allans Creek catchments, with most serious blockages in structures with an opening size less than six metres.
This was used as reason for revising the approach to Wollongong's flood planning.
Mr French believed the observations were problematic because they were made after the event.
"There's no evidence to prove that it occurred, and you can't prove it didn't occur," Mr French said.
He has also researched the April 30, 1988, mudslide that killed baby James Hagan and his mother Jennifer Hagan in their Coledale home.
He questions why an unpublished State Rail Authority report cited a blocked culvert as a contributing cause.
Drainage would not stop a landslide, he said, so the blockage was unrelated.
Mr French is calling on people with evidence of culvert blockage relating to the 1998 and 1988 events to make contact via robert.french@optusnet.com.au.
