As the Mercury’s flooding investigation continues, BEN LANGFORD finds a government agency willing to do mitigation work – but it has been told to wait.
Another major piece of flood mitigation work recommended in the wake of the 1998 floods is on hold pending the completion of a review by Wollongong City Council.
But despite residents' frustration with flood studies, plans and reviews, this indecision might not be a bad thing, according to a leading engineer.
Roads and Maritime Services (RMS) has offered to remove the disused truck safety ramp at the base of Bulli Pass, but the council rebuffed the offer.
''It would be an extremely effective debris trap ... it doesn’t make sense to remove the safety ramp if you’re not going to do anything to the culvert.''
The ramp's modification was recommended as a high priority in the Hewitts Creek flood study and management plan in 2002, as was the enlarging of the 2.4-metre culvert under the railway line that takes Woodlands Creek towards Sandon Point.
That study is now being reviewed, with technological improvements and surveying errors, plus new infrastructure, being taken into account.
Residents of Hewitts Ave have complained of skyrocketing insurance bills and difficulty getting approval for renovations, since they were classified as being at high risk of flooding - despite the homes never having flooded.
Their pleas for mitigation works - the culvert, the ramp and clearing vegetation from the overgrown creek - have gone unanswered.
In an email to a resident, an RMS planner confirmed its offer was on hold.
"Retaining these structures awaiting the outcome of the study has been specifically requested by Wollongong City Council," he said.
"The Roads and Maritime Services remains committed to undertake whatever works are required to decommission this redundant part of the Princes Highway."
Residents are likely to face further frustration and delays, as new modelling will need to be done to see the effect of removing the ramp.
But at least one experienced engineer said unless the culvert were to get a multimillion-dollar upgrade, the ramp should stay in place - with other, cheaper, mitigation works performed instead.
Paul Nichols, who has 35 years' experience in urban infrastructure development and flood modelling, said there was a simpler and less expensive solution - transform the old ramp into a debris trap to hold back water and limit blockage.
A side spillway could allow water, but not debris, to flow to the culvert.
"It would be an extremely effective debris trap, to the point that you could [have] a much lower debris factor," Mr Nichols said.
"It doesn't make sense to remove the safety ramp if you're not going to do anything to the culvert."
He said this debris trap could stop the culvert under the railway line becoming blocked - perhaps reducing the need for a larger culvert, meaning this could be a significantly cheaper and quicker solution.
"You can be assured that 2.4-metre pipe won't block and it can take most of the flow [if the debris trap was built]."
Mr Nichols said this could reduce the modelled effect of flooding on some properties by more than 40 centimetres, and up to 1.6 metres.
WCC manager of infrastructure strategy and planning Mike Dowd said the council was still "investigating options for the land", which RMS had offered to hand over.
"As part of the Floodplain Risk Management Study, flood modelling will be undertaken to determine the changes in flood levels and behaviour if the safety ramp is removed.
"Following completion of any works, council will be able to quickly change flood mapping to reflect the resulting improvements."
The present review of the Hewitts Creek study, being undertaken by consultant engineers BMT WBM Pty Ltd, was commissioned in August 2012 at a cost of more than $100,000. A draft report is on track to go to the council in February. If the council accepts it, a process of developing a new Hewitts Creek Floodplan Management Study, then Plan, will commence.
Mr Dowd could not say whether the ramp was an asset or a detriment for flooding purposes before it was fully assessed.
"The draft Hewitts Creek Flood Study analyses existing flood behaviour based on existing landform only and does not consider what effect changing the safety ramp has on flood behaviour," he said.
"The impact of changing the safety ramp on flood behaviour will be assessed as part of the Floodplain Management Study.
"It's important for council to carefully assess any proposed changes to the floodplain such as the removal of the safety ramp to ensure that it does not make flooding worse."
A spokesman for RMS this week said it would wait until the study was complete and the arrester bed would be removed if it was a recommendation of the council's updated risk management study.
Stormwater channel so clogged it resembles dam wall
Clarrie Bouma has lived in Hewitts Avenue for two decades – long enough to remember a channel almost two metres wide between the back of his property and the railway line.
He could stand in water up to his waist, and it served as the main way flood waters could flow from Woodlands Creek to the larger Hewitts Creek and out to the sea.
Now, the channel is mostly filled in, with Mr Bouma’s back vista like looking at a dam wall. He fears that if a large flood occurred, the water would have nowhere to go.
Mr Bouma, a surf photographer and musician, said over several years, railway work crews had dumped dirt, concrete, sleepers and other fill in the channel, filling it up and making maintenance impossible.
‘‘We have the double whammy where we have the decreased water carrying capacity of the drain, and we can’t clear it, because tractors can’t get access,’’ he said.
‘‘The slasher used to come in here and slash all the hillside.
‘‘They used to come in with a digger and clear the drains out.
‘‘Now we get water in our backyard from a non-major rain event. It’s so frustrating.’’
The channel is now about 30centimetres wide and mostly useless as a path for water to escape.
Mr Bouma, 64, said a representative from the Transport Department was there this week examining the fill.
The Mercury put Mr Bouma’s concerns to Sydney Trains.
A spokesman said it would inspect the site and improve its appearance.
‘‘A dirt mound was put in place in the railway corridor in July 2010 to reduce noise for neighbouring residents,’’ he said.
‘‘Sydney Trains is aware of only one complaint by a resident that the mound causes drainage problems.
‘‘Engineers will inspect the site and advise whether the mound has any impact on flooding risk for Hewitts Avenue residents. Sydney Trains will be trimming back the vegetation and removing discarded sleepers and rail track to improve the site’s appearance.’’
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