Aerial photo of Lismore during the March 2017 Flood.
Aerial photo of Lismore during the March 2017 Flood. Westpac Life Saver Rescue Helico

Plan to 'flood proof' Lismore comes with massive price tag

AN AMBITIOUS plan to carve a 300m wide channel behind South Lismore to potentially floodproof the Lismore CBD has been costed at a whopping $90 to $120 million.

The proposed 4m deep channel to divert floodwater away from the CBD would involve the excavation of two million cubic metres of soil.

The channel would run from Kyogle Rd west of the South Lismore levee, run south past the Lismore airport, and rejoin with the Wilsons River at Loftville Bridge on the Casino Rd.

The idea of the channel is to divert the massive quantities of water that run down Leycester Creek in flood, which represents two thirds of the Wilsons River catchment.

It was of several options considered by Lismore City Council's Floodplain Management Committee in the wake of last year's disastrous flood.

Committee chairperson and councillor Bill Moorhouse said the total cost of the March 2017 disaster in the realm of $200 million, so the council had a responsibility to investigate every option to mitigate future floods.

"If you build that channel big enough you can basically divert all that water coming down the Leycester down through that channel," Cr Moorhouse said.

But at $120 million, he said it was doubtful that any government would be rushing to fund it any time soon.

"The problem is to build it big enough, and build all the infrastructure to go with it."

As a result of the prohibitive price tag, the committee opted to pursue more cost-effective strategies which have been considered as far back as 1995, following the massive 1989 flood.

Cr Moorhouse said these combined measures, costed at just $12 million, could reduce a major CBD flood by as much as 600mm.

The March 2017 flood went over the levee by 700mm.

"If you took 600mm off that it's only just going to run over the top and for a much shorter time," Cr Moorhouse said.

"It would have just gone over the top of the levee and probably filled the basin... the lower shops would have certainly flooded but a lot of the shops wouldn't have got nearly as wet."

The planned work will include:

1. The removal of viaducts from the railway line south of Kyogle Rd which will allow more floodwater to be directed away from South Lismore and down the airport floodway.

2. Excavation of the airport floodway by removing approximately 400,000 cubic metres of soil from high points in the floodway. This has been costed at $8 million.

3. Removal of the unused railway embankment along the side of Kyogle Road.

"The information presented to the committee indicates that works of this nature will produce substantial flood improvement for the city and can be achieved at a reasonable cost and in a relatively short period of time," Cr Moorhouse said.

The council will require Federal or State funding to be able to commence on the projects and is hoping to have the funding promised within the next 12 months.

Cr Moorhouse said in light of the $200 million damage bill of the last flood, "spending $12 million to make a difference is not a bad thing at all. It's fairly good value."

In the long-term, there is still more modelling to be done.

"The complexity of the flood model and potential for the city to be flooded from both Leycester Creek and the Wilsons River means it is going to take some time before all the possible flood improvement options can be examined and costed in detail," Cr Moorhouse said.

"We believe that substantial improvements can be made to reduce the impact of flood on the city however it will never be possible to completely flood-proof Lismore."

"The next step is to finish the flood modelling, and raise the South Lismore levee. And following that look at what we can do for the CBD."

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