ACF branch calls for flood model for a changing climate

Central Coast Council should reveal its flood modelling assumptions and discuss them with the public, following recent flooding on the Woy Woy Peninsula, according to the Central Coast branch of the Australian Conservation Foundation.

Branch president Mr John Wiggin said it was important that these assumptions were discussed, before decisions were made about solutions proposed to alleviate the situation.

"The history of council planning on the Peninsula is one of looking in the rear view mirror," said Mr Wigggin.

"Planning for life in a changing climate relies on the accuracy of our projections and the modelling of changed conditions.

"We have looked back at the past and expected the same for the future.

"Our projections have been based on more of the same, refined only by the accumulation of data as the years roll by, to be inserted in the same linear models."

Mr Wiggin said that the name "The Everglades" was instructive.

The Peninsula had been a wetlands since before white settlement and, with climate change, was likely to be so.

He said that environmentalists had called for the restoration of Teatree Creek, which council engineers refer to as the Everglades main drain, at the time Kahibah Creek was restored several years ago.

The methods used were effective in providing drainage while maintaining the endangered bushland, through which it passed.

Teatree Creek needed similar treatment.

He said Teatree Creek was bordered by Umina Coastal Sandplain Woodland along its length, including in the secondary college grounds, on private land near the corner of Hillview St and Veron Rd, and at the Burrawang Reserve which fronts Railway and Hillview Sts.

Mr Wiggin said the council had given much lip-service to "water-sensitive urban design", but there was little evidence on the Peninsula that these words meant anything in practice or that the "infiltration devices" used by the council had any demonstrable effect.

He said that the council was ignoring the reality of climate change and was continuing to excuse its policies and performance on the basis of "exceptional" occurrences - usually labelled as "recent storm events".

"The concept of 1-in-100 year flooding ('1% AEP') only makes sense in rear-view-mirror linear modelling," Mr Wiggin said.

"With climate change already showing its impact, we are having 1% AEP events at the frequency of 20% AEP events.

"When flooding rarely happens, it is easy to dismiss a local flood, such as at Lovell St, as just a "local blackspot drainage problem".

"When they become more common, it is clear that Lovell St is not an isolated example.

"They are now happening in residential streets all over the Peninsula and are disrupting traffic on major thoroughfares such as Hillview St and Veron Rd, which will be even more heavily trafficked when the Bull's Hill rail underpass eventually comes on line.

Mr Wiggin said that the models needed to change.

"Static models that predict a 20mm flood level rise at Lovell St in a climate that results in a 900mm sea level rise do not make sense.

"By the council's own admission (in a letter from mayor McKinna to local residents), these floods are the result of circumstances not seen before or at least very infrequently.

"We are entering a new era and a new approach is needed, with the acknowledgement that areas that were not previously flood liable will soon fall within the historic definition."

Mr Wiggin said that the council needed to look again at the way it interpreted its data.

"Any action needs to be predicated on an admission of the predicament that we are in.

"A denial of this will only lead to solutions that will not address the problem, and will ultimately be a waste of our money and will cause more distress to our community than necessary.

He said the council should review its town planning approach: "Planning requirements cannot sustain a backward-looking approach."

He said that secondary dwellings were a case in point.

"With onsite detention systems designed around historic flood frequencies, it will only exacerbate the problem.

"In any case, they create more runoff due to the associated paved ground for driveways and pedestrian access, irrespective of limits to floor area, and no measures are put in place to deal with this."

Mr Wiggin said that the council seemed to forget that drainage "assets" on the Peninsula actually belonged to the ratepayers.

"They do not belong to the council. The council, at best, holds them in trust for us.

"It is hard to believe that there is any genuine concern for the Peninsula when the council has a track record of milking the unsophisticated Peninsula community of millions of dollars earmarked for drainage ... and diverts it to influential and luxurious areas such as Terrigal.

"While the drainage backlog in the Gosford remains at $175 million in annual budget of $300 million, it is clear that the council has no serious intention of addressing this issue effectively."

Media release, 28 May 2016

John Wiggin, ACF Central Coast