Tamar River estuary raking called off by City of Launceston council

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Posted October 15, 2019

Raking the sediment in the Tamar River estuary has been found to be less effective than first hoped.

The City of Launceston Council has called off any further raking in light of the Sedimentation Management Report release and is considering returning to the more expensive, but effective, action of dredging.

The council will discuss the report at its meeting next week.

However, environmental scientist Rebecca Kelly, who has been studying the river for 12 years, said the estuary was not abnormal.

"The mud flats are not made of sewage. They're not there because of the sewage," she said.

"The mud flats are there because of the natural infilling process that the estuary is going through because that's what these types of estuaries do."

The council's environmental scientist Kathryn Pugh supported the comments.

"We have photos from the 50s showing mud flats and people calling it a disgrace," she said.

In the past few years, there has been an increased number of boats getting stuck in the river's infill, which is what is hoped to be fixed by dredging.

The report considered other research which found increased flows did not help address the issue. The 2016 floods did move some of the sediment just down the river, but it returned within months.

"The sediment review didn't look at water releases," Dr Kelly said.

"There was a separate view released by Tamar Estuary Management Taskforce. They looked at flow release scenarios and what it found was that it's really a negligible amount of sediment that can be removed ... and that it comes at a cost of $100,000 or more."

Ms Pugh said the council would come up with a short-term plan to manage the sediment.

"We understand that we have lost navigation channels in the estuary, so we need to implement a plan to restore those channels," she said.

"That will probably involve a short-term dredging program just to get those navigational channels back and then there will be a longer-term plan on how we manage the inter-tidal mud flats and the navigational channel."

The dredging program will start as soon as possible, with Ms Pugh saying a team was already working on it. It is unknown how long the dredging program will take as it depends on the volume that needs to be removed to restore the channel to the required depth.

The removed sediment would be taken to the dredging ponds located further down the river.

She said it was important to understand the mud flats were a natural part of the system, and would not be dredged.

Some restoration projects will also be carried out on the foreshore to make the river look more attractive.

The council infrastructure services director Shane Eberhardt said dredging was the obvious solution as it removes the sediment from the estuary, but the council was still in the process of looking at the options.

"It has to be stored somewhere and then disposed of ... it's a far greater cost going forward," he said.

The Launceston Flood Authority, funded by the council and the state government, would be responsible for the dredging.

"The state government are part of the Tamar Estuary Taskforce, and part of the investigations, so they're well aware of the outcomes of the study," Mr Eberhardt said.

Sediment raking was first trialled in 2012 and has been occurring since.

The council meeting will be held at 1pm on Thursday, October 17, at the Town Hall.

Source: examiner.com.au