Raking the Tamar is not the silver bullet solution it seems

Last week community group the Tamar Action Group called on the Tamar Estuary Management Taskforce to reinstate raking as a matter of urgency.

TAG spokesperson Andrew Lovitt said at the time restoring raking would reinstate the community's faith in TEMT, and vented frustration about the slow pace of change in the estuary's appearance.

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The issue of sediment build-up on the estuary is frustrating river users, with dire consequences on the horizon if no action is taken.

A number of community groups have cited sediment build up as their main concern about the river and say its aesthetics and uses are limited because of the mud.

The City of Launceston council was raking the estuary between 2012 and 2018, in funding collaboration with the state government.

Raking is the process by which a barge travels along the estuary and stirs up parts of the sediment build-up into the water, which is then pushed to other parts of the estuary.

It differs to dredging, whereby sediment is pumped out of the water and dumped on land or used for other purposes. The Tamar Estuary has been both raked and dredged in the past.

The City of Launceston, on behalf of the Launceston Flood Authority, gained a permit from the Department of Primary Industries, Parks, Water and Environment to rake the Tamar.

In 2019, the council announced it had halted the process, as a condition of the permit required an independent report of its impacts be conducted.

That report was conducted by TEER scientific and technical committee chairwoman Rebecca Kelly.

Dr Kelly said what she examined was did the raking work and what was the impact on water quality. She said when considering whether raking was effective she looked at three prongs: was there less sediment, was the visible mud flats removed and how did the raking effect water quality.

She said the Launceston Flood Authority's permit required it to conduct water quality testing on the day of raking, to look at the impact the work was having on water quality in front and behind the barge, but no non-localised work was required.

"What we found when we looked at the question of whether it was effective, was no, it wasn't," she said.

The sedimentation on the mud flats was not dramatically reduced. by the raking operations. Sediment is pushed tidally, so it may have been moved around elsewhere but it would eventually settle back in place.It also caused sedimentation to be pushed into the channels, where it affected users such as the Home Point cruise ships.

Dr Kelly said there was no data collected that would categorically show the impact the raking had on the estuary's fish and bird life, but there were some indications that it had significant consequences.

"The silt binds up the heavy metals, so what happens is when the pollutants enter the water the mudflats sort of bury them," she said.

"So when raking was occurring it was pulling up the sediment and releasing those metals and other pollutants into the water."

Water quality was downgraded during that time, but the most recent report from TEER showed the water quality had improved, which Dr Kelly said was a result of not raking the estuary.

Dr Kelly said the visible mud flats had come back, which is why she understood the community concern.

However, she said data collected on sediment levels in the estuary showed that there was not significantly more mud than in the past.

She said sedimentation build up was a natural part of how the estuary functioned, and it did unfortunately build up in places where there was a lot of infrastructure - such as the marina.

The Tamar Yacht Club is on the brink of moving its headquarters from Launceston to Beauty Point, which echoes moves by Launceston developer Errol Stewart.

Mr Stewart, who was the driving force behind the development of Launceston's Seaport, said he has plans to move his marina from the Tamar to Beauty Point.

Both cited concerns over mud and sediment build up, making mooring boats impossible. Tamar Rowing Club have also cited concerns over the mud build-up, saying they have not been able to row on the estuary because of it. Sediment management solutions have not yet been revealed by TEMT, but it's understood potential alternative solutions are being examined.

TEMT is examining alternative proposals for sediment management of the Tamar Estuary in a report that's due for release this year.

The report, which will examine future management of the estuary is expected to be released this year.

TEMT chairman Gary Swain said new work in sediment management was underway, which he said would help guide future decision making.

"At the most basic level there are two challenges facing the estuary - water quality and sediment management," Mr Swain said.

"The River Health Action Plan is primarily focused on the former, and is already making significant gains in terms of water quality improvements in local waterways."

Mr Swain said while sediment was not a challenge for the health of the estuary, some people find it an aesthetic challenge.

"TEMT is undertaking a scientifically robust, evidence-based evaluation of the wide range of sedimentation management options that have been proposed for the estuary," he said.

TEMT expects to complete this work in the first quarter of 2021.