WORK is set to start next week on the construction of a new pipeline and outfall to discharge treated water from New Norfolk’s Turriff Lodge treatment plant into the River Derwent, bypassing the man-made wetlands area that was constructed in the 1990s.
This work will involve the closure of the wetlands walking track from early next week until late June. A TasWater spokesperson said this work had already been approved by the Derwent Valley Council and was separate to the proposal to decommission the wetlands – which is presently before the council for consideration.
“We are re-establishing the old Turriff Lodge Sewerage Treatment Plant outfall back into service and making it compliant with modern standards,” TasWater general manager (project delivery) Tony Willmott said. “This will be a far superior method of discharging the treated effluent to the poorly performing wetland. New Norfolk is a beautiful and rapidly growing town, and one of TasWater’s priorities is to improve the area’s public health and environmental outcomes.”
“The new outfall will extend 14 metres into the river to a depth of six metres, and a new diffuser will aid dilution and dispersal. This will improve the local water quality and provide better protections for public health and the local aquatic ecosystem,” Mr Willmott said. Construction of the outfall will involve the use of a boat, divers and a barge for pile driving into the riverbed to anchor the new infrastructure into place.
TasWater hopes that by the time the new outfall is diverting effluent away from the wetland, council approval will have been received for work to start on filling the area. “We expect this work to begin in April. Transforming the wetland will involve removing the reeds and managing the many weeds on the site, as appropriate to each species, then allowing the area to gradually dry and drain, which may create a short-term increase in odour.
“Rock, fill and topsoil will be brought in, before seeding the area with grass. Filling the wetland will be a significant task, with approximately 14,000 cubic metres of fill to be transported to the site from the nearby Bryn Estyn Water Treatment Plant. A very small number of trees will need to be removed or pruned for this work to occur, but the vast majority of established trees will be kept in place, so they can continue to provide habitat for birds, be enjoyed by visitors and screen the sewage treatment plant from sight.
“Our environmental assessments have determined this work can be undertaken without risk to threatened species. We’re investing in an environmental management plan that will guide our activity to ensure we can limit our impacts on the local environment. For example, we are taking steps to ensure any platypus in the area maintain uninterrupted access to the river.
“We understand the importance of this foreshore area for locals and visitors to the Derwent Valley, so all work is being carried out within conditions set by the Environment Protection Authority, the Tasmania Parks and Wildlife Service, and the Derwent Valley Council.”
The wetland was built in the 1990s as a series of lagoons to provide additional treatment for effluent from the adjacent sewage treatment plant, which at that time was owned by the council. “The wetland no longer provides any treatment benefit and will only worsen over time, so the area will instead be bypassed using a new underwater outfall. This will remove the effluent from the wetland and enable the area to be remediated,” Mr Willmott said.
“This project has been discussed for many years, and a process of public consultation by the Derwent Valley Council in late 2020 found community support for the project. The wetland walking track will be temporarily closed to the public for the duration of the works, from early March until late June 2023.”
Picture: The Turriff Lodge sewage treatment plant, wetlands area and River Derwent at New Norfolk.