An investigation into Launceston’s historic combined drainage system is underway which includes the development of a strategy by TasWater for its future operation.

This project is made possible by $3 million in funding secured by Bass MHR Andrew Nikolic during the 2013 Federal Election, for the Tamar River Recovery Plan. The Tamar River Recovery Plan is a collaborative project involving Launceston City Council, NRM North, Launceston Flood Authority, TasWater and the Australian Government’s National Landcare Programme.

The first pipes in Launceston’s combined system were installed in the 1860’s, the oldest parts of the network still in operation are now more than 130 years old.

It is the last combined drainage system of any significant size still operating in Australia and collects flows from the central city area, South, West and East Launceston, Newstead and Invermay, covering about a third of Launceston’s 30,000 properties.

TasWater’s Manager Asset Strategy, Andrew Truscott says a combined drainage system transports stormwater and sewage to a treatment plant in the same set of pipes.

“During periods of high rainfall the combined drainage system is designed to overflow to prevent local flooding. These overflow events are referred to as combined sewer overflows, during which diluted, untreated sewage is discharged to the North Esk and Tamar rivers.”

“When this happens, the impact can be partially mitigated by screening which removes sewer rubbish such as gross solids (e.g. sanitary products, bottles, cans), grit and gravel and the litter in street gutters which wash into the drainage system during wet weather.”

TasWater has recently recommissioned a gritter machine at the St John Street Sewer Pump Station to improve the screening and solids removal process.

“The gritter is located more than eight metres underground and uses a series of buckets to capture sewer rubbish before it gets into the river” Mr Truscott says.

This project has been undertaken as part of $500,000 provided under the Australian Government’s Tamar River Recovery Plan.

Member for Bass, Andrew Nikolic MP says ‘‘the upgrade of the gritter, via Australian Government funding, is providing immediate benefit and is already reducing the amount of pollution entering the Tamar River.”

For the longer term, funding is also being provided for TasWater to investigate options to better manage the stormwater and sewage collected by the combined drainage system.
TasWater’s Andrew Truscott says “the key outcome of the investigation will be a strategy to identify ways to improve the operation of the combined drainage system. A capital and operational works programme will also be identified to help reduce the impact of overflow events on the city’s waterways.”

The strategy development has been awarded to Beca, a consulting firm with extensive experience working with combined drainage systems in the United Kingdom and New Zealand. Beca is using a UK derived and accepted methodology for developing an effects based combined sewer overflows (CSO) mitigation assessment.

Ian Garside, Beca’s Technical Director says it is an approach based on the Urban Pollution Management (UPM) methodology and has been selected as it will allow key stakeholders to be taken on a journey to understand the effect of CSO discharges on the health of the receiving environment.

“This effects based approach will allow the team to develop a targeted programme which can prioritise work to mitigate health risks to both the public and the river from CSOs and the combined drainage network.”

Beca will be able to use its background to help TasWater identify areas for improvement and to align with industry standard practices for other authorities.

An education programme will also be developed to build a better understanding among the Launceston community on how the combined drainage system works.

The initial investigation and strategy works is scheduled for completion late this year.
Simon Pilkington, TasWater