Decommissioning two out-of-service water supply dams
Client: TasWater
Location: Queenstown, Tasmania
Date: August 2013 – April 2015
Decommissioning two out-of-service water supply dams to reduce risks to the community, reduce costs to the client, and restore the local environment and waterways
Background
TasWater’s Cutten Street Dam No 3 and Roaring Meg Dam originally formed part of Queenstown’s water supply system. As these dams were no longer used for water supply, and were considered to pose significant risks to the community and the client, TasWater decided to decommission them. Roaring Meg Dam overtopped in August 2013, significantly eroding the downstream face of the dam at three locations and increasing the urgency for early decommissioning.
Solution
Entura undertook a study of the Aboriginal and historical heritage of the area, as well as flora and fauna studies and fluvio geomorphological studies. The design work included preparing a dam safety emergency plan, sediment and erosion management plan, creek diversion, dam excavation sequence, stockpiling of excavated material, rehabilitation of the exposed reservoir bed, hydraulic modelling of the creek, and rock lining of the creek channel through the exposed reservoir. Entura also prepared necessary documentation to obtain permits from the State Dams Regulator to decommission these dams.
The decommissioning work was undertaken in March 2015. Entura provided owner’s engineer services to TasWater and supervised the decommissioning work. A decommissioning report was prepared at the end of the work, which was submitted to the State Dams Regulator.
Outcome
The dams were successfully decommissioned and the exposed area rehabilitated without any safety issues or impacts on the schedule or budget. This was the first time any dams had been decommissioned by TasWater or its previous water management bodies. Entura’s previous experience in preparing a dam decommissioning procedure for Tasmanian dams in collaboration with the Department of Primary Industries, Parks, Water and Environment (DPIPWE) and Entura’s profound knowledge of TasWater dams in Queenstown enabled Entura to undertake the whole process through to decommissioning and site rehabilitation, achieving a successful result within the client’s specified time and budget.
