Flood protection work for Phoenix Dam
Clutha District Council (CDC) is working with the owner of the 160-year-old Phoenix Dam the Otago Regional Council as the regulator, and Emergency Management Otago to ensure the dam's continued safety.
CDC’s Service Delivery Manager Jules Witt said Lawrence’s water supply comes from Bluejacket Gully creek, which was fed from the dam, with a resource consent being held by CDC for the damming of water. The dam is on land owned by Port Blakely Limited.
Dam safety inspections by Opus (2006) and Riley Consultants Limited (2021) identified several potential dam safety deficiencies, condition issues, and areas of uncertainty with respect to the dam. These inspections were for CDC as the consent holder.
Riley was initially commissioned by CDC and then later by Port Blakely Limited to carry out preliminary geotechnical investigations, perform preliminary stability and spillway capacity analyses to determine whether the dam meets the criteria for being ‘dangerous’, ‘flood-prone’ or ‘earthquake-prone’ under Building Act.
Mr Witt said parties have decided to begin a controlled emptying / dewatering operational plan to initially lower the level of the dam by 3 metres, by way of a siphon system.
Phoenix Dam is a historic water supply dam located 3km north-east of and above Lawrence, Otago. The dam was originally constructed in c.1863 for goldmine sluicing.
“This work started today and involves water being drained by siphon from the dam to the creek below the dam, an existing waterway. The main equipment for the operation was transported to the dam by helicopter and is being installed, along with flow meters to monitor the water flow.”
Mr Witt said the operation is being undertaken to significantly reduce the impact of risk of any potential failure of the dam. The dam has been assessed as higher risk under the building act.
“The dam site is not earthquake prone, however there is a flooding risk at the area. There is no evidence of overtopping of the dam recorded since 1864.”
It is expected to take several months to reduce the level.
The operation has been assessed and is not expected to have an impact on water supply, but Council is closely monitoring and managing this.
The operation site has been marked off by hazard tape and due to health and safety hazards, including heavy machinery, it is advised that the public avoid the area.