Clutha District Council (CDC) has submitted a consent application to the Otago Regional Council (ORC) to divert the stream above Phoenix Dam and form a bypass to ensure the supply of water will continue for Lawrence.
Deputy CE Jules Witt says “There is a high degree of risk to the Lawrence water supply from an inadequate supply for the catchment, along with water source quality concerns, as the level of Phoenix Dam continues to reduce.”
While there is a boil water notice in place for the Lawrence township this relates to a separate issue due to problems with water treatment at the plant regarding chlorine levels.
Flood protection work to lower the level of the Phoenix Dam involved a controlled dewatering operation which began in November 2023, a joint operation involving the dam’s landowner Port Blakely Limited, CDC, ORC and Emergency Management Otago.
The flood protection work involved lowering the level of the dam by 3 metres by way of a siphon system and was achieved at the end of January. The dam has now been lowered to 4 metres as water continues to be pumped to provide the town’s water supply. Recent rainfall has lifted this level back to 3.5 metres.
Mr Witt said Council has been formally notified by Port Blakely Limited of its intention to decommission its dam due to ongoing safety concerns related to the age of the dam and a plan on how to continue supply to Lawrence had been worked on.
Council has submitted its consent seeking approval for the bypass and associated works. In advance of consent approval, under section 330 of the Resource Management Act 1991 Council has notified ORC that work on the bypass will be commencing immediately.
“The urgency of this work is that we predict the bottom 25% of the water within the dam will be unusable because of poor quality.
“It is also estimated that we have around 4-6 weeks capacity remaining and will be subject to incoming flows such as recent rainfall, which is why we need to get moving on the construction of the bypass,” Mr Witt said.
As a network utility operator, or lifeline utility CDC holds the ability to undertake the required works under emergency provisions. Council is required to notify the consent authority ORC within 7 days, that the activity has been undertaken. Notification was issued on 9 April 2024.
The work involves construction of a small temporary weir to aid with gravity feed to any potentially piped sections of the bypass, in the catchment above the dam.
The outer race once operational will bypass the Phoenix Dam and direct the incoming water flows from the Bluejacket and Bungtown creeks directly to the spillway downstream of the dam.
Local rūnanga and Otago Fish & Game, alongside Port Blakely Limited have safely removed eels from the dam, due to the lowered level.
Separately work will be getting underway on the Bungtown race, and particularly the siphon, as the flow from the Phoenix catchment is insufficient to ensure continued supply to Lawrence.
The Bungtown race and siphon were constructed prior to 1900 and Council has sought approval from Heritage NZ before undertaking any improvement works.
Mr Witt said consent had been obtained from Port Blakely Limited to undertake the bypass works on their land.
The bypass is a temporary solution until the new Greenfield Bore (with water supplied from the Clutha River) is operational, which will supply the Lawrence township in the future.
This is under construction and involves the amalgamation of pipe networks with four pumping stations and a network of 48.5km of pipework. It is expected to be completed in late 2024.
The stage three water restrictions are still in place for Lawrence as a precaution as the demand of water to the township does play a part in the operation.
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.
The map below demonstrates where Bungtown Creek starts, north-east of the Phoenix Dam, roughly where the siphon starts and the point where the Bungtown outer race and Bluejacket Creek above the dam meet, before flowing into the dam.
