Photo: Supplied / Clutha District Council
An Otago town's water supply may only have four to six weeks' capacity left with concerns about the remaining quality.
The Clutha District Council has applied for consent to divert a stream to bypass Phoenix Dam and ensure Lawrence's water supply, notifying the regional council last week.
The Phoenix dam was lowered by three metres as part of flood protection work that started last November, dropping to four metres as water continued to be pumped for the town's water before being bolstered a bit by recent rain.
Deputy chief executive Jules Witt said there was an inadequate supply for the catchment, creating a high degree of risk to the town's water supply.
"The urgency of this work is that we predict the bottom 25 percent of the water within the dam will be unusable because of poor quality," Witt said.
"It is also estimated that we have around four to six' weeks capacity remaining and it will be subject to incoming flows such as recent rainfall, which is why we need to get moving on the construction of the bypass."
The town is under stage three water restrictions to reduce demand as a precaution.
The council notified the Otago Regional Council on 9 April that work on the bypass would start immediately before approval under section 330 of the Resource Management Act 1991.
A map showing the intended work. Photo: Supplied / Clutha District Council
It included building a small temporary weir to help gravity feed any potentially piped sections of the bypass above the dam.
Once operational, water would be directed from the Bluejacket and Bungtown creeks to the spillway downstream of the dam.
"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 seven days, that the activity has been undertaken," he said.
The council had been formally notified by its landowner Port Blakely Limited about its plans to decommission the dam due to ongoing safety concerns about its age, Witt said.
It also included a plan of how to continue Lawrence's water supply.
Eels have been safely removed from the dam due to the low level.
The bypass was a temporary measure before they set up a new Greenfield Bore using water from the Clutha River.
Work is underway and involves a network of 48.5 kilometres and merging pipe networks with four pumping stations.
It is due to be finished in late 2024.
Located three kilometres away from Lawrence, Phoenix Dam was originally built around 1863 for goldmine sluicing.
A boil water notice for the Lawrence township is not connected to Phoenix Dam and is due to chlorine level issues at the water treatment plant.
Separate work is needed on the Bungtown race and siphon - which were built before 1900 - as the flow from Phoenix catchment isn't enough to sustain Lawrence into the future.