Weeks of water left as dam set to close

The Phoenix Dam is set to be closed. PHOTO: SUPPLIED
The Phoenix Dam is set to be closed. PHOTO: SUPPLIED
Lawrence has between four and six weeks of water supply left as a race against time begins to construct alternative sources — including using a century-old race to send water to the town.

The town’s water source Phoenix Dam is set to be closed because of safety concerns and the new source is months away from operation.

The Clutha District Council released a statement yesterday saying it had submitted a consent application to the Otago Regional Council to divert the stream above Phoenix Dam and form a bypass to ensure the supply of water will continue for the West Otago town.

Council deputy chief executive Jules Witt said there was 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 continued to decline.

There was a boil water notice in place for the Lawrence township but it was not related to the issue with the Phoenix Dam.

Flood protection work to lower the level of the Phoenix Dam involving a controlled dewatering operation began in November last year.

The flood protection work involved lowering the level of the dam by 3m by way of a siphon system and was achieved at the end of January. The dam has now been lowered to 4m as water continues to be pumped to provide the town’s water supply. Recent rainfall has lifted this level back to 3.5m.

Mr Witt said the council had been formally notified by Port Blakely Ltd, which owns the dam, of its intention to decommission it due to ongoing safety concerns related to the age of the dam. The dam was built in 1863 for gold mining sluicing.

"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", Mr Witt said.

"It is also estimated that we have around four to six 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."

As a lifeline utility, the council has the ability to undertake the required works under emergency provisions.

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.

Eels have been safely removed from the dam.

Separately work will be getting under way 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.

The bypass was a temporary solution until the new Greenfield Bore — with water supplied from the Clutha River — was operational, which will supply the Lawrence township in the future.

The bore, with a network of 48.5km of pipework, is expected to be completed later this year.

The stage three water restrictions were still in place for Lawrence as a precaution as the demand of water to the township does play a part in the operation.

— Staff reporter