Phoenix Dam bypass

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 dam is owned by Port Blakely Limited. Port Blakely consider themselves to be a values-driven, family-owned forestry company built on a century of stewardship. They own and manage forestland in both the North and South Islands and have owned this land since 2019.

After receiving advice from experts, Port Blakely made the decision to lower the level of the dam to ensure its ongoing safety. Since then,

The dam has been assessed as having a high impact classification under the Building Act 2004.

The dewatering operation is being undertaken to significantly reduce the impact of any risk of potential failure.

Lawrence’s water supply comes from Bluejacket Gully creek, which is fed from the dam, with a resource consent being held by Clutha District Council (CDC) for the damming of water. CDC is also involved from a civil defence perspective given the dam is situated above the Lawrence township.

The plan going forward is to divert the stream above Phoenix Dam and form a bypass to ensure the supply of water will continue for Lawrence.

CDC has previously commissioned safety inspections by Opus (2006) and Riley Consultants Limited (2021) to identify potential dam safety deficiencies, condition issues, and areas of uncertainty with respect to the dam.

Riley was commissioned by CDC in early 2023 to complete a Potential Impact Classification (PIC) assessment, and then later by Port Blakely Limited to carry out preliminary investigations, including 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 2004.

You can read more about new dam safety regulations on ORC’s website and MBIE’s website.

Using a controlled emptying/dewatering operational plan to lower the level of the dam by 3 metres, by way of a siphon system.

The water is 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 was installed, along with flow meters to monitor the water flow.

The level of the dam has been initially lowered by approximately 3 metres. This will lower the level to hold around 75,000 cubic metres of water.

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.

A Freshwater Ecologist Assessment was undertaken and the effect of lowering the water level on fish is expected to be limited to the resident brown trout and possibly longfin eels.

Local rūnanga and Otago Fish & Game, alongside Port Blakely Limited have safely removed eels from the dam, due to the lowered level.

Previous assessment reports commissioned by CDC assessed the dam at a lower risk. However, recent deterioration of the dam has signalled the need to do the dewatering work.

Modelling based on the lowered level of water is underway by EMO and the report will be provided to the community and other stakeholders when available. The modelling identifies how people, houses and businesses may be impacted in a flooding event. Live monitoring continues with key stakeholders having direct access to up to the minute alerts.

Residents would be alerted by emergency services and/or an Emergency Mobile Alert. We recommend community members are prepared at all times for any emergency event. https://getready.govt.nz/en

Seepage is the term given to water exiting from a dam’s embankment. All dams have some seepage as the impounded water seeks paths of least resistance through the dam and its foundation. Seepage should however be monitored and controlled, to prevent erosion of the embankment or foundation materials or damage to concrete structures.

Overtopping flow occurs when a water detention structure (such as a dam’s) capacity is surpassed, and flow passes over the structure. Any water exiting the dam from the top of the embankment is known as overtopping.

Council understands that it has been seeping for some time and visual assessments were being done to monitor it.

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.

Under Stage 3, hosing is only permitted once a week between 8pm and 8am, other than this a ban on handheld watering and hosing is in place. Sprinklers and irrigation systems are banned. Please avoid washing cars or boats while under Stage 3 restrictions.

Thanks to all of those that are already doing their bit to conserve water this summer.

Work continues on the Greenfield Rural Drinking Water Scheme Project, which involves a new water source and construction of a 48.5km pipeline from near the Clydevale Bridge to Lawrence. This project will improve the quality of drinking water and the reliability of supply to the Balmoral, Tuapeka, Waitahuna and Lawrence water schemes. It also has additional capacity to futureproof water supply for the area.

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.

It is expected to be completed in late 2024.

No. We advise people avoid the area due to health and safety hazards.