Questions and Answers About The Opuha Dam Declaration of a ‘Dam Safety Deficiency’

 

RISK

What level of risk is there that the dam might fail suddenly?
All of the information we have points to this being unlikely. The nature of this type of incident is they tend to occur gradually.
While it cannot be entirely ruled out, the lowering of the lake level and the increased electronic real-time monitoring both lower the risk.
The construction of earth dams includes layers of defence designed to prevent sudden collapse.

What’s being done to reduce risk while the investigations are in place?
The lake has been lowered and is being continuously electronically monitored in real-time and daily onsite inspections.
We’ve engaged an international dam safety expert to assess the present level of risk, and advise on potential mitigation.

Should people be prepared to evacuate at a moment’s notice?
No.

How will warnings go out if an evacuation is necessary?
In the very unlikely event that evacuation is required, the public will be alerted through established Civil Defence procedures.

What evidence have you got that the risk of sudden collapse is low?
Dam safety experts with significant experience in earth dams agree there’s no evidence that the dam is at risk of sudden failure.
The dam is continuously monitored.

Have you alerted Civil Defence?
Yes we have alerted all our key stakeholders and shareholders.

Is it really safe for the dam to remain there, given it has breached already back 1997?
Yes. The dam breach in 1997 was a completely unrelated event caused at the time of construction. The dam was rebuilt and received a Code Compliance Certificate. The dam is continuously monitored.

What plans are there in place for emergency evacuation?
Emergency plans have been well-rehearsed with relevant authorities including Civil Defence, and the district and regional councils.
Civil Defence would lead the public notification and evacuation in the unlikely event of an emergency.

Will you be keeping everyone up to date on progress?
Yes – keep an eye on the website and Facebook page

Where can I get more information?
On our website and dedicated Facebook page

INVESTIGATION

Why are we being told about this now? Should we have been told earlier?
An engineering assessment was received on 26 September that prompted OWL to issue a “dam safety deficiency” notice.

What might have caused any internal erosion?
We have engaged an independent international dam safety expert to work with our own engineers to determine this.

What exactly is happening inside the dam?
We have engaged an independent international dam safety expert to work with our own engineers to determine this.

Could it have been prevented?
We have engaged an independent international dam safety expert to work with our own engineers to determine this.

Could it have been detected sooner?
Due to advances in understanding around internal erosion we are better placed to identify and understand this issue and are undertaking further investigations to get more clarity. The current dam electronic real-time monitoring is giving us continuous updates.

How was it picked up?
Our monitoring system picked up indications of a potential issue. We investigated further, including the latest Tonkin + Taylor report. This prompted OWL to issue a “dam safety deficiency” notice.

Will the independent dam safety expert and Tonkin + Taylor’s reports be released?
We will continue to provide timely and relevant information to the community.

Has the dam had any improvements since it was built?
Yes, continuous improvements and updates have been progressed based on engineering risk priorities.

WHAT’S NEXT?

Whose fault is this?
Our current focus is on the continued safety of the community via ongoing effective risk management of the Opuha Dam which is a significant community asset.

You said the water levels have been lowered, what does that mean for summer irrigators?
This might be a challenge but our priority is on reducing even theoretical public risk. We will engage with our shareholders and the Opuha Environmental Flow Release Advisory Group to determine the best course of action.

Is there likely to be any environmental impact on the Opuha/Opihi Rivers?
We will continue to meet our environmental consents.

With the lake lowered, is there any impact on power generation?
We don’t believe so. Power generation is a by-product of us meeting our environmental consents.