Opuha Dam Remediation

Opuha Dam
Location: South Canterbury
Duration: 3 Months, 2006
Client: Network South
Value: $2.2 million
Delivered on Time and Budget?  Yes

The Opuha Dam is located on the Opuha River, near Fairlie, and has an embankment 50m in height which stores approximately 95 million m3 of water for irrigation and hydro-electric generation.

Revised Dam safety regulations required the excavation of the downstream shoulder face and replacement with coarse aggregate. Also required was the excavation and installation of filter materials along the existing dam crest at each abutment.

The crest and abutment tasks were extremely technically challenging as they involved high quality work in a confined area, using trench shields and specialist equipment to prevent material segregation during replacement.

The downstream face remediation required excavation of 15,000m3 of existing material in a stepped process and then replacement with coarse gravel and boulders back up to the original profile.
The work was extensively monitored full-time by an onsite Designers representative and both remediations were successfully completed while the dam was still in full operation, supplying water and generating power.

A 1 in 100 year snow event during construction caused major access and stone placement difficulties but the project was still finished ahead of programme.


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