What makes a dam?

The Waimea Community Dam has provided some unique challenges but also some great opportunities to those involved in its construction.

Civil engineer Richard Greatrex is the dam’s construction manager and engineers’ representative. Prior to taking on this role, he worked on several major transport infrastructure projects around the country.

“It was a great opportunity to combine previous experience I’ve had doing major infrastructure projects of this sort of size with my interest in dams,” he said. “Roads are very good training grounds for civil engineers because, much like dams, they require coordination of lots of different aspects.”

Greatrex oversees specialist contractors who do drilling, waterproofing, and linking the dam to the outside world, who then work alongside Fulton Hogan and Taylors Contracting and their subcontractors to construct the dam.

There are also engineers across multiple disciplines doing work in the geological, structural, hydrological, mechanical, and electrical fields.

“Dams are pretty interesting bits of infrastructure for civil engineers,” he said. “One of the great things about dams is the multidisciplinary nature of them.”

Major geological challenges were presented during the construction of the dam with the quality of the rock found onsite being poor and shear zones intersecting crucial locations of the build.

Greatrex said one of the most difficult factors was a shear zone being present at the top of the spillway, the great slide from which excess water will spill over, allowing the Lee River to continue flowing.

“By the time we found that shear zone, we were committed to the spillway alignment because we had already excavated and started construction at the bottom.”

He said their options were to stop the project while that issue was sorted out, or to re-sequence the build and get enough of the design information out early to allow construction to progress.

They opted for the latter.

“It was a close-run thing whether or not we’d be able to make all those changes and deliver them with confidence ahead of the construction starting. That’s difficult.”

But after a “sterling effort” from those working on the project, the shear zones have been addressed and the spillway is nearing completion.

“It feels really satisfying to look at that spillway today and see that we are very close to finishing.”

The Waimea Community Dam is the first publicly-funded dam to be built in New Zealand for more than 30 years since Otago’s Clyde Dam was commissioned back in 1992.

“That’s a couple generations of engineers and contractors passing through,” Greatrex said. “This project is providing opportunities for the next generation of engineers in New Zealand to build dam engineering skills that might otherwise be lost.”

Many people who worked on the Clyde Dam have been pulled out of retirement to give advice on the project. The Waimea Community Dam’s principal geologist was even a graduate geologist on the Clyde Dam.

“It’s been great on this job, we’ve had some very experienced people who’ve been able to come onto the project and provide that experience and insight, and pass it on,” Greatrex said. “This project is delivering not just for Nelson-Tasman, but for the country.”

The dam is expected to provide water security to the area around the Waimea Plains for the next hundred years or more.

“We are building a high-quality asset that is going to last the distance.”

Construction figures:
- 53 metres high, 220 metres long
- 150 workers during the construction’s peak.
- 3,000 tonnes of reinforcing steel used.
- 25,000 tonnes of sand imported.
- 32,000 cubic metres of concrete used.
- 110,000 cubic metres of drainage rock imported.
- 490,000 cubic metres of rock used.
- 13 billion litres of water to be held in reservoir (5,200 Olympic-sized swimming pools worth).
- 17 kilometres of holes drilled for waterproof grouting.
- 164-metre-long spillway.
- Spillway can handle 1,058 cubic metres of water per second (almost an Olympic-sized swimming pool worth of water every two seconds)
- Longest concrete slab formed over 50 hours of slip-forming.
- 40,000 trees planted on Rough Island to combat emissions.

Public Interest Journalism funded through NZ On Air