A Fine Dam Tour

It’s a cold, damp May evening and the TV weatherman has predicted a frigid southerly to grip New Zealand bringing the lowest temperatures of the year so far. Demand for power has spiked and all four turbines of New Zealand’s third biggest hydroelectric dam are cranking.

I’m standing in the control room, the nerve centre of the Clyde Dam, surrounded by huge TV screens with data, graphs and dashboards constantly flickering with real-time updates on the market demand and price for electricity as well as power generation and performance metrics from the dam.

Russell, our guide on this access-all-areas tour of the dam, explains that he’s never seen electricity demand come so close to outstripping supply, and with the weather bringing very light winds the power generated by the country’s wind turbines (approx. 5% of total generation) means that New Zealand is running very close to a power shortage.

Clyde Dam produces almost 9% of NZ’s peak electricity demand and this evening every watt, let alone megawatt, from the dam is needed.    

“That’s the challenge with renewable energy”, says Russell. “We’re subject to Mother Nature and the weather. Unless is windy, the sun is shining or there’s rain to fill up the hydro lakes then there’s no means to generate electricity”, he explains.

Russell, part engineer, part schoolteacher, part historian and 100% raconteur is a Clyde local and has been running tours to the Dam since they began. Constructed between 1977 and 1989, Clyde Dan was finally commissioned in 1992 and can produce 432 megawatts of power from its four huge turbine generator units.

Moving on from the warmth of the control centre and into the cavernous innards of the dam itself, Russell explains that over a million cubic metres of concrete was used in the construction of the dam with another 200,000 cubic metres for the powerhouse. It’s New Zealand’s largest concrete dam.

“The surface of the lake is 49m above us at this point, and 5.5m behind this concrete wall”, Russell gleefully explains as cold water* ominously drips from above and onto our heads, “and the dam is actually built in two separate pieces with a 2m gap in between”….

A 2m gap?... None of my tour companions seem particularly thrilled at this new piece of information given we are currently some 40-odd metres underwater!

*(Probably just condensation, according to Russell)…

At this juncture, clearly used to playing on visitor’s natural concerns about being in confined within the walls of a dam and underwater, Russell continues to explain that the dam is built on an active fault line! The Dunstan Fault.

“But don’t worry”, he chortles, “the dam is designed to withstand up to 10x the magnitude of any movement estimated at the fault – which would be greater than 7 on the Richter scale”.

Somewhat more reassuringly, Russell explains that there has been absolutely no movement in the dam since lake was filled.

Phew.

Less reassuringly, he then takes us to explore the Clyde Dam’s slip joint – a “floating plug” which seals the 2m gap between the two sections of dam.

“The slip joint is designed to accommodate any small movements in the fault without causing serious damage to the dam”, says Russell. “The slip joint is located directly above the fault and is sealed watertight by a concrete wedge plug, that’s held in place by the force of water behind it…”

“In the case of any movement in the fault, the main blocks of the dam either side of the slip joint are able to move, whilst the plug ensures the dam remains watertight”.

At this point, I decide to have faith in the science. And anyway, it’s impossible not to marvel at the cathedral-like grandeur of the slip joint’s construction.

Moving back to terra firma, the tour concludes in the powerhouse and a detailed examination of the turbines and generators. By now, it’s dark outside and it’s evident that we’re the only people onsite – other than the skeleton crew in the control room.  We all comment on what a rare privilege it is for Contact Energy to allow public access to this incredible facility on what has been a truly unique and fascinating experience.

At the time of construction, the Clyde Dam was considered controversial by some people, largely because it flooded houses and orchards upstream and the scenic Cromwell Gorge. We also learned from Russell that the dam has caused challenges for native fish species (especially longfin eel and lamprey) but Contact Energy - which operates the dam - have a dedicated native fish management project to support the upstream and downstream passage of these native fish. You can find out more about this project by watching this great video.

Today the Clyde Dam is an essential component of New Zealand’s infrastructure and on cold winter days it’s obvious that the dam is critical to help keep the country’s lights on.

Clyde Dam has also generated new opportunities for recreation and tourism including boating and fishing, as well as the development of the Lake Dunstan Trail, now one of New Zealand’s favourite cycle trails.