Thanks for that smurph, brilliant that they have kept something of historical significance.
Over here in W.A, it would have been scrapped, that's the mentality here unfortunately.
Back in 2006 at the time of closure there was a pretty loud cry from locals in Queenstown that they wanted it kept in place and preferably operating.
Even within Hydro, there was a lot of "what the hell are we doing to be closing this" and "we just can't let this happen" type thinking and that was at all levels from the top down.
So a way had to be found to make it viable and keep it operating. Financially it was a dud with very high maintenance costs trying to hold the old pipe together plus needing constant manning to run the station. That plus the risk was off the scale in terms of the reality that that old pipe was thinning out, leaking and in very pooe condition so could give way completely at some point. And that would have been a huge problem given that the only the only way to access the water valves (well, without using a helicopter) in order to stop the water flow involves going along the pipeline route to the dam, something that would be potentially impossible if the pipe had failed and was discharging at full flow into the bush. Even worse if it washed away the various bridges and walkway.
Solution:
1. Build a replacement pipe to avoid the huge maintenance cost and remove the risk of failure.
2. A small concession to modern technology via the installation of remote shutdown on the machines. There's still a need for manual start up and to change output but having the remote monitoring and automated shutdown means that it can be safely left running unattended once its going, thus removing the need for someone to sit there 24/7 watching over it.
3. Redevelop the lower station, this time with a machine of double the capacity of the old one so as to use the full amount of water discharged from the main (upper) station. That boosts revenue with higher production and the bonus that since it's completely new, it gets REC's on its entire output so brings in some $ that way.
From a technical perspective these days a steel pipeline would be the first choice. But there was a strong desire to keep the whole thing as original as possible, literally a "working museum" as it is often described, and so a new woodstave pipe was built. The only real hassle there was having to re-learn the skill of building a pipeline from wood but it was all done.
Wood was also used for the pipeline to the lower station for the same underlying reason. Keep everything as original as possible. And the extension to the lower station to accommodate the new machine is built in the exact same style as the original part of the building too (nothing fancy, it's just a shed really).
Another feature of the scheme is the walkway and "railway" that is still the only access to the dam. There's little carts that run along the rails, not an actual train, and some special materials carrying equipment was built specifically for the pipeline replacement project. See photo (pipe in the photo is the old one).
The dam wall itself was strengthened by Hydro (whilst still under private ownership) in the 1970's. They used as little cement as possible during the original construction in 1914. Firstly because cement was somewhat hard to get at that time apparently, and secondly because everything had to be carried to the site using muscle power only so they sure weren't going to use any more than they thought necessary at the time. Hence the need to strengthen it later but it's sound as such.
I'm still impressed at the efforts of those who built it all in the first place. No roads, no trucks, a very harsh environment but they got it done and a century later it's still in use.