They Found a Fault Line… Halfway Through Building This Dam

Added: 2026-05-17

[00:00:04]And the poor old dam.

[00:00:20]Good morning. Welcome to the Clyde Dam.

[00:00:24]102 m tall, the biggest concrete gravity dam in the whole of New Zealand. The project to build this was nearly abandoned when it needed further stabilization and it flooded an entire town. And today I'm taking you inside it. So, I've had to voice this over because I was on a tour with several other people and I wasn't able to walk around and give a running commentary as we went sadly. Um, so a little bit different from normal, but this is a dam 490 m long, 102 m high, 70 m wide at the bottom and 10 m wide at the top. This is looking down onto the powerhouse where there are four main turbines. And these are the pylons that take the transformed electric out uh into the main New Zealand grid. Uh the one on the left goes south and the one on the north goes right. Um the pen stocks you see below are 7 meters across. We'll see more of those in a moment and uh they are constantly full of water. This is the main Cluther River. Uh the Kufa River is over 300 kilometers long and uh is the biggest flow of any river in New Zealand um including the Wicato uh which I think is on the North Island. Um so yeah, so this is the dam uh looking down the river.

[00:01:51]These are the main slle gates which we'll talk about more when I shoot them from below. Uh and firstly our guide took us in this way through the security gate. Kim at Clyde Dam Tours was brilliant. So if you are in the area and you are thinking of doing a dam tour, I'll put Kim's details below. She's very knowledgeable lately. Um knew all about it. Was able to answer pretty much everybody's questions. Here we're going into the control room. Now, the control room was the only area we weren't allowed to film, uh, sadly because, uh, obviously there's a lot of sensitive information in there. I was actually really surprised that we were allowed to film as much as we were throughout the whole of the, um, the whole of the site.

[00:02:35]But the control room was really interesting. They control three dams from in there. This dam, the Roxer dam downstream, and Lake Hawaiia dam upstream. And they also sell the electricity straight into the national grid from that control room. Uh, weirdly there were only ever, well, there were only one stroke two people on duty when we were there. So, it really, as a general rule of thumb, doesn't take uh many people to run not just this dam, but all of the dams uh that it covers, which is quite incredible. Um, one guy had his dog in there and uh they've got weights and running machines, etc. This gives you a good idea of the pen stocks.

[00:03:17]These are two spare ones that were built into the dam when the dam was built, ready for future use. I'm told they will never be used um for whatever reason. Um but you can see the size of them and the amount of water they would shift.

[00:03:33]>> If you got this if you got this far through the video, thank you very much for sticking with it. Hope you're finding it interesting. Give it a like for me, please. And if you're on a mobile, hype it. Uh, and if you think you might like my other content, have another look through the videos and be so sure to subscribe. Now, we were brought into the galleries. There are three galleries, I believe. A higher one, the middle one that we're in, and a lower one. Those gray things on the wall are flood defense panels.

[00:03:59]In 1990, I think it was, there was a major flood on the Cluther River, and the control room and the powerhouse came within 4 mm of being flooded and put out of action. And uh these are mitigation measures that were added after that flood to protect from any future flood that might take place.

[00:04:20]Um the galleries are obviously built into the concrete dam and are used for inspecting inside the dam and for monitoring seepage and movement which you'll see in a moment. Um there are other corridors that go off them. And on the left hand side, if you look in the floor underneath that wooden boarding, is drainage that allows some of the seepage from the dam to uh to drain away.

[00:04:47]Um not sure quite where this corridor went, but there were various of these um corridors that went off in different directions. You wouldn't imagine that a dam like this would seep, but there is seepage, which is quite incredible.

[00:05:02]Uh on the right here, there's another corridor leading off. And then you've got the lift shaft. This goes from the top to the bottom of the dam. Um and came within millimeters of being flooded as well in the 1990s flood, which is what Kim's explaining to us here.

[00:05:18]Uh and had the power gone out, that was the only way anybody could get in and out because the main road into the dam had been um completely washed away and flooded. Now, behind this wall here, uh you'll see from this sign, 5.5 m behind this wall is Lake H is Lake Dunston. Uh and it's 49 m above this point. So, it's quite an eerie feeling. As you can see looking down these corridors, uh they go on for hundreds of meters.

[00:05:50]The dam was poured in uh different concrete sections. Here you can see the joint between different sections, which is obviously numbered. And this is a copper earth strip for lightning strikes etc. And there's one of the seepage holes.

[00:06:05]This uh this item monitors the movement in the dam. It's like an upside down plumb bob. So if there's movement in the base of the dam, the top moves even more and again is monitored from the control room um should there be any movement in the dam. And you'll see from this next clip, uh, there is a graph there of the dam movement over the last few years.

[00:06:30]Um, more shots down the corridors with the drains in the floor and another shot of the poured concrete areas.

[00:06:42]This is looking down a shaft into the lower levels. We were told it was about 30 mters, which would be about what 90 100 ft I suppose. Um, we weren't allowed to go down there, but you can see how deep it is with the water flowing at the bottom.

[00:07:04]There are lots of areas in the dam that you weren't allowed to go and look at, but equally I was quite surprised by the access we were given and the fact that we were allowed to film so much of it considering it's critical national infrastructure. Here you can see the pen stocks. They get narrower as they get near the turbines. I'm told they can take the full flow of the Cluther River.

[00:07:26]So um the normal flow of the Cluther River, not in flood obviously. and they narrow down nearer the turbines to build the pressure to turn the turbines. Here are the huge slle gates. They weigh tens of tons each, size of a house, and would take several minutes to open fully. Um, and you can see here what they're like in flood uh when the dam is um open to allow excess water off. Now, here's the interesting bit. These concrete slabs are open to the water below. And you'll see as I pan up, there's a gray line right the way up the dam. Now, this is the Dunston fault. When they were building the dam in the 1980s, they discovered a fault line which was initially thought to be inactive, but then decided it was active. And they had to come up with an engineering solution, which meant the dam couldn't be solid because obviously if it was on an active fault line and the fault moved or there was an earthquake, the dam would crack and potentially completely fail. So, they came up with the idea of basically putting a great big line right the way through the dam. And as you'll see what Kim's doing here, the dam is the two white boards and the blue block is a concrete plug that just plugs the end of the dam up. So that plug is kept in place by the weight of the water from the lake which is 26 km square kilm and holds 430 million cubic meters of water.

[00:08:54]that keeps that weight against that block. So, if there was any movement, the dam can move, but the block would stay in place. Now, it's not to say that if that happened, they wouldn't have to drain the lake and do some works, but it would mean not a catastrophic failure of the dam. It is believed that the Dunston fault um is likely only ever to give an earthquake of seven 7 and a half magnitude maximum. Um so, one has to hope that they're right on that one.

[00:09:23]There were also a lot of land slips uh in Lake Dunston or around Lake Dunston that had to be stabilized to prevent a land slip occurring and over topping the dam.

[00:09:36]This is looking at the plug at the end of the dam. So this huge 2 m gap runs right through it to the plug at the end um which is literally kept in place. And there you can see looking down if you were looking down on the top of the dam what the plug would look like and how it's kept in place.

[00:09:55]And this is looking down into the depths of the dam with that plug in front of you.

[00:10:03]So yeah, it's quite um an amazing feat of engineering to find a dam with this huge 2 m gap running through it and then just a what you'd consider to be a fairly small plug of cement. There are pressure release valves here for any water buildup um inside or around the plug so that they can release the water pressure.

[00:10:24]Then we were brought into the powerhouse. Now the powerhouse is just enormous. There are workshops etc. Um off of it there's a huge gantry cla crane there that you'll see above my head that I'm looking up at. Um but it's the size of a cathedral. As I pan round, you will see the sheer scale of this building. Now, the transformers and the uh turbines are below deck here um behind those orange barriers, so you don't see them from above. But the whole place is well organized, spotlessly clean, painted floors, you know, really um really smart and well looked after and clean. This is looking down on top of one of the turbines. Um, below that, uh, shelving is the actual part that generates the electricity. Um, the dynamo, I suppose you'd call it. And here you can see Kim is demonstrating from a model of what actually sits underneath that metal shelving. The rectangular bit at the top, which you'll see start to spin now, is actually what generates the electricity. And that is only, you know, a foot or two below the paneling that you'll see me standing on in just a moment. There you go. So, I'm standing on top of a top of the electrical part of the transformer.

[00:11:46]Then, we were taken down two levels. So, you go down two levels. There's a plaque telling you exactly what the turbines uh and the generator does and is. And we were taken down two levels to the lower levels and eventually into the turbine.

[00:12:03]Now, sadly at this point, Kim was telling us all about what happens here, but it is so loud and I can't hear in noisy environments at the best of the time. So, without going right up to her, I couldn't hear. But you'll now hear in a moment um when we get near to the actual generator and the turbine, you'll hear how noisy it is because I'm now going to leave that on for you.

[00:12:42]Heat up here.

[00:13:08]There you go. You could hear quite how loud that turbine was and why I couldn't hear exactly what she was explaining.

[00:13:15]This is where the water comes out from the turbines uh back into the Cluther River.

[00:13:21]And as I pan around, you will see the transformers that transform the power up and pop them into the grid.

[00:13:27]So there you go. That was um that was inside the dam. Sorry I've had to voice it over, but I hope it's been uh interesting for you.

[00:13:35]So there we go. What do we think of the Clyde Dam, the biggest concrete gravity dam in the whole of New Zealand and separated by a fault line running right through the dam.

[00:13:50]I really enjoyed making this video. I hope you've enjoyed it. you might like this video that I'm putting up at the end uh which is of a road trip I did right around Invarill and Bluff. Thanks very much for watching and I'll see you on the next video.