More subterranean fun (by )

A water expert came to look at our stream yesterday, for two reasons: the fact that water came through the wall of our house raises some worrying questions about the structural integrity of the tunnel the stream goes through under our garage, and up at the top of the waterfall, the raging flood eroded away some stones underneath a number of large heavy stones, and one day they'll come crashing down, possibly blocking the tunnel and creating a huge flood.

He turned out to be a really interesting guy, just as fascinated by underground stuff as I 🙂

Firstly, he examined the hole in our wall that the water had come out of, and peered into the tunnel from each end, and concluded that the tunnel was made from two dry stone walls - that is, piles of stones, without any mortar between them - with big stones laid on top. Over the centuries, water has squeezed through the walls of the tunnel and eroded the soil away on either side, creating underground cavities. When the stream flooded, the water pressure in there was sufficient to push away the last bits of soil connecting those cavities to the holes in our wall, and water came flooding through.

However, this will be very hard to fix. Most of the tunnel is beneath the garage, which has a poured concrete slab floor. And the tunnel is somewhat narrow to climb in, erect jacks to support the roof stones, pull out the dry stone walls, fill in the cavities, and replace the walls with something less porous.

The place where the water came out of our wall has a patch of lawn between it and the tunnel, so I may dig that out myself, just out of interest - it'd be useful to see just how undercut the foundations are, for a start.

But what the guy suggested was interesting. He said that making the tunnel able to withstand raging floods would be prohibitively expensive, so a much better idea would be to create a secondary route for the water. Namely, bury a 60cm diameter pipe running from just above the waterfall down across the drive, across the parking area, and into the pond behind the house. Two sluice gates at the top - one over the new tunnel, one over the waterfall - would allow us to control the stream, diverting the bulk of it down the new tunnel, while allowing enough over the waterfall for it to look nice.

That done, he could then divert all of the water via the new pipe while he climbed down into the old tunnel and lined it with concrete, thus stabilising it somewhat.

But having an extra tunnel would, as well as solving the problems, have several benefits:

  1. Underground tunnels are, inherently, excellent. The more of them we have, the better. Tunnels! Wow!
  2. While he had the trench open, I could lay a smaller pipe for cables, thus solving a long-standing problem I had: how can I get power and Ethernet from the house into the garden for wifi access points and garden sound systems, given that there's a drive in the way? I'd thought I was going to have to try and run cables up the existing tunnel, which would have been a harrowing task, and inferior to a dedicated cable tunnel.
  3. The new tunnel, being based around a plastic pipe, would be perfect for driving a turbine. He's said he'll design the bottom of it so that we could fit a turbine at a later date!

And a turbine means we could MAKE OUR OWN ELECTRICITY!

That's just too cool for words.


  • By Charlee, Tue 31st Jul 2007 @ 10:38 pm

    Yay 🙂

  • By Ben, Wed 1st Aug 2007 @ 7:38 am

    Can you get him to add an underground lab into the design? Then I think you'll have everything.

  • By David Cantrell, Wed 1st Aug 2007 @ 9:56 pm

    no no no no no, not an underground lab. He wants an underground lair. Labs have boring test tubes in them. Lairs have FRICKING LASER BEAMS and gigantic spiders.

  • By sarah, Thu 2nd Aug 2007 @ 10:01 am

    How did you lot find out about Alarics plan for a lair and mine for a lab?

  • By @ndy Macolleague, Thu 9th Aug 2007 @ 9:23 am

    Wow! Can you control the sluice gates via computer? Remote control waterfall. mmmm...

  • By Lionel, Wed 22nd Aug 2007 @ 3:59 pm

    About half a century ago your grandfather was keen to install a turbine. He followed up several ads in Exchange and Mart for second hand ones, but they were all bespoke systems built for a certain head and flow of water, so he never found a cheap one that matched what was needed, and ended up going for mains electricity. He was also keen to install a heat pump to take heat from the stream to warm the house. Cranham Mill was on a turbine in those days, and they left the lights on all day to provide resistance.

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