What’s under our streets (and why does the digging cost so much)?

This summer there’ll be roadcones, diggers and safety fencing aplenty in all Wellington’s towns, as councils dig holes to get the water (and poo) going where they should. So, what’s down there?

  • First off, it’s harder than you think to simply find where the pipes are. And that matters quite a lot (cos if the tip of a tine on your digger shovel accidentally punches through something….)
  • And then there’s knowing what they are – how old they are, what they’re made of, how big (and deteriorated) the valves and joints and seals are…
  • And then what other stuff is down there around them – what’s the soil, where’s the water table, what other cables or pipes or roots or building foundations or contaminated land or undiscovered historical artefacts are down there?

Discovering unexpected amounts of this stuff is a nightmare for infrastructure projects (check out its contribution to the little Petone-Melling pathway here.)

The fantastic George Street project in Dunedin have made this most excellent cross-section. The stuff in the key is pretty typical for a street that’s been there for a century or so…

a cross section drawing of what's under a street, with a big old pipe in the middle plus lots of other coloured cables - all sorts of utilities, plus a layer of road foundation and seal and little people and trees on top

And companies like Reveal are working away to map what’s lurking and working underground.

This is a bird-with-X-ray-vision picture of a bit of the central city… can you pick where this is?

on a dark background, a grid-like maze of red, green, yellow threads - which if you look closely are mostly following road lines of central Wellington. No key

This sort of stuff is what lets city authorities build accurate digital twins so you can get some glimpses of insight into the roiling complexity of a city – and the impacts of twiddling the metaphorical dials on things that we can control (landuse, traffic flow, people flow, etc).

At least, good underground maps and digital twins give us a chance of coordinating all the work of repairing infrastructure in an efficient way, like they did in post-quake Christchurch. Given how much machinery and how many people and how much gear it takes to upgrade a sewer line, and how much traffic management and so on it takes to do it within NZ’s health and safety laws (currently contracted out), any efficiency we can get is good!

But hey, surely it’s undercooking things to simply repair ancient pipes back to the standard we should’ve been maintaining for past decades … Maybe even we could start to think about building back better?!

Image credits:

  • Banner – Featherston St, January 2023 – Talk Wellington
  • Cross-section of George St – Dunedin City Council
  • Wellington infra map – Reveal

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