It's just the pressure in the pipes
If there's a big downhill run of pipe, and it blocks or if the pipe levels out downstream of that manhole all the water backs up.
You've got the pressure from whatever height of water until the next manhole upstream - which sometimes is considerable!
It happens in the UK quite a lot, but I don't think ever quite as spectacularly as that.
(
thistle, Sat 3 Jan 2009, 14:25,
Reply)
