Just thought you guys might be interested in this pic.
Cork City (Ireland) has a large network of tidal waterways in Culverts (large pipes basically) under the city. The city was originally on a network of small islands and during the 18th and 19th centuries they basically filled in and created culverts in the spaces between these islands creating main streets.
So, all of our main streets have at least 1, if not 2 or 3 of these channels running under them. They are not sewers and generally do not even connect to the surface water drains (there's a major risk of flooding if they're open as they can fill dramatically at high tide)
You can also see some exposed ducting under the street. Looks messy, but the older ducts you see crossing the culvert are pretty ancient.
Some of the culverts were opened and exposed (and inspected) during the city's recent complete replacement of drainage and sewage systems. The project went on from 1998 to 2005 (various streets closed to traffic for months at a time). The city's sewage system was centuries old and starting to become a major problem - collapsed pipes etc leaking their contents into the culvert system and into the river/harbour.
The various services : electricity, gas, water, telecommunications etc were all upgraded and replaced while they had the streets open and the city was given a full repave job.
The drainage aspect cost about €250m (about $336m)
Repave and replacement of services was quite a bit on top too. Pricey enough in a City of about 250,000 people. Well worth it though as the water quality in the river (and harbour) is now back to a level where it's even safe enough to swim in once more.
There's now a whole photographic archive, shows everything from viking house remains to victorian electrical systems.