Another cross-post (sorry) - an interesting collection! Not clear if any 
archaeologists were involved though.
David

In the Londonist with a number of photographs

http://londonist.com/2012/11/in-pictures-the-new-river-tunnel-inspection.php
?showpage=7#gallery-1

http://goo.gl/J9joE

1,740 Tons Of Sludge: The New River Tunnel Inspection

By Lindsey . November 12, 2012 at 10:30 am .

The New River Tunnel in Wood Green was built in the 1850s to shorten the
route of Hugh Myddleton's original (1613), very loopy route and speed up the
"flowing reservoir" bringing fresh water from Hertfordshire to the city. The
1km long, Grade II listed tunnel between Myddleton Road and Alexandra Palace
is a fine example of Victorian brickwork and engineering.

The tunnel used to be inspected regularly by hard hatted folk aboard a flat
bottomed boat, but since health and safety concerns vetoed access on the
water, it was decided to drain the tunnel this autumn and give it a proper
clean out for the first time since it was finished in 1858.

Bowes Park Community Association trustee, Caroline Simpson, got some
fascinating insights into the process and some great photos from the crew
sent to do the very dirty job - it probably helped that she encouraged local
people to take cakes and buns down to them!

But what exactly was brought out of the tunnel? Caroline reports;

    Silt total 1,740 tons. Every ounce and pound shifted by hand. And over
the 154 years we also have: the two guns and two rounds of 'live' ammo',
lots of knives, five or six safes, lots of handbags and credit cards, two
motor-bikes, three bicycles, a skateboard, lots of kids trikes and scooters,
some imitation Swedish medallions(!) a 17th century pipe, two small Buddhas,
lots of plastic dolls, one antique white ceramic doll's head, a boat, a big
oak barrel and the old metal bridge handrail which must have fallen off many
years ago. The largest non-silt collection was bottles of various ages.

Happily, the tunnel's interior was in pretty good nick, only requiring minor
repairs and repointing. Those Victorians totally knew what they were doing.
As did the terrific Barhale crew who had to clear tons of sludge and rubbish
by hand so as not to disturb the roosting bats too much.

September 2013 sees the 400th anniversary of the opening of the New River.

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