On Jun 29, 2004, at 8:00 PM, Tim Thompson wrote:
> Lyle,
> This might be a problem encountered at other dam sites -- comments
> from the list?
> The bases of the concrete dam and the crib dam behind it are buried in
> the
> inevitable wedge of sediment that accumulates behind dams. Based on
> borings, this
> sediment may be as much as thirty feet deep in places. Eventually,
> much of it would
> erode away, but we have to go ahead and remove the dams now, which
> means that
> we must also remove the sediment.
>
> Since the dams are nearly 900 feet long, doing test pits in this
> unstable sediment
> would not be an effective way to locate boats, or anything else
> trapped behind the
> dams. The sediment removal will be ongoing with the removal of the dam
> structures
> and I'll be monitoring this work to deal with anything that shows up
> as it progresses.
>
> I'm going to see if I can get some more info on the project web site,
> and will send the
> link to the list when this happens,
Tim,
Thanks for the update. Finding batteaux by test pitting is a very hit
or miss proposition, obviously, and to my thinking not at all effective
and huge time waster. And in that sort of my highly dangerous.
Hopefully you've got mechanical means of mud removal, and have mandated
them to be smooth buckets.
The boats we found in the Great Basin in Richmond had enough nails that
a magnetometer would find them, but again obviously not in 30 feet of
sediment within a river. More realistically within 5 feet. Some of the
boats had lined their fore and aft hearths with pigs, making
magnetometer finding somewhat more realistic, such that any large
signal would be worth having a look. Probing through the sediments
might work, but with a width of not more than 7 feet and up to 70 or so
feet long, probing is only viable for very, very close intervals, and
at not much depth. Another problem, even in the anaerobic conditions in
the Great Basin, some of the boat wood had the consistency of cheese
and others was tough enough to dull masonry blades. The final problem
is recognizing parts of boats. Current deposited boats lie in all sorts
of different directions, angles and positions. The Great Basin boats in
some cases had been truncated quite neatly, but no means could be
detected in the mud layers by which it happened. Basically, anything
that looks like two planks in proximity might be the slightly mangled
remains of a batteau. The later and larger freight boats and perhaps
packet boats with metal hulls shouldn't present a real problem of
identification.
Lyle Browning
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