Need advice on deep silt searching

[NeesiePie]

I'm part of a small, grassroots archeological organization that's planning an expedition next spring. Because of our budget we can't hire professional SAR divers. We will be searching a pond that's a couple hundred acres by about 10 feet deep, with silt up to 3 feet deep in many spots. The makeup of the pond bottom is highly magnetic, and most of the objects we're searching for are not, so hand-held metal detectors are of limited use. Because of the archeological nature, we can't just drag or dredge the pond. I know the best way to do it would be to set up a grid system for a meticulous inch-by-inch hand search, but we don't really have the time or personnel to cover such a large area that way. Any suggestions on other tools/methods we might employ to have some chance of finding something? We'll be fighting silt-outs, bad weather, and cold water, so anything to make this process more time-efficient would be helpful. TIA for any advice!

 

[Johnoly]

..most of the objects we're searching for

Is the size of the objects like a basketball or more like candy bar? Any time you are searching it's always a balance of time vs money and to be successful you need to spend ALOT on one to reduce the other.

 

[boulderjohn]

You won't want to read what follows.

I had a student who came to me for almost exactly the same purpose you are describing. I taught him to use a drysuit, to have excellent buoyancy control and non-silting kick techniques. It took a few years, but by then he was looking really good. He was even cave certified. He set out on his original goal (in Yosemite National Park).

To cut to the end of the story---he gave up.

 

[ofg-1]

Get in touch with Fisher or Edgetech ans see if you can lease a sub bottom profiler or if they know of a company that will rent one with operator.

 

[Celt]

Clearing 3 feet of silt from a few hundred acres under 10 feet of water would be a mammoth task. So you have to approach it very like a test trench on land. First you need a lead in. A point on the shore with an area of interest to your search. Drive 2 large pegs 4 feet apart on the shore and 2 more 30 feet into the pond 2 feet above the silt. Run a strong line between them marking off the search area. Search along the rope with a heavy round bar, the sound off rock, metal and wood is different underwater. When and if you find something of interest you’ll have to place a coffer around the object and pump it out with an air lift, make sure to screed the sediment in case there’s material of interest coming up the lift. A pontoon 16x16 is handy for working the lift.
P.S. the coffer only needs to be a little higher than the silt it’s keeping out but heavy enough to stay in place.