Iv'e often thought about that myself nobby, and I've been at it for years.
I have plummed a lake with a waggler (light float) and got an even depth of about three feet all over.
However, when I had to wade into it one day, the depth was up to my shoulders, and I'm six foot.
Before I go any further , welcome to the best Angling site going. Somebody is bound to make the remark, I didn't know they piled shit that high.
I think its right to say silt vary's in density, from a cloud to mud. The fish will find the bait no matter what it is.
Appart from getting in the water , I don't know that you can find the depth of silt, but maybe somebody else can tell us otherwise.