I have been up and down the river from Louisville to Markland and I am pretty sure there is not anyplace much deeper than 35 feet at normal pool. Now, the rock quarrys that they opened to the main river can be really deep, some of them are 65-70.
From what I have seen, most of the river bottom is silted in and mostly mud. BUT, there is areas that can be more rocky or at least gravelly. My theory is look at the land around the rivers edge and it will give you good idea of what the bottom is like.
There is areas of the river that have "washouts" or ditches that dump rock and gravel out and make a "harder" bottom.
I also believe you may find anything at the bottom of the river----logs,rocks,cars,boats,building remains, etc. etc.