Mickjoebill:
If it's underwater, and if the nose hits first, I'd expect the tail not to be buried. IIRC, tail is where FDR and CVR are mounted. (If wrong on location, apologies). By the time the wreckage hits the bottom, acceleration in the "down" direction would be pretty small. Granted, once in a bit of mud, sound of acoustic beacon pings would be muffled, no idea as to the dB loss.
How deep is the water in your consideration of "shallow water." (Muddy bottom granted in the area I think you are talking about).
Dozens of pages ago, a very succinct explanation was provided of how an aircraft at those speeds find hitting water a lot like hitting land, in terms of the decel at impact on the water's surface. FWIW.