If you assume a 'successful' ditching, there would be very little actual debris - basically one really big piece (the aircraft), and some smaller pieces such as the engines and control surfaces. The engines are heavy and would sink straight away, the aircraft itself might float for an extended time (depending on the degree of damage from the ditching) but would eventually sink leaving little if any trace. The wild card would be the control surfaces that ripped off during the ditching - they are lightweight and could float indefinitely.
Which, interestingly enough, is exactly what we currently have.
I quibble with the word "exact"
We only have one piece of control surface and it could have departed in any number of ways.
Now if we find more surfaces like this than maybe we have a hint