There has been some discussion on hydrodynamic forces as cause for apparent damage.
By way of a reminder I would say that my understanding of hydrodynamic force is the forces acting in fluids in motion and not objects that impact fluids such as water. Accordingly unless someone pulls a stunt such as flying into Niagara Falls at their full fury then the question of hydrodynamic force does not really come into play.
The damage sustained to an aircraft impacting against any surface is caused by the dynamic force of the travelling aircraft and not by movement of the surface or depth of the water.
In this instance my money is on the in -flight loss of the empennage as a result of aerodynamic forces imposed upon it beyond its structural limititations.