A hammer, which is relatively dense, but small, should stay where it was dropped.
Don't be silly.
Do you really think that an event like that is incapable of moving a bloody hammer!?. Have you suffered a blunt head trauma in the recent past? You seem to be forgetting that in a flood lots of objects are all being swept up together. They are all going to jostle each other, with buoyant objects dragging along less buoyant objects and vice-versa. To suggest that a tiny thing like a hammer is going to somehow be immune to this chaos is, frankly, bonkers.
Given the right conditions just about anything can be dragged along.
Are you no longer standing by your original claim? The above statements do contradict each other. Just as food for thought, I found this image, of a boulder moved by a flash flood in Venezuela (taken from here).
No matter what you might say about hydrodynamics and surface area, it should be obvious that a force of nature capable of moving this should be capable of shifting a few hammers.