12:02 Sep 14, 2011 

@Charles: Thanks for your note, Charles. I too did a search - both online and through my own reference material. Out of these three terms only "spillway" is used 'conventionally'.

Spillway and spillover channel are roughly equivalent, but I haven't encountered "spill drift" in any related context. And I'm not very hopeful now :-(

@Stephanie: Can't quote I'm afraid. The terms have been used synonymously. I'm just trying to check with a wider audience whether anyone had encountered 'spill drift' in the context of the other two terms (perhaps in some technical literature).

11:29 Sep 14, 2011 

It would be helpful if you could post a few full sentences as you seem to be saying that these 3 terms appear in sentences not as a list. Also, are you asking if they all mean the same thing?

11:05 Sep 14, 2011 

I have only encountered the term "spill drift" referring to the way in which a spill of some liquid (usually oil), discharged into a river, lake or sea, moves and spreads under the influence of wind and currents. But from the way you have expressed the question I assume this is not what it means here.

I can only speculate that if it refers to water that has spilled over the edge of the lake (as in "spill over" and "spillway"), it could mean drifting down sloping ground under the influence of gravity, or conceivably permeating the ground and spreading or "drifting" through the subsoil. But I have no evidence at all to support this. Let us hope that someone more knowledgeable appears.