I like that design. I think with a trash guard on the inlet to keep debris out, that it would work just fine. What type of valve did you decide on for the backside of the dam or have you decided yet? I would want to get one that can open up all the way so that I can periodically "flush out" the pipe to remove sediment, leaves, etc.

Water dries, rocks crumble, and trees die. The only thing that is eternal is the reputation we leave behind.
- Ancient Viking Proverb