smhog,
That's a difficult question to answer without more info.
My concern would be that nearby creek, when that 100 year flood of water, which happens every three or so years it seems, comes roaring down your area. Will a pipe protect your dam? By itself, I doubt it.
You need to have emergency spillways, regardless. Overflow tubes can be underdesigned, can clog, and can otherwise fail, so always have emergency spillways.
I assume the "tube" you are talking about is a pipe that will go through the dam structure and remove excess water. That is a common approach, but I personnally do not like it....pipes fail, can compromise the integrity of the dam, can leak, require constant attention to make sure they are open, and are expensive. I prefer natural spillways, if at all possible, i.e. an escape for overflow water that flows across undisturbed ground. I have ponds that are as old as 75 years with nothing but natural spillways that have never had any problems with dam integrity. A natural spillway can be designed to handle tremendous volumes of water. There can be a situation where a natural spillway is impossible, but that is very rare indeed.
