squeeky,

I think that makes a lot of sense. I recently was plagued with leaks in an old dam that were caused by a combination of animals (beavers and/or nutria) and tree roots. The leaks manifested themselves at the base of the dam on the backside, but repeated attempts to repack those areas failed to stop the leaks. Finally, I decided to go up to near the top of the dam and dig out all the way down to the base...it was there that I found the real source for the leaks (cavities left by animals and tree roots pulling water from the pond). The water was simply gravitating down to the base level and exiting there. After digging that out and repacking with clay, problem solved.

I think tree roots cause much more problems than we realize. These were trees that were not on the dam but behind it at the base. They had sent roots well into the dam to those cavities and were pulling water out. Not only are trees on the dam problematic, but trees near the base also can cause problems....especially when coupled with animals burrowing.