RobA- By the lack of response so far, I think that gives a good indicator that overall everyone feels that trees on the dam, no matter where, is probably a bad idea. I will say from my experience with our trees on our farm, which used to be a nursery, that norway spruce(with colorado/blue spruce as a close second) has pretty shallow roots. They normally don't have a tap root that goes deep like other trees. They will often blow over because of this when you get heavy rains and high winds. I still would not put these near any drain pipe, because roots will get into those and destroy their purpose.
Have you considered other options like a decorative fence, etc?
