I don't think river birch tree's are a good choice. That's a weak tree. They are alway's dropping limb's and leave's. They also die young naturally and you will get the blame. The time to plant tree's is in the dead of winter so you have that working against you. I know this is all negative but i repeat. - I don't think river birch is a good tree.
Some info - http://www.na.fs.fed.us/spfo/pubs/ho...h/ht_birch.htm