no, the water wheel wont back up the overflow. the open overflow falls to an open tray above the bucket wheel, fills the buckets as gravity does its work and pulls it down, rotating the wheel, then dumping it to an open bottom drain to the sump. zero back pressure. its an overshot water wheel. not a turbine that needs pressure and flow.
something midevil, like this
http://www.waterhistory.org/historie...aterwheel2.jpg
or this is better.
http://en.wikipedia.org/wiki/Image:O..._schematic.svg
simple , smooth, very efficient.