Bermuda Sod will fry in the heat with no watering, and it'll be lost money and lost effort.
I've had good luck with waiting till things cools off in the Fall, and getting a good stand of annual rye grass started first. Rye grass is relatively cheap in 50lb sacks at the feed store, and if covered with hay, or cheap erosion matting, you would probably get good coverage.
Rye tends to float, so some type of matting or netting is a good idea. If not, you'll have a beautiful patch of rye grass at the bottom of the dam.
How wide and tall is your dam?
