Here is a link to a calculator I made a while ago to give you an idea of which ramps on Allatoona are open, and how much water they have. Of course, this information is based on the accuracy of the COE's ramp elevations. At 3 feet, the Corp closes the ramp (well, that is their policy at least) so that is when the calculator calls it closed.
Its more to give you an idea of how much water is there. Check it out and let me know what you think!
http://allatoonainfo.com/boatramp.htm