Thebar...
A couple of suggestions:
First, I would check with the TN DOT to find out what they use on steep grades in your area. We use fescue in Missouri, but those guys deal with steep roadside grades on a regular basis and would be able to tell you what does a good job of growing and holding down erosion in TN soil...and as CJB noted above, you want to add a nurse crop that will sprout quickly to hold the soil until your annual plants take hold (like rye or oats in my area, but again, I would check with TN DOT to see what they use on roadsides). I would stay away from highly invasive plants. They do a great job of holding the soil, but will spread to unwanted places and are hard to eradicate (think Kudzu in your area!).
Second, I would suggest putting down some jute netting after you seed, especially if your grade is steeper than 3:1. It doesn't take much rain to cut sizable chunks out of your dam's backside. There are many types of this material, but it acts to hold the bare soil for a couple of years until your plantings catch hold...it decomposes after a couple of years. I have attached a link for Dayton Bag & Burlap...I got my netting shipped from their Chicago location and it worked great.
http://daybag.com/info/locations.html
