I am not familiar with the James river but I have fished by Dickson Dam a few times. Taking the fly rod I assume you are targeting rockies and browns. I have not heard of many browns now, since the flood but I have not fished it yet this year so that may have changed. Usually a few rockies around right out from the parking lot on the east side of the dam. I have always had my best luck with an indicator and a two hook setup, a small bead head, about 12-18" behind a san juan. Bead head in a red or pink has worked well, the san juan red or brown, most rockies hit the bead head. You will lose a few flies but try and keep your setup ticking the bottom most of the time. You can try the hopper dropper setup as well, keep the dropper at least 18-24" down, they may come up to it, if not you will have to go down to the bottom for them.
There should be lots of walleye around the dam this time of year, any leech or clouser pattern should work for them.
A couple pics right out from the parking lot
My son with a small brownie from a couple of years back