I have been fishing the area you are in for many years especially a creek that flows into the Pedernales just a mile or so downstream. Here's my thoughts. You probably won't have much luck catching shad at that area of the river. I could be wrong, but I haven't observed them there. The very best bait for bass there is a live bluegill. The bigger ones catch the bigger bass. I fish them about 3 feet under a bobber with a small pinch on weight to keep them off the top of the water. The best catfish bait I've ever used there is a big old yellow or green grasshopper. They can't resist them. The river and surrounding creeks have many spots where the water has undercut a ledge in the surrounding caliche stone. This is an excellent spot to fish next to especially in the summer when the cool shade attracts the fish. The low water dams are excellent places to catch catfish, especially at night. Go down to one at night with a flashlight and flip it on. You'll see them stacked up below it waiting for a meal to come over it. Good luck and welcome to the forum.
now I never would have thought to fish the down stream side of a dam. just figured it would be too shallow and too choppy for the fish but now that I think about it, it makes lots of sense why they'd be there.
for catfish would standing on the dam and letting the current take a bobber, swivel and short leader downstream be a good option to try?