I am a confirmed Lake Powell fall fisherman. I've had more good days in the fall than in the spring. The one thing you need to know about fall fishing is that you need to be flexible because the patterns can change daily.
Generally speaking in the fall shad migrate to the backs of the canyons and coves and the gamefish, stripers, smallmouths and even walleyes, follow them. So in most years fishing in the backs of canyons and coves is generally more productive than fishing main lake structure. However, that is not always the case. I usually start out by following this traditional pattern, but if I'm not catching fish I change. Most of the time I'm able to figure out where the fish are and what they're doing. Since I'm a smallmouth fisherman, that's the species I normally target, however if I can't find a consistent smallmouth pattern I may look to stripers, especially if I'm seeing big schools on my graph. Having a rod rigged with a jigging spoon up on my deck has saved a number of fishing days for me. If there has been extended cold weather and I'm convinced the smallmouth bite will not be there, I often go looking for stripers from the get go. I know that in the late fall I can usually go into the back end of Gunsight near the forks or the back end of Padre Canyon and find two or three schools. This is my ace in the hole if smallmouth fishing is slow.
As to what to fish with, you need to let the fish tell you that. If you see shad schools on the surface (they look like riffles) or physically see game fish busting the top then using surface lures and even lipless crankbaits are a good idea. If I don't see any surface shad or gamefish activity, most notably when smallmouth fishing, I stick to the tried and true drop shot technique with soft plastic baits. You need to learn to recognize what the fish are doing and taylor your presentations to match that. It's not something I can describe here. It just takes practice.
For fall smallmouth most folks would believe shad imitators are generally the best lures, however I've seen years when shad were in abundance but smallmouth stomachs were crammed full of crayfish. I have years when I knew bass were feeding primarily on crayfish but preferred a shad imitating lure over a crayfish pattern. Go figure. As Wayne says, fish don't read textbooks, and that's particularly true in the fall.
As for depth, I've caught smallmouth all over the place in the fall both shallow, deep and in between - and all in the same day. Last week my friend John Conrad and I caught a tremendous number of smallmouths, most of them at 10 to 15 feet. However we caught fish, and some very good ones, as shallow as five or six feet and all the way down to over 30 feet. That's why I like to fish the drop shot so much. It enables me to fish a big swath of the water column with the same rod. That is particularly true in the fall.
My general rule of thumb for fall is start in the backs of the coves and canyons as that is where the most catchable fish are likely to be. If that is not successful be prepared to head out to main lake structure. If an area isn't producing, move. Have rods rigged with drop shot setups, jigs, surface lures, crankbaits and spoons ready to go, and let the fish tell you where and how to fish. Hope this helps.
Ed Gerdemann