Here are my observations on Cumberland bugs, gathered coincidentally over the past 25 years.
Midges hatch profusely year-round, most heavily just below the dam, diminishing gradually as you move downriver. Caddis begin showing up a few miles downriver, and can hatch in big numbers between Helm's Landing (5miles) and Burkesville (35 miles) from around Mother's Day until Flag Day. After Flag Day, Caddis hatches are increasingly sporadic until they pretty much disappear by Labor Day. Various broods of Baetis appear from early autumn until late spring, sometimes even into early summer. Size 16 to 20, depending on the brood. They come in waves. Like the Caddis, these bugs are largely absent from the first 5 or so miles of water, and are most numerous from about mile 10 to mile 45. This same stretch of water sees an excellent sulphur hatch beginning late May through July, most years. About a 16 or 18. Some years we will see Caddis, Baetis, Sulphurs and midges in a masking blizzard. At that time, just scream a wooly bugger through the middle of the mess and hope for the best. We also have good numbers of a Giant Stonefly, similar to the Western Salmonfly, Pteronarcys Californicus. Slightly larger, if you can believe that. I'm not sure of its correct taxonomy. However, it is very shy of bright light, hatches exclusively at night, and you never see it on the water in the daytime. So dry fly fishing this hatch is a no go. But all clean gravels have good numbers of the nymph, and the fish will almost always take a well presented heavily weighted black or brown stonefly, size 4 or so. We also see stray singles of a big (sz. 12) white bodied may fly, and when they are out, few fish will refuse your big Light Cahill or a House and Lot. Crayfish are common along the shelf rock ledges on falling water and fish love them. Never fail to fish streamers from a drifting boat. Thats all.