Not sure this would apply to trout in a tailwater with the regular fluctuations that you describe, but there seems to be a longstanding belief that it's not worth fishing when the river is rising. Fishing when it is falling is generally considered a good thing.
Not being aware of the longstanding belief at the time, I went out and fished the South Fork of the Snake when it was rising noticeably for a number of days, and did quite well. When I mentioned that to one of the most accomplished fly anglers in SE Idaho, he mentioned the longstanding belief, and then he decided to give fishing on the rising river a go. I think he gave up the longstanding belief.
On freestones, during runoff, there are daily fluctuations, and probably more pronounced on some systems than you are describing. The fish still have to eat, whether the water is rising or falling, and you can still catch them if you go deal with what is in front of you. My bet is that those fish are quite accustomed to those regular, if somewhat dramatic ( to you ) fluctuations, and just keep on keeping on.
John
The fish are always right.