You said it while I was composing it in my head. Yes, fishing the fresh inflows—where the ditch meets the creek; where the creek runs into the reservoir—is a classic channel catfish scenario. The fly ought to be worth flinging to carp, too.A lot of worms would be washed into the creeks when we'd get heavy rain. Drifting a worm near the opening of a small creek would usually be rewarded with a nice fish.
One question about movement: do you see this as a static pattern, as in a dead-drifting, drowned worm? Tumbling in the current or retrieval action (in stillwater) will impart enough motion?
Would an extension of yarn or chenille—a free-moving "tail"—add anything besides hook-fouling potential?