After exiting The Fractured Drain back into The Barren Aqueduct, progress is blocked by the gate that was lowered when first entering The Fractured Drain. This happens even on repeated entry/exit from The Fractured Drain. Progress requires a fast travel to another area and back to The Barren Aqueduct.
Thanks - I had misunderstood your post on first reading, since I was (incorrectly) thinking that it was a clickable/interactable thing, rather than destructible environment.