Looking SE from air toward Lock and Dam No. 41 (later McAlpine Locks and Dam), Portland Canal and Falls of the Ohio
Beartraps (apparently so-named because of a superficial resemblance to an archaic type of animal trap) are movable dams which, when lowered, allow water and floating debris to flow over them.
They would have helped prevent debris from piling up against the upstream face of the hydroelectric plant.