Some lock flights have pumps to keep the ponds at the top full of water because they are near the highest point in the area so they can't refill naturally fast

Some lock flights have pumps to keep the ponds at the top full of water because they are near the highest point in the area so they can't refill naturally fast enough or simply to avoid depleting the upstream water source. See, e.g., https://en.wikipedia.org/wiki/Caen_Hill_Locks https://en.wikipedia.org/wiki/Caen_Hill_Locks