Controllably, the chamber may be filled either with air from an external source of {HEAD ~ pressurized air} or may be allowed to flood through the channel with {TAIL ~ water} from the surrounding body of water 
Controllably , the chamber may be filled either with air from an external source of { HEAD ~ pressurized air } or may be allowed to flood through the channel with { TAIL ~ water } from the surrounding body of water
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH