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