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