U.S. Fish & Wildlife Service Low Hazard Dams - Association of State ...

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U.S. Fish & Wildlife Service Low Hazard Dams - Association of State ...

STANDING OPERATING PROCEDURESAPPENDIX AGLOSSARYAbutment. The undisturbed natural material of the valley side against which the dam isconstructed. The left and right abutments are defined as being on the right and left side of anobserver looking downstream.Acre-Foot. A term used in measuring the volume of water that would cover one acre to a depthof one foot. It is equal to 43,560 cubic feet.Air-Vent Pipe. A pipe designed to provide air to the outlet conduit to reduce turbulence duringrelease of water. Extra air is usually necessary downstream on constrictions.Appurtenant Structure. A structure necessary for the operation of a dam such as outlets,trashracks, valves, spillways, power plants, tunnels, etc.Arch Dam. A concrete or masonry dam that is curved so as to transmit the major part of thewater pressure to the abutments.Auxiliary Spillway. See SpillwayBase Width (Base Thickness). The maximum width or thickness of a dam measured horizontallybetween upstream and downstream faces and normal (perpendicular) to the axis of the dam butexcluding projections for outlets, etc.Berm. A horizontal step or bench in the sloping profile of an embankment dam.Breach. An eroded opening through a dam that drains the reservoir. A controlled breach is aconstructed opening. An uncontrolled breach is an unintentional opening that allowsuncontrolled discharge from the reservoir.Butress Dam. A dam consisting of a watertight upstream face supported at intervals on thedownstream side by a series of buttresses.Channel. A general term for any natural or artificial watercourse.Cofferdam. A temporary structure enclosing all or part of a construction area so thatconstruction can proceed in a dry area. A diversion cofferdam diverts a river into a pipe,channel, or tunnel.Conduit. A closed channel to convey water through, around, or under a dam.A-1Revision No. 0October 2008

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