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<br />GLOSSARY OF TERMS FOR DAM SAFETY <br /> <br />Abutment. That part of the valley side against which the dam is constructed. <br />An artificial abutment is sometimes constructed, as a concrete gravity sec- <br />tion, to take the thrust' of an arch dam where there is no suitable natural <br />abutment. The left and right abutments of dams are defined with the observer <br />viewing the dam looking in the downstream direction, unless otherwise <br />indicated. <br /> <br />Acre-foot. A unit of volumetric measure that would cover one acre to a depth <br />of one foot. It is e~ual to 43,560 cubic feet. <br /> <br />Adit. A nearly horizontal underground excavation in an abutment having an <br />opening in only one end. An opening in the face of a dam for access to <br />galleries or operating chambers. <br /> <br />Appurtenant structure. Ancillary features of a dam such as outlets, <br />spillways, powerplants, tunnels, etc. <br /> <br />Axis of dam. The vertical plane or curved surface, chosen by a designer, <br />appearing as a line, in plan or in cross-section, to which the horizontal <br />dimensions of the dam are referenced. <br /> <br />Baffle block. A block, usually of concrete, constructed in a channel or <br />stilling basin to dissipate the energy of water flowing at high velocity. <br /> <br />Base thickness. Also referred to as base width. The maximum thickness or <br />width of the dam measured horizontally between upstream and downstream faces <br />and normal to the axis of the dam, but excluding projections for outlets, or <br />other appurtenant structures. <br /> <br />Bedrock. The consolidated body of natural solid mineral matter which <br />, underlies the overburden soils. <br /> <br />Berm. A nearly horizontal step in the sloping profile of an embankment dam. <br />Also a step in a rock or earth cut. <br /> <br />Borrow area. The area from which material for an embankment is excavated. <br /> <br />Breach. An eroded opening through a dam which drains the reservoir. A con- <br />trolled breach is a constructed opening. An uncontrolled breach is an <br />unintentional opening which allows uncontrolled discharge from the reservoir. <br /> <br />Channel. A general term for any natural or artificial facility for conveying <br />water. <br /> <br />Compaction. Mechanical action which increases the density by reducing the <br />voids in a material. <br /> <br />-1- <br />