NPDP Dam Dictionary

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Term AKA Definition
Backfill Material used in refilling excavation, or the process of such refilling.
Backfill concrete Concrete used in refilling excavation in lieu of earth material.
Backwater A small, generally shallow body of water attached to the main canal, with little or no current of its own. Stagnant water in a small stream or inlet. Water moved backward or held back by a dam, tide, etc.
Baffle block One of a series of upright obstructions designed to dissipate energy as in the case of a stilling basin or drop structure (also referred to as dentate).
Balanced head condition The condition in which the water pressure on the upstream and downstream sides of an object are equal (such as a emergency or regulating gate).
Ball-milling The repeated churning action of cobbles, gravel, and sand caused by the force of water in a stilling basin or other structure by which severe concrete abrasion can occur.
Bank storage Water that has inflitrated from a reservoir into the surrounding land where it remains in storage until water level in the reservoir is lowered.
Barrage Gate-structure dam A barrier built across a river, comprising a series of gates which when fully open allow the flood to pass without appreciably increasing the flood level upstream of the barrage.
Base flow Groundwater inflow to the river. Portion of stream discharge that is derived from natural storage.
Base width or thickness The maximum thickness or width of the dam measured horizontally between upstream and downstream faces and normal to the axis or centerline crest of the dam, but excluding projections for outlets, etc. In general, the term thickness is used for gravity or arch dams, and width is used for other dams.
Baseload plant Powerplant normally operated to carry baseload; consequently, it operates essentially at a constant load.
Baseloading Running water through a powerplant at a roughly steady rate, thereby producing power at a steady rate.
Batter Inclination from the vertical. A pile driven at an angle to widen the area of support and to resist thrust.
Beaching The action of water waves by which beach materials settle into the water because of removal of finer materials.
Bed material Unconsolidated material of which a streambed is composed.
Bedding Ground, or layer of such, for support purposes on which pipe is laid. Soil placed beneath and beside a pipe to support the load on the pipe.
Bedding plane A separation or weakness between two layers of rock, caused by changes during the building up of the rock-forming material.
Bedload Coarse sediments carried along near the bottom of a river.
Bedrock The solid rock at the surface or underlying other surface materials. Rock of relatively great thickness and extent in its native location. A general term for any solid rock, not exhibiting soil-like properties, that underlies soil or other unconsolidated surficial materials. As distinguished from boulders.
Bell An expanded end of a pipe section, into which the next pipe fits.
Bench A working level or step in a cut.
Bench mark BM A permanent or temporary monument of known elevation above sea level, used for vertical control at a construction site. A point of known or assumed elevation used as a reference in determining other elevations.
Berm A horizontal strip or shelf built into an embankment or cut to break the continuity of the slope, usually for the purpose of reducing erosion or to increase the thickness of the embankment at a point of change in slope or defined water surface elevation. A horizontal step in the sloping profile of an embankment dam. A shelf that breaks the continuity of a slope, or artificial ridge of earth. A ledge or shoulder, as along the edge of a road or canal. An artificial ridge of earth.
Bituminous Containing asphalt or tar.
Boring Rotary drilling.
Borrow Material excavated from one area to be used as fill material in another area.
Borrow areas Generally, surface areas, that contain borrow pits. The area from which material for an embankment is excavated.
Borrow pits Specific site(s) within a borrow area from which material is excavated for use.
Boulder A rock fragment, usually rounded by weathering or abrasion, with an average dimension of 12 inches or more: will not pass a 12-inch screen. A rock which is too heavy to be lifted readily by hand.
British thermal units BTU Quantity of heat required to raise the temperature of one avoirdupois pound of water 1øF at or near 39.2øF.