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<br />confluence: <br /> <br />The junction of two or more streams, <br /> <br />constriction: <br /> <br />A natural or artificial control section, such as a bridge crossing, channel <br />reach or dam, with limited flow capacity in wbich the upstream water <br />surface elevation is related to discharge: <br /> <br />contact load: <br /> <br />Sediment particles that roll or slide along in almost continuous contact <br />with the streambed, <br /> <br />contraction: <br /> <br />The effect of channel or bridge constriction on flow streamlines. <br /> <br />countermeasure: <br /> <br />A measure intended to prevent, delay or reduce the severity of hydraulic <br />problems. <br /> <br />contraction scour: <br /> <br />Scour in a channel or on a floodplain that is not localized at a pier, <br />abutment, or other obstruction to flow. In a channel, contraction scour <br />results from the contraction of streamlines and usually affects all or most <br />of the channel width. <br /> <br />crib: <br /> <br />A frame structure filled with earth or stone ballast, designed to reduce <br />energy and to deflect streamflow away from a bank or embankment. <br /> <br />critical shear stress: <br /> <br />The minimum amount of shear stress required to initiate soil particle <br />motion, <br /> <br />crossing: <br /> <br />The relatively short and shallow reach of a stream between bends; also <br />crossover. <br /> <br />cross section: <br /> <br />A section nonna! to the trend of a channel or flow, <br /> <br />current: <br /> <br />Water flowing through a channel. <br /> <br />cut bank: <br /> <br />The concave wall of a meandering stream, <br /> <br />cutoff: <br /> <br />(a) A direct channel, either natural or artificial, connecting two points on <br />a stream, thereby shortening the original length of the channel and <br />increasing its slope; (b) A natural or artificial channel which develops <br />across the neck of a meander loop, <br /> <br />cutoff wall: <br /> <br />A wall, usually of sheetpiling or concrete, that extends down to <br />scour-resistant material or below the expected scour depth, <br /> <br />daily discharge: <br /> <br />Discharge averaged over one day, <br /> <br />debris: <br /> <br />Floating or submerged material, such as logs or trash, transported hy a <br />stream. <br /> <br />degradation (bed): <br /> <br />A general and progressive lowering of the channel bed due to scour. <br /> <br />density of water-sediment <br />mixture: <br /> <br />Bulk density (mass per unit volume) including both water and sediment. <br /> <br />depth of scour: <br /> <br />The vertical distance a streambed is lowered by scour below a reference <br />elevation, <br /> <br />xvi <br />