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<br />Concrete block - Precast concrete material placed on a streambank or <br />fi Iter to prevent erosion. <br /> <br />Confluence - The junction of two or more streams. <br /> <br />Constriction (flow) - A reduction in channel cross-sectional area that <br />results in greater stream velocities and/or water depth. <br /> <br />Crib - A frame structure, fi I led with earth or stone bal last, designed <br />to abaorb energy and to deflect streamflow away from a bank. <br /> <br />Critical shear stress - The minimum amount of shear stress exerted by <br />passing stream currents required to initiate soi I particle <br />motion. <br /> <br />Cross section - A diagram or drawing cut across a channel that <br />illustrates the banks, bed, and water surface. <br /> <br />Crossing - The relatively short and shal low reach of a stream between <br />bends; also called a crossover. <br /> <br />Current - water flowing through a channel. <br /> <br /> <br />Cut bank - The concave wal I of a meandering stream. <br /> <br />Cui:off - A new, relatively short channel (natural or artificial) <br />formed when a stream cuts or is real igned through the neck of an <br />oxbow or horseshoe bend. A cutoff can also develop as successive <br />high-water flows develop a chute across the inside of a point <br />bar. <br /> <br />Degradation (bed) - A progressive lowering of the channel bed due to <br />scour. Degradation is an indicator that a change in the stream's <br />discharge and sediment load characteristics is taking place. <br /> <br />Dike (groin, spur, jetty) - A structure extending from a bank into a <br />channel that is designed to (a) reduce the stream velocity as the <br />current passes through the dike, thus encouraging sediment <br />deposition along the bank (permeable dike) or (b) deflect erosive <br />currents away from the streambank (impermeable dike). <br /> <br />Discharge - Volume of water passing through a channel during a given <br />time, usually measured in cubic feet per second. <br /> <br />Drainage basin - An area confined by drainage divides, often having <br />only one outlet for discharge. <br /> <br />Eddy current - A vortex-type motion of a fluid flowing contrary to the <br />main current, such as the circular water movement that occurs <br />when the main flow becomes separated for the bank. <br /> <br /> <br />Energy grade slope - An incl ined representing the total energy of a <br />stream flowing from a higher to a lower elevation. <br /> <br />75 <br />