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<br />Depth of Scour - The vertical distance a streambed is lowered by scour below a <br />reference elevation. <br /> <br />Dike - An impermeable linear structure for the control or containment of <br />overbank flow; a dike trending parallel with a river bank differs from a levee only in <br />that the dike extends for a much shorter distance along the bank. <br /> <br />Dike (qroin. spur. ietty) - A structure extending from a bank into a channel that <br />is designed to: (a) reduce the stream velocity as the current passes through the <br />dike, thus encouraging sediment deposition along the bank (permeable dike); or (b) <br />deflect erosive currents away from the streambank (impermeable dike). <br /> <br />Discharqe - Volume of water passing through a channel during a given time. <br /> <br />Dominant Discharqe - The formative discharge in a specific channel for a <br />specific channel feature. The dominant discharge for hydraulic geometry <br />relationships is assumed to be the bankfull discharge and it is assumed that the <br />bankfull discharge has a return period of approximately I. ') years. <br /> <br />Drift - Alternative term for "debris." <br /> <br />Drainaqe Basin - An area confined by drainage divides, often hav ing only one <br />outlet for discharge. <br /> <br />Eddy Current - A vortex -type motion of a fluid flowing cont.rary to the main <br />current, such as the circular water movement that occurs when the main flow <br />becomes separated from the bank. <br /> <br />Embankment End Slope - Conical slope at end of road approach embankment. <br /> <br />Enerqy Grade Slope - An inclined line representing the total energy of a stream <br />flowing from a higher to a lower elevat.ion. For open-channel flow the energy grade <br /> <br />slope is located a distance of V2/2g apove the water surface (V ~ velocity and g = <br />acceleration due to gravity). <br /> <br />Entrenched Stream - Stream cut into bedrock or consolidated deposits. <br /> <br />Environmental - Pertaining to t.he effects of engineering works on their <br />surroundings and on nature. <br /> <br />Ephemeral Stream - A stream or reach of a stream that does not flow For parts <br />of the year. As used here, the term includes intermittent streams whose flow is less <br />than perennial but more then ephemeral. <br /> <br />~rosion - Displacement of soil particles on the land surface due to water or <br />wind action. <br /> <br />Erosion Control Matting - Fibrous matting (e.g. jute, paper, etc.) placed or <br />sprayed on a streambank fur the purpose of preventing erosion or providing <br />temporary stabili.lation until vegetation is established. <br /> <br />xliv <br /> <br />I <br />.J <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />-- <br />I <br />I <br />I <br />I <br />I <br />I <br />J <br />I <br />. <br />