cover, instream — Areas of shelter in a stream channel that provide aquatic 

 organisms protection from predators or a place in which to rest, or 

 both, and conserve energy due to a reduction in the force of the cur- 

 rent . 



cross section area — The area of a stream, channel, or waterway opening, 

 usually taken perpendicular to the stream center line. 



current — The flowing of water, or other fluid. That portion of a stream 



of water which is moving with a velocity much greater than the average 

 or in which the progress of the water is principally concentrated (not 

 to be confused with a unit of measure, see velocity). 



datum — Any numerical or geometrical quantity or set of such quantities 



which may serve as a reference or base for other quantities. An agreed 

 standard point or plane of stated elevation, noted by permanent bench 

 marks on some solid immovable structure, from which elevations are meas- 

 ured, or to which they are referred. 



dewater — The draining or removal of water from an enclosure or channel. 



discharge — The rate of flow, or volume of water flowing in a given stream 

 at a given place and within a given period of time, expressed as cu 

 ft per sec. 



drainage area — The entire area drained by a river or system of connecting 

 streams such that all stream flow originating in the area is discharged 

 through a single outlet. 



dredge — Any method of removing gravel from active channels. 



drift, invertebrate — The aquatic or terrestrial invertebrates which have 

 been released from (behavioral drift), or have been swept from (catas- 

 trophic drift) the substrate, or have fallen into the stream and move 

 or float with the current. 



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