habitat — Ttie place where a population of animals lives and its sur- 

 roundings, both living and nonliving; includes the provision of life 

 requirements such as food and shelter. 



high-water channel — A channel that is dry most of the ice-free season, 

 but contains flowing water during floods. 



hydraulics — The science dealing with the mechanical properties of fluids 

 and their application to engineering; river hydraulics deals with 

 mechanics of the conveyance of water in a natural watercourse. 



hydraulic depth — The average depth of water in a stream channel. It is 

 equal to the cross-sectional area divided by the surface width. 



hydraulic geometry — Those measures of channel configuration, including 

 depth, width, velocity, discharge, slope, and others. 



hydraulic radius — The cross-sectional area of a stream of water divided 



by the length of that part of its periphery in contact with its contain- 

 ing channel; the ratio of area to wetted perimeter. 



hydrograph — A graph showing, for a given point on a stream, the discharge, 

 stage, velocity, or another property of water with respect to time. 



hydrology — The study of the origin, distribution, and properties of water 

 on or near the surface of the earth. 



ice-rich material — Permafrost material with a high water content in the 



form of ice, often taking the shape of a vertical wedge or a horizontal 

 I ens. 



impervious — A term applied to a material through which water cannot pass 

 or through which water passes with great difficulty. 



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