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<br />e <br /> <br />Head-cutting - Channel bottom erosion moving upstream through a basin indicating that <br />a readjustment of the basin's slope and its stream discharge and sediment <br />load characteristics is taking place. Head-cutting often leaves streambeds in <br />an unstable condition as it progresses through a reach. <br /> <br />Helical flow - Three-dimensional movement of water particles along a spiral path in the <br />general direction of flow. These secondary-type currents are of most <br />significance as flow passes through a bend; their net effect is to remove soil <br />particles from the cut bank and deposit this material on the point bar. <br /> <br />Hydraulic radius - Equal to AlP, where A is cross-sectional area and P is wetted <br />perimeter. Roughly comparable to depth in wide, shallow streams. <br /> <br />Impenneable material - A soil that has properties which slow down movement of water <br />through the material. <br /> <br />Infiltration - That portion of rainfall or surface runoff that moves downward into the <br />subsurface rock and soil. <br /> <br />Intermittent stream - A stream that flows most of the time, but ceases to flow seasonally <br />or occasionally because bed seepage and evaporation exceed the supply of <br />water. <br /> <br />Invert - The minimum bed elevation of a channel or culvert. <br /> <br />Iowa vanes (also referred to as Odgaard vanes) - Baffle type structures placed in series <br />along the outsides of meander bends to prevent erosion by disrupting <br />secondary currents. <br /> <br />Launching - Release of unden:ut material (stone riprap, rubble, slag. etc.) downslope; if <br />sufficient material accumulates on the streambank face, the slope can <br />become effectively annored. <br /> <br />Levee - An embankment landward of top bank that confines flow during highwater <br />periods, thus preventing overflow into lowlands. <br /> <br />Live cribwaIl- A cribwaII constructed of timbers or logs through which the growing tips <br />of live brush projecL The interior of the structure consists of alternating <br />layers of soil and brush. <br /> <br />Live stakes - Stakes 2 to 3 feet long cut from live donnant brush and driven into the <br />ground to sprouL <br /> <br />Lower bank . That portion of a streambank having an elevation less than the mean water <br />level of the stream. <br /> <br />Macroinvertebrates - Large invertebrates found in streams and consisting primarily of <br />larval insects, worms. and related organisms. <br /> <br />e <br /> <br />Colorado Erosion Control Manual <br /> <br />XIX <br />