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<br />---- <br /> <br />----. <br /> <br />Head-c:.uing - Channel bottom emsion moving upstream through a basin indicating that <br />a readjustment of the basin's slope and its stream discharge and sediment <br />load characterislics is laking place. Head-cUlling often leaves streambeds in <br />an unstable condition lIIS it progresses through a reach. <br /> <br />Helicalllow - Three-dimensional movement of water partides along a spiral path in the <br />general direction of flow. 'Ibese secondary-type currents are of most <br />significance as flow passes through a bend; their net effecl is to remove soil <br />particles from tile cut bank and deposit this mallOrial on the point bar. <br /> <br />Hydraulic radius - Equal to NP, whe~e A is cross-sectional Well and P is welled <br />perimeter. Roughly comparable to depth in wide, shallow streams. <br /> <br />Impermeable material - A soillthat has properties which slow down movement of water <br />through the material. <br /> <br />Infiltration - That portion of rainfall or :;urface runoff that moves downward into the <br />subsurface rock and soil. <br /> <br />Intennitltent stream - A stream that flows most of the time, but CeaS<$ 1:0 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 cwrents. <br /> <br />Launchil~g - Release of W1den:ut material (stone riprap, rubble, slag, etc.) downslope; if <br />sufficient material acc:umulales on the stream bank face, the slope can <br />become effectiVl,ly annored, <br /> <br />Levee - An embankment landward of top bank that conlines flow during high water <br />periods, thus preventing overflow into lowlands. <br /> <br />Live cribwall - A cribwall construc:ted of limbers or logs througb wbich Ihe growing tips <br />of live brush project. The interior of the structure consisL~ of alternating <br />layers of soil and brush. <br /> <br />Live stakes - Stakes 2 to 3 ff:et long cut from live donnant brush and driven into the <br />ground to sprout. <br /> <br />Lower bank - That portion of a stnoambank having an elevation less than the mean water <br />level of the stream. <br /> <br />Macroinvertebrates - Large invertebrates found in streams and consi~ting primarily of <br />larval insects, wonns, and related organisms. <br /> <br />Colorado Erosion Control Manual <br /> <br />XIX <br />