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<br />Incised Reach - The stretch of river with a incised channel that only rarely <br />overflows its banks. <br /> <br />Incised Stream - A stream that flows in an incised channel with high banks. <br />Banks that stand more than 15 ft above the water surface at normal stage are <br />regarded as high. <br /> <br />Instantaneous Discharqe - A discharge at a given moment. <br /> <br />Invert - 1 he lowest point in the channel cross section or at flow control devices <br />such as weirs, culverts, or dams. <br /> <br />Island - A permanently vegetated area, emergent at normal stage, that divides <br />the flow of a stream. Some islands originate by establishment of vegetation on a <br />bar, and other originate by channel avulsion or at the junction of minor tributaries <br />with a stream. <br /> <br />Jack - A device for flow control and protection of banks against lateral <br />erosion; it has six mutually perpendicular arms rigidly fixed at the center. Steel <br />jacks are strung with wire; Kellner jacks are made of three steel struts; concrete <br />jacks are made of three reinforced concrete beams bolted together..at the midpoints. <br /> <br />Jack Field - Rows of jacks tied together with cables, some rows generally <br />parallel with the banks and some perpendicular thereto or at an angle. Jack fields <br />may be placed outside or within a channel. <br /> <br />,;I etty - An alternative term for a 'spur.' <br /> <br />Lateral Erosion - Erosion in which the removal of material has a dominately <br />lateral component, as contrasted with scour in which the component is dominately <br />vertical. <br /> <br />!"aunchinq - Release of undercut material (stone riprap, rubble, slag, etc.) <br />downslope; if sufficient material accumulates on the streambank face, the slope can <br />become effectively armored. <br /> <br />Leve~ - An embankment generally landward of top bank that confines flow <br />during high water periods, thus preventing overflow into lowlands. <br /> <br />Littoral Drift - The transport of material along a shoreline (also 'long-shore <br />sediment transport'). <br /> <br />Local Scour - Scour in a channel or on a flood plain that is localized at a pier, <br />abutment, or other obstruction to flow. <br /> <br />Load (or sediment load) - Amount of sediment being moved by a stream. <br /> <br />Lonqitudinal Profile - 1 he profile of a stream or channel drawn along the length <br />of its centerline. In drawing the profile, elevations of the water surface or the <br />thalweg are plotted against distance as measured from the mouth or from an <br />arbitrary initial point. <br /> <br />xlviii <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 />I <br />-I <br />I <br />