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<br />I <br />Ie <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 />il <br /> <br />GLOSSARY <br /> <br />A listing of terms related to highways and river environment, streambank <br />protection, and river mechanics is provided below: <br /> <br />Abrasion - Removal of streambank material due to entrained sediment, ice, or <br />debris rubbing against the hank. <br /> <br />l\ fflux - Backwater or height by which water levels are raised at a stated point, <br />owing to presence of a constriction or obstruction, such as a bridge. <br /> <br />l\...99!'adation (bed) - A progressive buildup or raisinlj of the channel bed due to <br />sediment deposition. Permanent or continuous aggradation is an indicator that a <br />change in the stream's discharge and sediment load characteristics is taking place. <br /> <br />Alluvium - Unconsolidated material deposited by a stream in a channel, <br />floodplain, alluvial fan, or delta. <br /> <br />Alluvial Channel - Channel wholly in alluvium; no bedrock is exposed in channel <br />at low flow or likely to be exposed by erosion. A channel whose processes are <br />controlled by the flow and boundary interactions. <br /> <br />l\lluvial Fan - A landform shaped like a fan in plan view and deposited where a <br />stream issues from a narrow valley of high slope onto a plain or broad valley of low <br />slope. <br /> <br />Anabranch - Individual channel of an anabranched stream. <br /> <br />l\nabranched Stream- A stream whose flow is divided at normal and lower <br />stages by large islands or, more rarely, by large bars; the width of individual islands <br />or bars is greater than about three times the water \yidth; the channels are more <br />widely and distinctly separated than those of a braided stream. <br /> <br />l\nqle of Repose - The maximum angle (as measured from the horizontal) at <br />which gravel or sand particles can stand. <br /> <br />l\nnual Flood - The maximum flow in one year (may be daily or instantaneous). <br /> <br />~pron - Protective material laid on a streambed to prevent scour. <br /> <br />Apron. Launchinq - An apron designed to settle and protect the side slopes of a <br />scour hole after settlement. <br /> <br />l\rmor - Surfacing of channel bed, banks, or embankment slope to resist erosion. <br /> <br />Armorinq - (a) Natural process whereby an erosion-resistant layer of relatively <br />large particles is formed on a streambank due to the removal of finer particles by <br />streamflow. (b) Placement of a covering on a streambank to prevent erosion. <br /> <br />Articulated Concrete Mattress - Rigid concrete slabs, which can move as scour <br />occurs without separating, usually hinged together with corrosion-resistant wire <br />fasteners; primarily placed for lower bank protection. <br /> <br />xxxix <br />