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<br />River Mec:henlcs end Geomorphology <br /> <br />- <br /> <br />2.3.2 Controlling Variables. <br /> <br />Fluvial vilriables included in this discussion are the fluid properties, sediment <br />properties, channel shape. and the flow characteristics. Alluvial system variables may be <br />classified as either independent or dependent 1bose which are imposed upon the river <br />and over which the river has no control are the independent variables. Care must be <br />taken in distinguishing which time cycle a given variable is being classified under. For <br />example,n the short tenn (steady time), sediment is a dependent variable expressed as <br />a functior of velocity; whereas in the long tenn (graded-time), both are independent <br />variables and the river adjusts to sediment inflow from upper reaches. Table 2-1 <br />summariz,:g river variables and their status as independent or dependent variables for <br />the designated time cycles. (Chang, 88) <br /> <br />TABLE 2 - 1 <br /> <br />Variable volue based on time (Reprinted from Schumm, 1971) <br /> <br />Veri_.. <br />Geology <br />Palceoclim'le <br />Valley Slole, width & depth <br />Climate <br />Vegetation (type and density) <br />Mean wale r discharge <br />Mean sediment inflow rate <br />Channel mo)[phology <br />Observed Cischarge and load <br />Hydraulics of flow <br /> <br />StoHy (ShorN.....) <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />D <br />D <br /> <br />Gnlded (Long......) Geologic (Vory long) <br />I I <br />I I <br />I D <br />I X <br />I X <br />I X <br />I X <br />D X <br />X X <br />X X <br /> <br />I, Independent variable; D. Dependent variable; X, Indelenninate <br /> <br />2.3.3 Sedimentation. <br /> <br />Sediment~ion embodies the processes of erosion, entrainment, transportation, <br />depositiorl, and compaction of sediments. Fluvial channels, by definition, are primarily <br />a function of these complex and not wholly understood processes. This section presents <br />some gemral considerations relative to the transport of sediment within a river reach. <br />ASCE Mmual 54 "Sedimentation Engineering" (1975) provides a detailed treatise on <br />all aspecll: of sedimentation. <br /> <br />The amoLDt of material transported or deposited in a river reach under a given set of <br />conditiom: is the result of the interaction of two groups of variables. In the first group <br />are those which influence the quantity and quality of the sediment supply to the reach. <br />In the second group are the variables which influence the sediment lransport capacity of <br />the stream. It is extremely important to recognize that one of these will be the <br />controllin g condition which dictates the stream response. <br /> <br />. <br /> <br />8 <br /> <br />Colorado) Erosion Control Manual <br />