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<br />0018J8 <br /> <br />channels have a cross-sectional area, width. and depth at bankfull discharge' that is related to the <br />range of flows capable of eroding and transponing the alluvial deposits constituting the channel <br />boundaries. <br /> <br />A variety of terms have been used to characterize rivers (and canals) flowing in alluvium <br />(river deposited material) encompassing the concepts of adjustability and the tendency of a <br />channel to develop a size and shape reflecting the range of flows and the quantity and <br />characteristics of the sediment to which the channel is subjected. Among the commonly used <br />terms are equilibrium, quasi-equilibrium, steady state, regime (Blench, 1966; Richards, 1982; <br />Langbein and Leopold, 1964) and grade (Mackin, 1948, pp. 471-484). All embody the concept <br />enunciated by Mackin in his classic paper on the graded river that: "A graded stream is one in <br />which, over a period of years, slope is delicately adjusted to provide, with available discharge, <br />just the velocity required for the transponation ofload supplied from the drainage basin." <br /> <br />While erosion and deposition may take place, the channel neither aggrades (raises) or <br />degrades (lowers) its mean bed over a period of time. The word "grade" which initially referred <br />to gradient, as in railroad grade, has taken on the broader concept of equilibrium involving <br />channel characteristics as well as slope. Additionally, it is now recognized that stream power or <br />shear stress, not velocity, is responsible for sediment transpon. The time scale is important <br />because channel behavior may vary over different time scales, and over very long periods of <br />geologic time, stable equilibrium is not maintained as the landscape is denuded or reduced in <br />elevation. Similarly, marked changes in climate, as in periods of glaciation for example, may <br />alter the hydrologic regimen of the drainage basin, thus altering the temporal and spatial <br />distribution of streamflow and sediment movement. <br /> <br />2. Channel Processes <br /> <br />In an open channel in which both the bed and banks are fixed boundaries, and no <br />sediment is being transported, the depth and velocity of the flow and the profile of the water <br />surface for a given discharge, are controlled by the gradient or slope of the channel, the <br />resistance to flow impaned by the boundary materials and the channel size and shape. In <br />contrast, in a channel with mobile boundaries where the flow may alter both the form of the bed <br />as well as the position of the bed and banks through erosion and deposition, channel size and <br />shape reflect a dynamic interaction of erosion, transport and deposition. At low flow little or no <br />sediment may be in motion. As flow increases, smaller panicles may be entrained with <br />progressively larger particles in motion at successively higher flows. With increasing flow, the <br />energy available to transport sediment generally increases, as reflected in the distributions of <br />depth, velocity, and slope (longitudinal gradient). Solid panicles which are held in suspension <br /> <br />'Bankfull discharge refers to the discharge (volume of streamflow per unit time) corresponding to bankfull <br />stage. Bankfull stage refers to the water level (stage) corresponding to the top of the channel banks <br />which also corresponds to the level of the floodplain. <br /> <br />United States' Expert Report Disclosing Melhodologies for Quantifica1ion of Organic Ar1. Claims Corsoiidated Subcase No, 63-25243 <br /> <br />10 <br />