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<br />OJ18J~ <br /> <br />transponed (effective discharge) and the bankfull flow. Several investigators (Wolman and <br />Miller, 1960; Andrews, 1980) have suggested that effective discharge increases as the discharge <br />threshold necessary to induce movement of sediment increases. <br /> <br />Because many correlations have been demonstrated between discharge at the bankfull <br />stage and channel features such as area of cross-section, width, and depth, this discharge is <br />sometimes referred to as the "channel forming" or "dominant discharge." The process of <br />channel formation, in natural channels through erosion and deposition, however, customarily <br />involves a range of flows for which a single value, such as the dominant discharge, is a <br />surrogate. Such surrogates are commonly employed in stream restoration projects under the <br />assumption that the surrogate discharge in fact reflects or captures the range of flows responsible <br />for the channel form (Hey, 1986; Rosgen, 1996). <br /> <br />The pattern or planform of the river may also vary. Thus, rivers are often characterized <br />as straight, meandering, or braided, the last representing streams containing islands around which <br />the flow moves in threads (Leopold et ai,. 1964). More elaborate classifications make finer <br />distinctions in degrees of sinuosity of the thread of the channel and in apparent relationships <br />between the panicle sizes in transport and depositional patterns (Church, 1994; Bray and <br />Kellerhals, 1979). <br /> <br />In addition to changes in cross-sectional form and pattern, alluvial channels are not fixed <br />in place but through erosion and deposition may move across the valley bottom. Rates of <br />movement are highly variable depending upon the erodibility of the bank materials and the flow <br />characterizing the hydrologic regimen. Rates of lateral migration of some meanders include high <br />values such as one channel width in several years or less than a decade, while elsewhere a <br />channel may remain fixed in place for decades (Hooke, 1980). <br /> <br />Because rivers occur in diverse climatic, hydrologic and geologic environments <br />throughout the world, there is enormous variety in the mix of flow characteristics and <br />sedimentary materials encountered in river systems. At the same time, in a given region or <br />setting, the river system may demonstrate a characteristic assemblage of forms resulting from a <br />panicular hydrologic regimen and geologic setting. The river channels included in the channel <br />maintenance claims in the Snake River Basin Adjudication are self-formed adjustable channels <br />within the commonly accepted definitions of these terms in the geomorphological and <br />engineering literature cited above. The specific nature of the controls of water and sediment to <br />which these channels respond are described in subsequent sections of this Repon. <br /> <br />United States' Expert Report Dlsdosing Me1!lodologies for Quanlificallon of Organic Ad Claims ConsoIidatad Subcase No, 63-25243 <br /> <br />14 <br />