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OG}8J~ by the fluid motion are termed "suspended load." Materials moving along the bed that are panially supponed by intermittently resting upon one another are referred to as "bedload." Depending on the panicle sizes available, the sediment may be transponed as suspended or bedload. Water and sediment in a natural channel are ultimately derived from the drainage basin. The enormous variability of rock materials, topography and biota found in nature combined with the variety of climates prevailing over the globe, result in the myriad combinations of materials and settings which characterize the environments of natural alluvial channels. The result is great variation in the flows and imposed sediment to which rivers are subjected. Panicle sizes found on the bed and banks of river channels reflect the composition and character of the geology and topography of source areas and the ability of flows to move the materials. The presence of vegetation, again of potentially great diversity such as grasses, shrubs, or trees, may affect flow in the channel as well as influencing the composition, structure and resistance to erosion of both bed and banks. Thus, variability both at a regional scale and at a place characterizes the size and shape of alluvial river channels. While there is much variability across the entire spectrum of alluvial channels, distinctive broad regional similarities characterize different kinds of rivers. Among alluvial rivers, gravel- bed and sand-bed rivers have been differentiated (Simons and Simons, 1987). Gravel-bed alluvial rivers are those whose beds are primarily composed of unconsolidated material with median sizes larger than sand that is, greater than 2mm. Gravel-bed channels are characteristic of the Upper Snake River system. In many such channels, both bed and banks are dominated by gravels. Gravel-bed rivers typically have a pavement or armor layer of coarser materials covering the bed channel. Although suspended sediment usually constitutes more of the total sediment load than bedload, it plays a less important role in determining channel morphology (Leopold, \ 992). Suspended load may be important in forming the channel in finer grained systems and, even in gravel-bed rivers, suspended load may playa role in floodplain and bank formation. In general, smaller panicles (suspended sediment) are moved by all flows, while larger flows are needed to move the larger particles making up the channel bed. Consequently, as bed- material size increases, the discharge required to cause changes in channel morphology increases. Much of the bedload in gravel-bed channels is composed of sand and fine gravel panicles. This sediment is mobile over a large range of flows and is often supply limited, that is, the stream has more energy than is needed to move the available material. The coarse sediment, which makes up much of the bed, and which is mobile only during higher flows, may be transpon limited, that is, the supply is not limited but movement is controlled by the energy of the streamflow. Characterizing the transport of both the finer and coarser fractions of the bed materials, Emmett (1976) suggested the existence of two distinct phases of bedload transpon in armored channels: a fIrst phase in which finer sediment moves over the coarser substrate, and a second phase in which the coarser channel-forming materials become mobile (Jackson and Beschta, 1982; Beschta, 1987; Ashworth and Ferguson, 1989; Warbunon, 1992). United Slates' Expert Report Disclosing Mell1odologies for Quantification of Organic Ad Claims Consolidated Subcase No, 63-25243 II