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LITERATURE REVIEW ' Sand-bedded rivers have been the focus of much study, often because of their impact on humans. Early engineering studies focused on reducing the impacts of flooding and migrating ' rivers on human structures, but more recently geomorphologists have endeavored to improve the understanding of why and how rivers fonn, migrate, and change. Only recently have geomorphologists combined their efforts with biologists and ecologists to discern the effects of ' physical attributes and changes in those attributes on the ecology of river systems. Geomorphology of Sand-Bedded Rivers 1 Self-Formed Channels Continually adjusting streams that flow within banks composed of material previously transported by the river are termed self-formed channels and are the focus oflong-standing geomorphic research. The Green River within the alluvial Ouray NWR reach is an example of a self-formed channel. For self-formed channels, the channel form at a given cross section is determined by discharge, quantity and character of the sediment in transport, and bank and bed characteristics [Leopold et al., 1964]. Consequently, in channels with a moveable bed and banks, channel form results from the dynamic interaction of bank stability, flow, and sediment transport [Leopold et al., 1964]. This relationship is dynamic because in natural rivers neither bank and bed material nor flow conditions are uniform in space or time. Classic geomorphic research on self-formed streams such as Watts Branch (Maryland), Brandywine Creek (Pennsylvania), and Baldwin Creek (Wyoming) measured characteristic parameters of streams such as the spacing of pools and riffles, distribution of sediment sizes on the bed, bedload movement, channel shape through meanders, velocity distribution within cross sections, and the relationship between flood recurrence and bankfull channel size [Leopold et al., 1964]. These studies quantified many geomorphic relationships, but they did not reveal the ' physical processes underlying those relationships. More recent work, at both large (kilometers) and small (meters) scales, has endeavored to study and model the physical processes that create channel form. ' Meanderin Rivers g ' Self-formed channels have been classified as straight, meandering, braided, or anastomosing; each planform type is a response to the interaction of discharge, sediment size and availability, and bank and bed characteristics [Rosgen, 1994; Leopold et al., 1964]. Subsequent work has shown that these forms actually describe end-members of a continuum of channel patterns that have many causes [van den Berg, 1995]. Early studies argued that braided streams typically have high sediment loads in relation to transport capacity, straight rivers have low sediment loads, and meandering rivers have approximately equal sediment loads and transport capacity [Leopold et al., 1964]. Much controversy has surrounded the origins of flow meandering. Is meandering caused ' by the deflection of current around alternate bars, causing additional deposition on the bars and erosion on the exterior of the bend, or are the barforms determined by the flow patterns? What physical properties control meander wavelength and amplitude? Rhoads and Welford [ 1991 ] noted that no universal theory of meandering initiation has emerged, although the most ' A-3