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Draft Final Completion Report to UDWR for Contract #93-1070. Amendment 3 11 a meander exceeds a critical value (about 200) (Ikeda, 1989). Forced bars form only in response to the pattern of flow through a bend (Ikeda, 1989) and are commonly called point bars. Within the Ouray NWR, both fixed (Le., bank- attached compound) bars and forced (i.e., point) bars exist. A more transient type of bar, called a mid-channel bar, also exists in the alluvial portions of the Green River. The mid-channel and some superimposed bars of the Green River within Ouray NWR are similar to those described by Cant and Walker (1978) in the braided South Saskatchewan River of Canada. Portions of cross-channel bars emergent at low flow accrete additional sediment at low flow, creating sand flats just above base flow level. -., Floods Measuring changes in channel form during flood passage is more difficult than observing the resultant morphology at low flow. Consequently, much of our understanding of channel response to flood passage comes from measurements made at USGS gaging stations. Measurements made at USGS gage stations indicate that sand-bedded alluvial rivers typically scour on the ascending limb and fill on the descending limb, although Leopold and others (1964) noted that gage cross sections may be biased by their siting in pool sections of rivers. Leopold and others (1964) described the response of the Colorado River at Lees Ferry to the passage of the 1956 spring flood. The cross section scoured on the ascending limb with much of the discharge increase being accommodated by bed scour of approximately 3 m. The maximum depth of scour and the flood peak appeared to coincide. The bed subsequently filled on the descending limb to about the pre-flood level (Leopold and others, 1964). This pattern was typical of sand-bedded rivers at gaged cross sections. Additional work on the Rio Grande del Ranchos, a tributary of the Rio Grande in New Mexico, and Baldwin Creek and Popo Agie River in Wyoming found net scour at flood peak over long reaches containing both pools and riffles (Leopold and others, 1964). Colby (1964) found that single cross-section measurements, such as those made at gaging stations, could not be used to characterize the behavior of a stream reach. Cross sections within a single reach could be characterized as either filling or scouring cross sections, with fill or scour occurring on both the ascending and descending limb of the flood. In addition. Colby (1964) found that streamS typically adjusted to changing discharge by changes in the water surface elevation rather than by scour or till of the stream bed. Consequently, cross-section studies to characterize river response to flood passage must include cross sections spaced throughout a representative reach. For sand-bedded rivers, the bedload is typically 10 to 35 percent of the suspended sediment load (Lane and