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<br />mouth of Split Mountain Canyon and 6.5 km. upstream from the confluence with <br />the Duchesne River (Fig. 1). The Ouray study reach is located in a wider alluvial <br />valley than elsewhere on the Green River (Fig. 1.5), has a channel pattern of <br />restricted meanders, and has a wide, well-vegetated floodplain. The channel is <br />relatively wide and has an average bankfull width-to-depth ratio of 41. The <br />slope here of .00015 m/m is the lowest of any part of the Green River. Medium <br />grained sand is--the most prevalent substrate in the reach, and a veneer of silt and <br />clay occurs along fringe and low velocity areas. Bed material at Ouray ranges <br />from clay with a .008 mm grain diameter to coarse sand with a 4.8 mm grain <br />diameter (Krider, 1994). <br />Saltcedar (Tamarix chinensis) reached the study area during the late 1950's <br />(Graf, 1978) and is now present in moderate densities. There are several <br />geomorphic effects associated with Saltcedar invasion. These include <br />stabilization and aggradation of channel features such as banks and bars, <br />attachment of islands to the bank, and increased floodplain roughness. The <br />cumulative result of these effects, which is somewhat evident at Ouray, is <br />simplification and narrowing of the channel. Native willows (Salix sp.) are also <br />in abundance throughout the study reach. <br />A map of the Ouray study reach is shown in FIGURE 3. The cross- <br />sections were first established by Andrews and Nelson (1989) in 1986, and <br />subsequently surveyed on an annual basis. Rakowski (1997) resurveyed the <br />channel 9 times between 1992 and 1994. She also established two more cross- <br />sections. Early this summer, two additional cross-sections were added, one at the <br />upstream end of the study reach and one-at the downstream end. These are <br />intended to improve model resolution by better characterizing the geomorphic <br />conditions flanking the two major bar complexes under investigation.. The <br />cross-sections are now evenly spaced at approximately 1.5 channel widths apart <br />and they extend for a channel length of approximately 2 km.. <br /> <br />7 <br />