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<br />The abundance of subaerial alluvial sediment in the Green River downstream from the <br />Lodore Ranger Station is less uniform than in the Little Snake or Yampa rivers. The <br />relative abundance of alluvial deposits varies from less than 10 to more than 80 percent of <br />the visible channel boundary between the Lodore Ranger Station and the downstream end <br />of the study reach at River Mile 194. The regional structural geology and lithology at <br />river level may be significant in determining variations in canyon-floor width and <br />gradient which influence the relative abundance of alluvial deposits in the Green River. <br /> <br />Sediment data from five sites in the Yampa River Basin and the Upper Green River Basin <br />have been collected by the USGS during an ongoing, multiyear study that began in 1998, <br />These data were augmented with sediment data gathered at these sites in earlier years as <br />part of other USGS studies and routine data collection activities. The sampling sites are: <br />(1) Yampa River above Little Snake River, near Maybell, Colorado, 09251100; <br />(2) Little Snake River, near Lily, Colorado, 09260000; <br />(3) Yampa River at Deerlodge Park, 09260050; <br />(4) Green River above Gates of Lodore, Colorado, 404417108524900 (nearest streamflow <br />gage, Green River near Greendale, Utah, 09234500); and <br />(5) Green River near Jensen, Utah, 09261000. <br /> <br />The period of record, number of samples, and type of sediment analyses vary at each of <br />the sites~ The sites with the shortest periodsofrecord are the Yampa River above Little <br />Snake River (1998-2000) and the Green River above Gates of Lodore (1999-2000); both <br />sites data include suspended and bedload measurements. Suspended-sediment <br />measurements were made at the Little Snake River, near Lily site in 1994-98 and in 2000; <br />however, no bedload measurements were made. Suspended- and bedload-sediment <br />measurements were made at the Yampa River at Deerlodge Park site in 1982-83 and <br />1998-2000, and only suspended-sediment measurements were made in 1994 and 1997. <br />Suspended-sediment measurements were made at the Green River near Jensen site from <br />1948-79. These data were analyzed by Andrews (1986) but are not included in this <br />report. Suspended- and bedload-sediment measurements were made at the Green River <br />near Jensen site from 1996-2000. Sediment load by particle-size range and by <br />hydrograph season also were computed for part of the record at all sites. <br /> <br />One objective of this study was to identify future data needs for improving the accuracy <br />of sediment-transport relations that can be used in calculating sediment budgets at the <br />five sampling sites. Sediment-transport curves were derived by least-squares regression <br />of logarithmic-transformed data to provide a means to estimate seasonal and annual <br />sediment supply to the principal streams in the upper part of the watershed (the Yampa <br />River, the Little Snake River, and the Green River upstream from the Gates of Loclore) <br />and on the Green River just upstream from a critical spawning habitat near Jensen, Utah. <br />These transport curves can be revised as additional data from the ongoing sampling <br />program become available. <br /> <br />85 B44 <br />