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i Site Descriptions Site selection was based on accessibility, location with respect to other level loggers and USGS gages in the Green River system and the apparent need for a discharge hydrograph. Relatively stable cross sections sites were selected for the level loggers. Constrictions, alluvial channel characteristics, sediment deposition and scour and potential hydraulic controls were all considered during the site selection process. Each site was selected to reduce the unmonitored reaches to less than 90 miles. Figure 1 shows the approximate locations of the level loggers and Gwen River gaging stations with their corresponding distance in river miles upstream of the confluence of the Colorado River. The major tributaries in the system are also shown on the figure. Prior to 1995, the only available discharge data in the Green River downstream of the confluence with the Yampa River was collected by the USGS gage stations at Jensen and Green River. These were the only two stream gages in approximately 350 river miles with numerous intervening tributaries. The various sites are described below. Mitten Park The Ievel logger was installed downstream of the confluence of the Yampa and Green Rivers in Mitten Park on river left. This site was a previous river gaging site for the Fish and Wildlife Service which used a strip chart recorder and well to monitored the water surface elevation. The channel is this reach is an alluvial bed upstream of the entrance to Whirlpool Canyon. The cross section is located at slight channel constriction with a large rock outcropping along the right bank providing the hydraulic control. Jensen Gage The Jensen is located at the bridge crossing the Green River just downstream of the Split Mountain Campground in Dinosaur National Park. This gage has been in continuous operation since 1947. The discharge measured at this gage is essentially the flow through the downstream reach to Ouray except for a few small ephemeral tributaries. This gage is located at a relatively stable cross section with a cobble bed channel, but is subject to fluctuations in the rating curve. In 1996, stage shifts were noted of +3.3 on April 18, +2.1 on Apri130, +1.1 on May 16, +1.9 on May 2l ,and 0.0 on June 26 indicating a 3.3 ft variation of the stage discharge relationship from April 18 to June 26. Oirray National Wildlife Refuge A strip chart recorder was installed at the Ouray Wildlife Refuge in an existing monitoring well near the near fish hatchery. This site has been monitored in the past for water surface elevations and discharge. The discharge measured at this site represents the flow through the flooded bottomland sites from Bonanza Bridge to the confluence with the Duchesne River. The river channel at this location is relatively stable with a cobble bed on the right portion of the channel. Tl~e channel is positioned on the far western extent of the floodplain against the river valley bluffs. A level logger is recommended for this site in future years. 2