WSP10382 - Laserfiche WebLink

Home Browse Search

At the Maybell station, suspended sediment is predominantly in the silt and clay.size range (particle diameter is less than 0.062 mm). At the Lily station, most of the suspended sediment also is in the silt and clay-size range, but about 40 percent is sand size (particle diameter is larger than 0.062 mm, and smaller than 2.00 mm). The size and quantity of sediment transported by the Yampa and Little Snake Rivers are reflected in the appear- ances of their channels at the gaging stations and downstream before their confluence at Lily Park. The Yampa River, above the confluence, has a well- defined channel with cobble bed and point-bars; the banks are steep and composed of silt and clay-size material. By contrast, the Little Snake River has a bed composed predominantly of sand-size material. Where the river is not confined by bedrock or resistant banks, the channel has numerous braids and transverse channel bars that are exposed at i ntermedi ate and low flows. Downstream from the confluence with the Little Snake River, and upstream from the beginning of the Yampa Canyon, the geomorphology of the, Yampa River is conspicuously affected by the high sediment contribution from the Little Snake RiVer. Along this reach the Yampa River has a shallow, anastomosing channel and a bed composed of sand-size material. STREAMFLOW OF THE YAMPA RIVER AT DEERLODGE PARK A streamflow-gaging station was established in 1982 in Deer10dge Park by the U.S. Geological Survey to obtain data for determining annual streamflow and sediment transport into the Yampa Canyon (fig. 3). The gaging station is located approximately one-half mile upstream from the entrance to the Yampa . Canyon. River stage at this station, 09260050 Yampa River at Deer10dge Park, was continuously recorded from April 1982 through September 1983. The rela- tion between water-surface elevation and discharge was determined from 35 discharge measurements (Carter and Davidian, 1968). Discharge measurements were ,made from a boat attached to a fixed cable or by wading. Measured discharge ranged from 646 ft3/s to 17,600 ft3/s, and shifting of the sand bed occurred between most measurements (fig. 4). Hydraulic geometry relations based on di scharge measurements made at thi s site are presented in tab 1 e l. The low value of the exponent (0.059) in the equation of channel width versus discharge resulted because banks at the stUdy section were vertical and resistant to erosion; hence, channel width varied little with discharge. Most adjustment to increasing discharge occurred as change in mean depth and mean flow velocity. Water-surface profiles were surveyed on 12 days when the discharge varied from 930 ft3/s to 15,800 ft3/s. Although the average slope of the reach varied from 0.00040 ft/ft to 0.00087 ft/ft, no consistent rela- tion between water-surface slope and discharge was apparent. Slope values varied about a mean of 0.00069 ft/ft with a standard deviation of 0.00014. Daily mean discharges recorded at the Yampa River at Deerlodge Park gage were compared to the sum of daily mean discharges recorded at the Little Snake River near Lily gage and the {ampa River near Haybell gage. The concurrent p~~'iod G; recof'd for these th~"2e gagiilg staticns ~'12S 548 days, and incluc2d peak-f1o\v months for both 1982 and 1983, Daily mean discharges at Dee.rlodge Park ~ere found to be highly correlated with the sum of daily mean discharges 6