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5. To estimate the mean annual sediment load transported through Deerlodge Park and into Yampa Canyon for various assumed reductions in streamflow. ~ To establish a method to predict changes in the sedlment budget at Deerlodge Park, if the streamflow frequency distribution, annual streamflow, or annual sediment supply are altered or reduced. 4. HYDROLOGY OF THE YAMPA RIVER BASIN Streamflow data are collected by the U.S. Geological Survey at several locations in the Yampa River basin. Two .streamflow-gaging stations upstream from the study reach, 09251000 Yampa River near Maybell and 09260000 Little Snake River near Lily have recorded over 60 years of discharge data from a combined area that represents 89 percent of the entire Yampa River basin (fig. 1). Mean-annual streamflow is 1.1 million acre-ft/yr at the Maybell site, and 0.4 million acre-ft/yr at the Lily site. Timing and volume of floodflows at both sites are predominantly a func. tion of snowmelt; however, in late summer the streamflow occasionally is influenced by rainstorms. Peak flows for both rivers usually occur between mid-May and mid-June. Extremes for the period of record are 17,900 ft3/s on May 19, 1917, for the Yampa River near Maybell, and 14,200 ft3/s on May 27,,1926, for the Little Snake River near Lily. Hydrographs depicting mean daily discharges averaged over the period of record for these two sites are presented in figure 2. Gaging stations 09251000 Yampa River near Maybell and 09260000 Little Snake River near Lily are on main-stem rivers draining subbasins of roughly equal area; 3,410 mi2 for the basin above the Maybell site, and 3,730 mi2 for the basin above the Lily site. The two subbasins, however, have striking differences in annual runoff and sediment yield. The Yampa River basin above Maybell contributes 73 percent of the annual streamflow and 27 percent of the annual sediment load of the entire Yampa basin. Conversely, the Little Snake River basin above Lily contributes only 27 percent of the annual streamflow but nearly 69 percent of the annual sediment load (Andrews, 1978). Suspended-sediment concentrations have been sampled periodically at the Maybe 1 1 and Lily stations. Daily suspended-sediment discharge (ton/d) is computed by multiplying the daily mean suspended-sediment concentration (mg/L) by the daily mean water discharge (ft3/s) and by a coefficient that is based on the unit of measurement of water discharge, and that assumes a specific weight of 2.65 for sediment (Porterfield, 1972). Annual suspended-sediment discharge may be computed from these data by summing daily suspended-sediment discharges when records are sufficient, or by comoining the relation between sediment discharge and \"ater discharge with a long-term streamflow-duration curve eMi 11 er, 1951). 4