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Development of Estimated Daily FlolVs - Yampa River at Maybell Evaporation, first fill and reservoir operation depletions were calculated for Yamcolo Reservoir. The reservoir was built in 1980 and historical end-of-month storage records are available starting from January of 1981. The evaporation depletion was computed as the average surface area multiplied by the net evaporation rate. The first fill depletion was assumed to be equal to the end-of-month content for January. 1981, Le., it was assumed that the reservoir began storing water in January. 1981. Depletions from reservoir operation for the month were computed as the current end-of-month content minus the previous end-of-month content. Hence, the depletion is positive when the reservoir is storing water. and is negative when the reservoir is releasing water. Monthly depletions from evaporation, first fill and reservoir operations were then added together and dissagregated into daily values using the quadratic spline interpolation scheme. Evaporation and reservoir operation depletions were calculated for Stillwater Reservoir. The first fill depletion was not considered in this case because the reservoir was built before our study period began in 1950. An average pattern of end-of-month contents was obtained from the recent historical end-of-month records from 1979 through 1990. This pattern was then applied over the entire study period. The daily evaporation and reservoir operation depletions were then calculated as described above. Evaporation and first fill depletions were computed for all stock ponds in Districts 44. 57 and 58 in existence during the study period. The surface areas and the date of appropriation of the stock ponds were obtained from the Divisiun 6 Office of the State Engineer. From these, a time series indicating how the surface areas increased over the study period from 1950 through 1982 was constructed based upon the assumption that the stock pond was built in the year of water rights appropriation. Evaporation depletions for each month of the study period were then computed as the net evaporation rate for the month multiplied by the surface area for the year. First fill depletions were assumed to take place in the month of April when the surface area increased from one year to the next. The first fill depletion amount was computed as the reservoir volume corresponding to the increase in surface area using the area-volume relationship for Stillwater Reservoir (this was considered representative of typical reservoirs). The monthly evaporation and first fill depletions for the stock ponds were dissagregated into daily depletion values, and then routed to the Maybell gage using the appropriate travel times. River Flow Travel Times The effects of river travel times are significant when daily depletions at points upstream in the basin must be translated to the Maybell gage. Average travel times between selected points in the basin and the gage reach were estimated for each month of the year using a uniform flow assumption, channel geometries and slopes estimated from USGS quad maps, and average monthly gaged flows at the Steamboat Springs and MaybeIl gages. The resulting estimates were then used to develop daily routing factors to be used in translating estimated depletions from their locations of occurrence to the Maybell gage. Average travel times were estimated between: (I) the USGS gage on Yampa River at Craig and the USGS gage on Yampa River near MaybeIl: (2) the USGS gage on Yampa River near Steamboat and the USGS gage on Yampa River at Craig; (3) the USGS gage on Elk River at Clark and the confluence of the Elk River and Yampa River: and (4) the USGS gage on Yampa River above Stagecoach Reservoir and the USGS gage on Yampa River near 8