Colorado Water Resources Circular No. 20

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� 0753 determined by noting the time when the first perceptible rise in stage occurred on the gage height charts for either the "near Pueblo" (07099500) or "Avondale" (07109500) gaging stations, and adding to this a computed time of travel from these stations to the canal headgates. This computed time of travel from these two stations to the canal head - gates was based on field measurements of mean river velocity at various river discharges. Figure 3 also notes that for releases from Turquoise Lake 412 hours must be added, and for releases from Clear Creek Reservoir 2z hours must be subtracted, to determine travel time to the Colorado Canal headgate. These figures are based on field observations, streamflow measurements, and gaging- station records. The discharge scale on figure 3 shows the streamflow at the "near Wellsville" gaging station (07093700) immediately prior to the time of release. The discharge at this particular station was chosen as an index for the entire reach for the following reasons: (1) analysis of past records indicated the discharge at the. "near Wellsville" station best approximates the average flow in the reach, (2) this gaging station is equipped with an instrument by which the stage can be determined by telephone, (3) the stage- discharge relationship is relatively stable, and (4) there are no diversions which bypass the station. The stage discharge relationship for this gaging station is given in table 2. SOURCES OF TRANSPORTATION LOSS Colorado water law allows owners of reservoirs to use natural streams to transport their water provided allowances are made for transit losses (Radosevich and Hamburg, 1971). Transportation loss, or transit loss, refers to released water that cannot be utilized at the downstream delivery point. The transit loss currently being charged for the Arkan- sas River is 0.07 percent of the reservoir release per mile of river. Reservoir releases down the upper Arkansas River typically range from 300 to 500 ft /s for a duration of from 6 to 14 days. During these periods, the release water can temporarily be retained in channel and bank storage, inadvertently diverted, or evapotranspired. Only evapo- transpiration removes water from the stream system and, therefore, can be considered a true loss. Channel - storage, bank storage, and inadvert- ent diversions may or may not be other sources of transportation loss. During the past 2 years, a careful study has been made of channel and bank storage, inadvertent diversions, and evapotranspiration, and their effects on reservoir releases from Twin Lakes Reservoir to the Colorado Canal headgate. The following discussions report the findings of this study. r 9