WSP10461 - Laserfiche WebLink

Home Browse Search

II ; ,. TRAVELTIME OF RESERVOIR RELEASES . In order to analyze the traveltime of reservoir releases in the study reach from Pueblo Reservoir to John Martin Reservoir, accurate determinations of river-mile locations for major diversion points and gaging stations were necessary, These determinations were made using the latest U.S. Geological Survey topographic maps and are tabulated in table 1. Traveltime information was primarily obtained from streamflow records of historical reservoir releases. Rainfall and changes in ditch diversions or return flows also produce abrupt discharge changes along the main stem that can be followed downstream using the stage records obtained at stream-gaging stations. The data selected were limited to releases or other discharge changes occurring after a period of relatively stable streamflow conditions to insure that the average antecedent discharge would be representative of the subreach. This type of traveltime, commonly known as wave celerity, is approximately 1.5 to 2.0 times the mean traveltime under a steady-state condition. After determining the traveltime of more than 50 distinguishable stage changes occurring in the study reach since 1970, relationships between traveltime and antecedent subreach streamflow were developed for each of the six subreaches. The results of this analysis are summarized in table 6, which also gives an example of how the traveltime of a reservoir release to a particular diversion point can be determined. Rates of travel of reservoir releases in the study reach range from 0.146 h/mi in subreach 1 when the average antecedent streamflow is 3,000 ft3/s, to 1.67 h/mi in subreach 6 when the average antecedent streamflow is 10 ft3/s. LIMITATIONS AND ACCURACY OF TRANSIT-LOSS AND TRAVELTIME RESULTS The transit-loss results shown in tables 4 and 5 are based on the calibrated computer" model, as modified for the study reach. Because this model simulates response only during steady-state conditions, the transit- loss determinations are an approximation for unsteady-state conditions during the reservoir-release period, such as changes in tributary inflows, canal diversions, or water-table conditions. The accuracy of model results for release or river conditions significantly different from those that existed during the calibration release of September 22, 1975, is uncertain. Indications are that transit-loss results are accurate within 6 percent in the general range of these conditions. The traveltime information shown in table 6 is similar to transit-loss results in that it is valid only for the steady-state conditions on which it is based. Although the recorded data common.1y indicated traveltime differ- ences of at least 6 hours for a particular average antecedent streamflow, they were generally within 30 percent of the average subreach traveltime shown in table 6. Because of limited data for antecedent streamflows greater than 2,000 ft3/s in subreaches 1-3, and greater than 600 ft3/s in subreaches 4-6, the accuracy of the data in table 6 is uncertain for discharges greater than these values. 21 .--. ,