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<br />r <br />i <br />.. <br />! <br /> <br />. <br /> <br />,. <br /> <br />" <br /> <br />SUMMARY <br /> <br /> <br />The investigation of transit losses and travel times of reservoir <br />releases along the Arkansas River from Pueblo Reservoir near Pueblo to John <br />Martin Reservoir near Las Animas, a distance of 142 river miles, can be <br />summarized as follows: <br /> <br />1. A modified-computer model, calibrated by a controlled-test release <br />from Pueblo Reservoir on September 22, 1975, simulates the response of the <br />Arkansas River and the adjoining aquifer in the study reach to the passage of <br />reservoir releases. The model produces downstream hydrographs that include <br />the effects of bank storage, channel storage, and evaporation losses. <br />Transit losses during steady-state conditions can be determined from these <br />hydrographs. <br /> <br />2. Transit losses depend on rate and duration of the reservoir release, <br />antecedent river conditions, time of year, and distance downstream from <br />Pueblo Reservoir. For a 10-day release of 100 ft3/s, the transit loss in the <br />study reach ranges from an average of 0.35 percent per mile during very low <br />antecedent streamflow conditions to an average of 0.05 percent per mile <br />during very high antecedent streamflow conditions. Transit losses for <br />releases made during November through April are about 7 percent less than the <br />losses during other times of the year because of the smaller evaporation <br />rate. Transit losses for releases made to an on-channel reservoir are only <br />10 percent of these rates if bank and channel storage are not considered as <br />true losses. Reservoir releases of less than 100 ft3/s increase the transit <br />losses as much as 6 percent, whereas larger releases decrease the losses by <br />as much as 10 percent. Similarly, releases of less than 10 days can double <br />the transit loss, whereas longer releases can decrease the transit loss by as <br />much as 25 percent. <br /> <br />3. Traveltime of a reservoir release depends on antecedent river <br />conditions and distance downstream from Pueblo Reservoir: Rates of travel <br />generally range from 0.146 h/mi near the upstrea~ end of the study,. reach <br />during high antecedent streamflow conditions, to 1.67 h/mi at the downstream <br />end of the study reach during very low antecedent streamflow conditions. <br /> <br />4. Management practices that may be used to benefit water users in the <br />study area include selecting the optimum time, amount, and duration of <br />release to minimize transit losses; using traveltime data to determine the <br />time when diversion should begin, initially diverting in increments to avoid <br />unstable streamflow conditions downstream; using transit-loss data to <br />determine the final dive'rsion rate; and reducing the diversion by increments, <br />again to prevent unstable flow downstream. <br /> <br />29 <br /> <br />......... <br /> <br />, <br />