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<br />. <br /> <br />. <br /> <br />I. <br /> <br />I. <br /> <br />I <br />:. <br /> <br />. <br /> <br />. <br /> <br />I <br />. <br /> <br />I. <br />I <br /> <br />~ <br />, <br /> <br />. <br /> <br />. <br /> <br />--- <br /> <br />29. ARKANSAS RIVER FREQUENCIES. Dischar!te freq\lE'ncy curves <br />for the Arksnsas River between Pueblo and Las Animas were dpvelol'l'd <br />where streamflow records are avail.able and below IM.inr trihutaries. <br />Records are available at Avondale, Nepesta, La Junta, and l.as Ani- <br />mas. The gage record at Avondale was discarded, however, heCA\lBe <br />irrigation diversions and returns have a significant effect on thl' <br />lower flows, at that site, and could not be accounted for. At <br />Nepesta, La Junta, and Las Animas, frequency curves were computed <br />using a log-Pearson Type III analysis in accordance with WRC Bulle- <br />tin 17. Discharge records prior to construction of Puehlo Reservoir <br />were adjusted to reflect operation of the reservoir and present con- <br />ditions. These adjustments were made by taking each annual peak <br />separately and determining the most prohable storm centering from <br />rainfall and stream gage data. If the atorm was centered below the <br />dam, no adjustments were made. If the storm was centered above the <br />dam, adjustments were made to safe channel capacities with consider- <br />ation given to downstream existing flows. If downstream flows were <br />above channel capacity, no releases were considered and the flows <br />were adjusted accordingly. During low flow conditions, irrigation <br />releases were assumed and in many cases, this WAS the peak discharge <br />for the year. All ad.1ustments of flows through Puebln Reservoir <br />were done in accordance with the Pueblo Dam and Reservoir Master <br />Water Control Manual which ia presently beinr, completed. The dis- <br />charge frequency curves for the Arkansas River at Nepesta, La Junta, <br />and Las Animas are shown on Plates 5, 6, and 7, respectively. The <br />frequency curves on the Arkansas River below 1l\ll.10r tr:lhutartes arc <br />shown on Plates 8 and 9. A discussion on the development of eRc" <br />curve is presented on the following paragraphs. <br /> <br />a. Arkansas River Below Fountain Creek. This frequency curve <br />is the result of flows from Fountsin Creek and concurrent flows in <br />the Arkansas River. Concurrent flows for the standard project flood <br />were determined from the standard project storm isohyetal pattern <br />over Fountain Creek. For other floods of designated frequency, <br />ratios of the SPF to frequency floods on Fountain Creek were applied <br />to the computed SPF concurrent flow. Releases from Pucblo Reservoir <br />were assumed to be zero in accordance witb established regulation <br />procedures. <br /> <br />b. Arkansas River Below St. Charles River. This curve was <br />developed by routing the frequency curve below Fountain Cree~ to <br />this location. Routings were performed by the Modified PuIs method. <br />A check was made for concurrent flows from the St. Charles River us- <br />ing the standard project storm and were found to be ner,li~ible. <br />Also, various storm centerings were considered but the adopted fre- <br />quency curve proved to be critical. <br /> <br />c. Arkansas River Below Chico Creek, Below Huerfano River, and <br />Below Apishapa River. To determine the discharFe frequency curves <br />at these locations, the standard project flood was utUized. The <br /> <br />11 <br />