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<br />1949 <br /> <br />Arkansas River at Las Animas <br /> <br />. <br /> <br />Station 07124000 (Arkansas River at Las Animas) is located about 120 mi downstream from Pueblo Reservoir <br /> <br />(fig. 1). Discharge at this station is substantially smaller than at station 07109500 (fig. 3). because several large irri- <br /> <br />gation canals divert mosl oflhe discharge in Ihe 96 mi reach berween slations. Irrigation rerum flow comprises a <br /> <br />substantial fraction of the discharge at station 07124000 (Cain, 1987), therefore, the specific conductance is consid- <br /> <br />erably higher than at upstream sires (fig. 4). Discharge and specific-conductance data were available at station <br /> <br />07124000 for 1961-94. <br /> <br />The median annual discharge at station 07124000 increased significantly (p=O.O I) from 77;200 acre-ft/yr in <br /> <br />1961-74 to 149,400 acre-ftlyr in 1975-94. This difference represents, on average, an increase in discharge of about <br /> <br />\00 fI3/s/day. Pan oflhe increased annual discharge may be attributed to increased inflow from the upper basin. The <br /> <br />median annual discharge that entered the lower basin from the upper basin, as indicated by the record at station <br /> <br />07096000, increased from 5 I 3,500 acre-ft in 1961-74 to 538,600 acre-ft in 1975-94 or on ayerage about 35 ft3/s/day. <br /> <br />. <br /> <br />The daily discharge at station 07\24000 increased in every month after 1974 (fig. 17); the differences in dis- <br /> <br />charge were significant for all 12 months (table 9). Increases in discharge for November through March are largely <br /> <br />attributable to the fact that there ha~ been a substantial decrease in the amount of water thar was divened and applied <br /> <br />to fallow fields in the winter months. Additionally, as pan of the WWSP and the 1980 Operating Plan for John Mar- <br /> <br />tin Reservoir, three large irrigation canal companies have been allowed to store winter-season water in John Manin <br /> <br />Reservoir, as an alternative to storage in Pueblo Reservoir or in private off-channel reseryoirs. Prior to these <br /> <br />changes. winter flows at station 07124000 were diminished by the upstream diversion and consumptive use of this <br /> <br />water. The increase in discharge during the growing season (April - October) is attributable to several factors, <br /> <br />including the following: (I) The release ofWWSP water from Pueblo Reservoir; and (2) increased inflow from the <br /> <br />upper basin and from Fountain Creek. <br /> <br />. <br /> <br />:OREUMiNARV'REPOF(t <br />, t:'J/~!r' . <br />,:::118JECTTO R.._. :..". <br />..........." <br /> <br />29 <br />