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1945 ?REUM1NARY fiEPc.::,,::.- .'.~l JO 'Ef'T TO R-' f''-'''- . ..... {i,.,; v _ t-~,. .....-' .Arkansas RIver near Avondale Station 07109500 (Arkansas River near Avondale) is located about 24 mi downstream from Pueblo Reservoir (fig. 1). The largest mainstem discharge in the Arkansas River occurs at this station because of substantial tributary inflow from the SI. Charles River and Fountain Creek and because the gage is upstream from most of the large irri- gation canals that diven a majority of the flow from the lower Arkansas River. Discharge at station 07109500 is strongly influenced by Pueblo Reservoir operations because of its proximity to Pueblo Reservoir and the absence of substantial discharge diversions between the reservoir and station 07109500.10 tenns of water quality, most of the concern and focus at this station are related to specific conductance and the suitability of the river as an agricultural irrigation supply. Discharge and specific-conductance data were available at station 07109500 for 1969-94. The median annual discharge increased insignificantly (p=0.65) from about 623,000 acre.ft in 1969-74 to about 625,200 acre-ft in 1975-94. Likewise, the median annual discharge from the upper basin, as indicated by the record at station 07096000, increased from about 535,700 acre-ft in 1969-74 to about 538,600 acre-ft in 1975-94. . Although the median annual discharge did not change significantly between 1969-74 and 1975-94, the temporal nature of discharge changed appreciably during the two periods (fig. 13). After the construction of Pueblo Reservoir (1975), discharge typically increased during March through October and decreased during November through Feb- ruary (fig. 13). The decreases in daily discharge during November through February were all statistically significant; discharge increased significantly during March, April, June, August, and October. (table 7). The decreased winter discharge was caused by the Storage of water in Pueblo Reservoir as pan of the WWSP The significant increase in discharge during March and April is partly attributable to the release of WWSP water from Pueblo Reservoir. Increased inflow from Fountain Creek also accounts for some of the increased discharge. The median annual dis- charge at the tributary gaging station 07106500 (Fountain Creek at Pueblo) increased from 45,500 acre-filyr in 1969-74 to 66.700 acre-filyr in 1975-94. Fountain Creek contributed about 8% of the annual discharge at the Arkan- sas River near Avondale in the 1969-74 and about II % in 1975-94 periods. A substantial percentage of the flow in Fountain Creek is derived from wastewater-treatment-plant eftluent from Colorado Springs and several smaller · .. all' . ElP C mwuclp ues m aso ounty. 25