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<br />1924 <br /> <br />River have been well documented (Miles. 1977; Cain, 1984; Cain, 1987), the effects of mainstem reservoir opera- <br /> <br />eons on specific conductance have not been systematically studied and reported. <br /> <br />Beginning in 1988, the U.S. Geological Survey initiated a basin-wide study of water quality in the Arkansas <br /> <br />River and the effects of certain water-supply operations on water quality. This report is the result of one element of <br /> <br />that srudy. The srudy was conducted in cooperation with the Ciry of Colorado Springs, Department of Utilities; <br /> <br />Pueblo Board of Water Works; Southeastern Colorado Water Conservancy District: Pueblo County, Department of <br /> <br />Planning and Development; Ciry of Aurora. Department of Utilities: S1. Charles Mesa Water District: Upper Arkan- <br /> <br />sas Area Council of Governments; Upper Arkansas Water Conservancy District; Ciry of Pueblo, Department ofUtil- <br /> <br />ities: Pueblo West Merropolitan District; Fremont Sanitation Disrrict: and the Cities of Rocky Ford, Las Animas and <br /> <br />Lamar. <br /> <br />PRELIMINARY REPORT <br />nU8JECT TO REVlS~C" <br /> <br />Purpose and Scope <br /> <br />. <br /> <br />This report presents, (1) step-trend results for discharge and specific conductance at three mainstem Arkansas <br /> <br />River gaging stations located between Pueblo Reservoir and John Martin Reservoir and at two mainstem stations <br /> <br />located between John Martin Reservoir and the Colorado-Kansas State line, and (2) a determination of whether sig- <br /> <br />nificant discharge and specific-conductance trends are related to the operations of these reservoirs. Long-term dis- <br /> <br />charge trends were evaluated at five mainstem gaging stations in the lower Arkansas River Basin for which there <br /> <br />exists concurrent specific-conductance data (table I). Additionally. discharge and specific-conductance trends were <br /> <br />evaluated at station 07096000. which is in the upper basin about 28 mi upstream from Pueblo Reservoir (fig. I). This <br /> <br />station was included in the analysis to help differentiate between trends in the lower valley that were caused by dif- <br /> <br />ferences in the quantity or qualiry of inflow from the upper basin or by reservoir operations within the lower basin. <br /> <br />Although. specific-conductance trends were the main focus of this study. The analysis of discharge trends was con- <br /> <br />ducted because discharge and specific conductance are typically strongly correlated, therefore, changes or trends in <br /> <br />eecific conductance can often be explained in terms of the associated change or trend in discharge. <br /> <br />5 <br />