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<br />22 <br /> <br />: J <br />"-'1 <br />~::j <br /> <br />I <br /> <br />I <br /> <br />-,"'I <br />" <br /> <br /> <br /> <br />~,' <br />~~ <br />>..1 <br /> <br /> <br />"""""',1 <br />~ <br />J <br />J <br />d <br />~] <br />.J <br />J <br />:] <br />1 <br />j <br />J <br /> <br />Chapter 3 <br />HISTORIC CHANGES IN STREAMFLOW <br /> <br />INTRODUCTION <br />Flows of the upper Colorado River have decreased in magnitude <br />over the past 60 years (Liebermann et al., 1989), and it is generally thought <br />that this has had a major impact on endangered fishes (Osmundson and <br />Kaeding, 1991). This chapter explores the history of changes in the flow <br />regime in the upper Colorado River basin. This work includes an <br />inventory of water development above the study site, and an analysis of <br />historic changes in the duration, timing, and magnitude of peak and mean <br />annual flows. Both dammed and free-flowing tributaries of the upper <br />Colorado River are considered, as well as the mainstem of the Colorado <br />River from its headwaters to the study area. <br /> <br />Flow Trends and Water Development <br />Flow data were retrieved from U.S. Geological Survey (USGS) water <br />supply papers and from CD-ROMs which contain files from the USGS <br />W A TSTORE data base. The records were used for three purposes. First, <br />the flows of unregulated rivers in the region were analyzed to determine <br />trends in streamflow throughout the century. These results are essential <br />for separating the effects of climate and water development on regulated <br />rivers. Secondly, the effect of dams on streamflow in the basin were <br />