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<br />Purpose and Scope <br /> <br />1bis paper describes the results of a study that had <br />three main goals. The first goal was to reanalyze, and <br />revise if necessary, the record of floods for the peliod <br />prior to construction of Glen Canyon Dam. The second <br />goal was to rectify the differing precision between the <br />various parts of the Lees Ferry gaging-station record <br />by developing a continuous record of instantaneous <br />discharge for the entire period of gage record (May 8, <br />1921, through September 30,2000), This computed <br />record of instantaneous discharge is perhaps the longest <br />(almost 80 years) high-resolution (mostly 15- to 30- <br />minute precision) times series of river discharge available <br />for any river in the world, As used iu this paper, the term <br />"instantaneous discharge" is defined as the discharge of <br />the river at any given instance in time, 111e third goal was <br />to fully describe the hydrologic characteristics of the <br />Colorado River at Lees Ferry during the pre- and post- <br />dam eras, and the implications for sediment transport and <br />storage in the reach downstream from Lees Ferry in Grand <br />Canyon National Park, through analyses of flow duration, <br />sub-daily discharge variability, and flood frequency, These <br />analyses were conducted on the Lees Ferry instantaneous <br />dischm'ge data for May 8,1921, through September 30, <br />2000, the available pre-gage historical flood data, and the <br />4,500-year paleoflood data of O'Connor and others <br />(1994). <br />It is anticipated that the basic data presented in this <br />paper will be of value for a wide range of subsequent <br />analyses by scientists and engineers. Most of the <br />information presented in this paper is from unpublished <br />USGS reports and gaging-station tec!mical files stored in <br />the Federal Records Centers, and was not previously <br />accessible to the public, A complete list of all USGS files <br />used in this paper and where they are stored is appended <br />(Appendix A), The previously unavailable stage and <br />discharge data presented in this paper can be either <br />requested from the USGS Grand Canyon Monitoring and <br />Research Center, Flagstaff, Arizona, or obtained <br />electronically at http://www.gcnn'c.gov, <br /> <br />Acknowledgments <br /> <br />Funding for this study was provided by the Grand <br />Canyon Monitoring and Research Center through a <br />cooperative agreement with Utah State University and the <br /> <br />National Research Program of the USGS, Lisa Dierauf <br />did much of the early work on digitizing the first 10 years <br />of the strip-chart record from the Lees Feny Gage, <br />Thoughtful reviews of earlier versions of this paper were <br />provided by James Bennett, Randolph Parker, Theodore <br />Melis, David Jay, John Gray, and James O'Connor. <br /> <br />PHYSICAL CHARACTERISTICS OF THE <br />lEES FERRY GAGING REACH <br /> <br />The Lees Ferry gaging station on the Colorado <br />River is located at the downstream end of Glen Canyon, <br />and just upstream from Marble Canyon. Marble Canyon <br />extends from Lees Ferry to the mouth of the Little <br />Colorado River, and Grand Canyon extends from the <br />mouth of the Little Colorado River to the Grand Wash <br />Cliffs above Lake Mead reservoir (fig.IA). On the basis <br />of the convention of Topping and others (2000), that <br />pOltion of Grand Canyon between the mouth of the Little <br />Colorado River and the Grand Canyon gaging station <br />in fig, IA is referred to as upper Grand Canyon, Today, <br />there m'e only a few abandoned stone buildings and some <br />recreational boating facilities at Lees Ferry. Between 1872 <br />and 1929, however, this ferry crossing was the only point <br />within hundreds of miles where wagons or vehicles <br />could cross the Colorado River, or where boats could be <br />launched (Rusho and Crampton, 1992; Reilly, 1999), <br />A nem'by farm, the Lonely Dell Ranch (fig. IE), was <br />occupied from 1871 until 1974, and buildings at Lees <br />Ferry, including the house and laboratory of the USGS <br />hydrographer (fig. I C), were occupied until 1976 (Reilly, <br />1999). <br />The physiography of the Lees Ferry area is <br />determined by the regional structure of the Echo Cliffs <br />monocline, which crosses the Colorado River nearby. The <br />upstream dip of the monocline brings the highly erodible <br />Moenkopi and Chinle Fonnations to liver level here <br />(Hereford and others, 2000), and the Colorado River can <br />be easily reached by following bedding planes within <br />these formations to the river's edge. In addition, Lees <br />Ferry is also made accessible, because the Pmia River has <br />eroded an open valley in the Moenkopi Formation I mile <br />downstream from the old ferry crossing on the Colorado <br />River. <br /> <br />02248 <br /> <br />Phvsical Characteristics of the Lees Ferry Gaging Reach 7 <br />