<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information presented in this paper is from unpublished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.
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<br />Phvsical Characteristics of the Lees Ferry Gaging Reach 7
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