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<br />Table 1. U,S. Geological SUlVey gaging stations used in this study
<br />
<br />Station number Official station name
<br />
<br />Shortened name used
<br />in this paper
<br />
<br />09153000 Colorado River near Fl1lita,
<br />Colorado
<br />09315000 Green River at Green River,
<br />Utah
<br />09361500 Animas River at Durango,
<br />Colorado
<br />
<br />Colorado River near
<br />Fnlita
<br />Green River
<br />
<br />Animas River
<br />
<br />09363000
<br />
<br />rlorida River ncar Durango, Florida River
<br />Colorado
<br />San Juan River near Bluff, Utah near Blurf
<br />Colorado River at Lees Ferry, Lees Feny
<br />Arizona
<br />
<br />09379500
<br />09380000
<br />
<br />09402500 Colorado River near Grand Grand Canyon
<br />Canyon, Arizona
<br />09424000 Colorado River neur Topock, Topock
<br />Arizona
<br />09521000 Colorado River at Yuma, Yuma
<br />Arizona
<br />
<br />Thus, measurements at Lees Ferry are essential to the
<br />management of water in the entire Colorado River
<br />drainage basin, These legal documents that govern the
<br />discharge of the Colorado River at Lees Ferry constitute
<br />part of the "The Law of the River" and are available
<br />electronically from the Bureau of Reelamation (Bureau of
<br />Reelamation, 2000).
<br />Widespread dcvelopment of water resources within
<br />the Upper Colorado River Basin began with authorization
<br />of the Colorado River Storage Project in 1956 (Martin,
<br />1989), Glen Canyon Dam was the largest of the dams
<br />constructed under this act. The gates of this dam were
<br />elosed on March 13, 1963, regulating the discharge of the
<br />Colorado River at Lees Ferry and initiating the storage
<br />of water in the reservoir known as Lake Powell. This
<br />reservoir tilled for the first time on June 22, 1980, and its
<br />27 million acre-foot capacity is the second largest in the
<br />United States, The largest reservoir in the United States
<br />is Lake Mead, at the downstream end of Grand Canyon
<br />(tig.1A).
<br />Dctailed analysis of the Lces Ferry discharge
<br />record is valuable for a variety of purposes, ineluding
<br />evaluation of natural hydrologic variability within the.
<br />
<br />Upper Basin and evaluation of the cffects of upstrcam
<br />dams and diversions on the discharge of thc Colorado
<br />River, Althuugh water was exported from the hcadwaters
<br />of thc Colorado River Basin as early as 1892 (Fradkin,
<br />1984), discharge at Lees Fcrry was only slightly affected
<br />by upstrcam watcr development prior to the closure of
<br />Glen Canyon Dam in March 1963. Pre-1963 depletion of
<br />water from the headwaters of the Colorado River rcsulted
<br />in only a 10-15 percent rcduction in the "virgin flow" of
<br />the Colorado River at Lees Fcrry, with very little change
<br />in the amount of water depicted horn the Upper Basin
<br />occurring betwecn ]921 and 1963 (see fig, 4 in Ferrari,
<br />1988), Thus, analysis of thc first 42 years of record
<br />at the Lecs Ferry gaging station (from May 1921 to
<br />March 1963) provides information on the quasi-natural
<br />hydrology of the Upper Basin, The following 37 years
<br />of record at the gaging station (ti'om March 1963 to
<br />September 2000) werc dominated by the effccts of
<br />upstream water development and rcgulation of discharge
<br />by operation of Glcn Canyon Dam. Analysis of this
<br />later part of the period of rccord, thereforc, providcs
<br />information on the effcct of upstream water development
<br />on the dischargc of the Colorado River in Grand Canyon
<br />National Park, bccause no large tributaries enter the
<br />Colorado River between Glen Canyon Dam and the
<br />Lees Ferry gaging station,
<br />Interest in the Lees Ferry dischargc record
<br />increascd after 1983 whcn comprehensivc environmental
<br />studies were initiated by the Bureau of Reclamation to
<br />evaluate the effect of the operation of Glen Canyon Dam
<br />on the Colorado River ecosystem downstream from the
<br />dam (U.S. Department of the Interior, 1995), Previous
<br />analysis of the hydrologic effects of dam opcration
<br />involved visual comparison of the record of stage and
<br />dischargc for somc years (Turner and Karpiscak, 1980),
<br />and visual and statistical comparison of post-dam
<br />bi-hourly, hourly, or 30-minute discharge data with pre-
<br />dam daily mean dischargc data (V,S, Dcpartment of the
<br />Interior, 1995), Thcse analyses were hindcred by the fact
<br />that only daily mean discharge data at the Lees Fcrry
<br />gaging station were available prior to February 2,1967,
<br />and 30-minute discharge data werc only available after
<br />October I, 1986. Thus, the valuc of these analyses was
<br />limited bccause pre-dam and post-dam hydrologic data at
<br />the Lecs Ferry gaging station were not of comparablc
<br />precision.
<br />
<br />1
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<br />1
<br />1
<br />t
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<br />
<br />6 Computation and Analysis of the Instantaneous-Discharge Record 'urthe Colorado River at Lees Ferry. Arizona-May 8. 1921. through September 30, 2000
<br />
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