WSP00979

• File Number: 8220.101.10.A
• Description: Colorado River-Water Projects-Glen Canyon Dam/Lake Powell-Glen Canyon Adaptive Management-AMWG
• State: AZ
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 3/3/2004
• Author: USGS
• Title: AMWG Meeting Attachments-March 3-4 2004-Computation and Analysis of the Instantaneous Discharge Record for the Colorado River at Lees Ferry-Arizona May 8 1921-Sep 30 2000
• Water Supply Pro - Doc Type: Report/Study

B.
70,000

SEPTEMBER 13, 1927, FLOOD WITH
PEAK DISCHARGE OF
125,000 CUBIC FEET PER SECOND

o 60,000
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w
a.
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50,000

CLOSURE OF GLEN CANYON DAM

DAM OPERATIONS
CONSTRAINED
ON AUGUST 1,1991

40,000

w
~ 30,000
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~ 20,000
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~ 10,000
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a

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OATE

Figure 21-Continued.(bJ The daily range in the discharge of the Colorado River at lees Ferry between May 8. 1921. and September 30, 2000

The median discharge of the Colorado River
at Lees Ferry during the entire pre-dam period was
7,980 ft3/s (fig. 22A) and discharge varied considerahly
during each of the four pre-dam decades (fig, 22B). The
decades with the highest discharges were the 1920s
and I 940s, with median discharges of 10,700 ft3/s and
8,460 ft3/s, respectively. The periods with the lowest
discharges were the decade of the 1930s and the 12-year
period betweeuJanuary I, 1951, and March 12, 1963,
with median discharges of 6,720 ft3/s and 7,210 ft3/s,
respectively, The pre-dam month with the highest
discharge was June, with a median discharge of
51,200 ft3/s; the pre-dam month with the lowest discharge
was January, with a median discharge of 5,140 ft3/s
(fig. 23 and Appendix F), Operation of Glen Canyon Dam
during 1963-2000 increased the median discharge of the
Colorado River at Lees Ferry to 12,600 ft3/s (fig. 22A), a
discharge 58 percent higher than the pre-dam median

discharge and 18 percent higher than the median
discharge during the wettest of the four pre-dam decades,
the 1920s (fig. 228).
The decadal variation iu the discharge of the
Colorado River at Lees Feny has major implications for
the accumulation and storage of sediment in the reach in
Grand Canyon National Park between the Lees Ferry and
Grand Canyon gaging stations (that is, the reach in Marble
and upper Grand Canyons). Topping and others (2000)
showed that, as a likely result of the difference in
hydraulic geomel1y between Glen Canyon and Marble
Canyon, sand-transport rates at the Lees Feny gaging
station exceeded those at the Grand Canyon gaging station
when the discharge was lower than about 9,000 ft3/s
(Topping and others, 2000, fig, 4B). At discharges lower
than about 7,000 ft3/s, more than an order of magnitude
more sand,was transported past the Lees Ferry gaging
station than p~ the Grand Canyon gaging station, and at

{)??30

Analysis of the Continuous Record of Instantaneous Discharge 43