|
<br />140,000
<br />130,000
<br />o
<br />5 120,000
<br />~ 110,000
<br />(fJ
<br />a: 100,000
<br />w
<br />~ 90,000
<br />w
<br />~ 80,000
<br />~ 70,000
<br />6 60,000
<br />;;; 50,000
<br />w
<br />a! 40,000
<br />:e 30,000
<br />()
<br />~ 20,000
<br />10,000
<br />o
<br />o
<br />
<br />B.
<br />
<br />o 1921-62 DISCHARGE MEASUREMENTS
<br />- SMOOTHED CURVE FIT TO MEASUREMENTS
<br />
<br />
<br />5
<br />
<br />10
<br />
<br />15
<br />
<br />20 25 0 5
<br />STAGE, IN FEET
<br />
<br />25
<br />
<br />c.
<br />
<br />..,...... SMOOTHED CURVE FIT TO 1921- 62 OATA
<br />-SMOOTHED CURVE FIT TO WATER. YEAR
<br />1921- 22 DATA ONLY
<br />
<br />.-
<br />
<br />
<br />REVERSAL IN CURVATURE
<br />
<br />10
<br />
<br />15
<br />
<br />20
<br />
<br />Figure 4-Continued. Flattening water-surface profiles with increasing stage and the reversal in curvature of the stage-discharge rating curve.
<br />(81 Stage.discharge rating curve al the lees Ferry Gage defined by 4,114 discharge measurements made between August 3. 1921. and December 30.
<br />1962, Excluded from this figure are: (11 the data after 1962 because of the influence of Glen Canyon Dam. (2) the 29 pre.dam discharge measurements
<br />affected by ice, and (3) the 1 discharge measurement made on August 2, 1929, while backwatered flow conditions existed at the gage as a result of
<br />a large flood on the Paria River. ((;1 Smoothed curve fit to the data in part B (without the data plotted) showing the reversal in curvature that occurs
<br />at a stage of about 15 feet. As shown in part A this reversal in curvature arises as the water-surface profile flattens in the OJ-mile-Iong reach
<br />immediately downstream from the gage as the hydraulic control shifts downstream. Also plotted is the smoothed curve fit to only the 193 non ice-
<br />affected measurements made during the first 14 months of gage operation during water years 1921 and 1922. Although the stage-discharge rating
<br />curve varied from year to year, this graph illustrates that the mean 1921-62 and the 1921-22 rating curves were nearly identical.
<br />
<br />used to compute daily mean discharges at Lees Ferry prior
<br />to May 7, 1926, so the revision greatly improved the
<br />accuracy of the 1921-26 daily mean discharge data.
<br />Gatewood and Hunter used this approach to recompute
<br />the daily mean discharge for the following days: June 26,
<br />1921. through September 10, 1921; April 22, 1922,
<br />through July 17, 1922; April 17, 1923, through July 31,
<br />1923; April 8, 1924, through July 16, 1924; April I, 1925,
<br />through July 21, 1925; and. April 16, 1926, through July
<br />20, 1926. On the basis of their computations, only the data
<br />with the largest errors, that is, the data from water years
<br />1921 through 1923, were revised and republished by the
<br />USGS in Grover and others (1939).
<br />At stages higher than about 19 to 20 ft (that is,
<br />discharges higher than about 110,000 to 120,000 ft3/s),
<br />the gravel bar at the mouth of the Paria River is almost
<br />overtopped (fig, 5C), and the progressive flattening
<br />of the water surface propagates upstream past the Lees
<br />Ferry Gage (fig. 6), At stages above 20 ft, the water-
<br />surface slope in the reach upstream from the gage is
<br />approximately equal to the water-surface slope in the
<br />
<br />reach downstream from the gage (fig, 4). A. Wilson
<br />(unpublished USGS analysis. April 20, 1962) compared
<br />the stage-discharge rating curves of the Lees Ferry
<br />Gage and the Lower Staff Gage and concluded that the
<br />hydraulic control for both gages was the same at stages
<br />above about 25 ft. Therefore, the decrease in the water-
<br />surface slope in the reach above the Lees Ferry Gage at
<br />stages between 20 and 25 ft is caused by the progressive
<br />development of backwatered flow conditions in the reach
<br />downstream from the gage, as the hydraulic control for
<br />the gage shifts farther downstream.
<br />Although its precise location is not known, the
<br />likely hydraulic control for the Lees Ferry Gage at stages
<br />greatly iu excess of 20 ft is either at Badger Rapids,
<br />7.8 miles downstream from the gage, or at the riffle at the
<br />mouth of Cathedral Wash, 2.7 miles downstream from the
<br />gage (fig. 1B). In 1983, the water surface between the
<br />Lees Ferry Gage and Badger Rapids was observed to be
<br />relatively smooth at a discharge of about 90.000 ft3/s. with
<br />the riffle at Cathedral Wash "washed out" (Kenton Grua,
<br />river guide, oral commun., 2002); this observation
<br />
<br />02245
<br />
<br />Phvsical Characteristics of the Lees Ferry Gaging Reach 13
<br />
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