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D, 0.0010 E, 0.0010 . NOVEMBER 1 THROUGH FLOOD PEAK . NOVEMBER 1 THROUGH FLOOD PEAK UJ 0 FLOOD PEAK THROUGH OCTOBER 31 0 FLOOD PEAK THROUGH OCTOBER 31 C!J UJ '" C!J '" 0.0008 '" 0.0008 >- C!J UJa: UJ>- n.a: /<J\ n.a: OUJ Oa: ~~ ~UJ "'", "'~ UJUJ 0.0006 UJ", 0.0006 OUJ OUJ "'~ "'UJ 1{:2 ~~ a:0 =>UJ A1::w;y \ ii>- '?C!J 0.0004 'UJ 0.0004 a:", a:", i"C!J UJ", "''' :;:'" 5a: ~:Cb ~ . 5UJ UJ ~ . al al " 0.0002 oo09J I '" 0.0002 / => 0 z 1921 FLOOD 1921 FLOOD 0.0000 0.0000 5 10 15 20 25 30 5 10 15 20 25 30 STAGE AT LEES FERRY GAGE, IN FEET STAGE AT LEES FERRY GAGE, IN FEET Figure 6-Continued. Water-surface slopes as a function of stage: (0) In the reach between the Number 4 Gage and the Lees Ferry Gage, determined from 209 stage measurements made at the 2 gages between August 14, 1921, and September 22, 1923. Peak stage during the June 1921 flood althe Number 4 Gage was determined by analysis of the photographs taken by R,C, Rice in September--Gctober 1921 (figs, 81 and 831, (E) In the reach between the Cable Gage (490 feet upstream from the Number 4 Gage) and the lees Ferry Gage, determined from 3.196 stage measurements made at the 2 gages between April 26, 1924, and July 30, 1962 Peak stage during the June 1921 flood althe Cable Gage was determined by analysis of the photographs taken by R,C. Rice in September-October 1921 and WE, Dickinson in May 1924 (figs, 81 and 851, The bed generally scoured between Aptil and the third week in June each year, and filled between the third week in June and the end of October (Topping and others, 2000, fig. 6E). At stages less than about 15 ft (the stage of the reversal of curvature in the stage-discbarge rating curve), the water-surface slope in the reach upstream from the gage was about a factor of two steeper during the months when the bed was scouring than it was during the months when the bed was filling. Above a stage of about 15 ft, the water-surface slopes during the rising and receding limbs of the annual snowmelt flood were approximately the same in the reach upstream from the gage, COLORADO RIVER FLOODS AT LEES FERRY It is important to detennine accurately the magnitudes of the largest floods in the recent history of the Lees Ferry gaging station because these floods may have had a large role in detennining the present morphology of the Colorado River, and because these floods are an essential component of the natural hydrology of the pre-dam Colorado River. Although the magnitudes of floods after August 1921 were measured from existing cableways, the magnitudes of earlier floods can only be estimated from direct or indirect measurements of flood stage and estimates of the discharges at these stages, There is no way to detennine the maximum stage of every annual flood before August 1921, but it is possible to estimate the discharges of the two largest floods during the 37 years prior to installation of the cableway because both floods were observed. A flood whose stage was higher than any in subsequent years occun'ed in June 192], I month after the first staff gage was installed and 2 months prior to the installation of the cableway. An even higher-discharge flood in 1884 was witnessed by Jerry Johnson, the ferry operator, and his family, The date of the peak of the 1884 flood at Lees Ferry has been reported to have been either June 18 (Reilly, 1999) or July 7 (LaRue, 1925; Patterson and Somers, 1966). Because the peak of this flood was observed at the Yuma gaging station (660 miles 02243 Colorado River Floods at lees Ferry 17