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<br /> <br />A, <br /> <br />l&~- ,< <br />fliC ~ <br />'~.. <br /> <br />B. r <br /> <br />- <br /> <br />. -. <br /> <br />I <br /> <br />I <br /> <br />Figure 5. Flow over the gravel bar at the mouth of the Paria River at a range of discharges. (A) Downstream view in June 1915. The Colorado <br />River is flowing through the left-bank main channel and through two channels across the bar into the lower portion of the Paria River. <br />Estimated discharge of the Colorado River is 50,000 cubic feet per second, based on records from the Yuma gaging station. The location of the <br />Lonely Dell Ranch is indicated, where elevations of the high.water marks of the 1884 and 1921 floods were measured on June 7, 1922, Also <br />shown are the future locations of the road and levee in part 8. built by the National Park Service after regulation of flows by Glen Canyon Dam. <br />Source of photograph: HE Gregory photographs 297 and 298, Us. Geol09ical Survey Photographic Library, Denver. Colorado, (8) Same view <br />as in A on April 15, 1995. Discharge of the Colorado River is 9,500 cubic feet per second and flow is restricted to only the left-bank main <br />channel. Photograph taken by D,J. Topping of the U,S, Geological Survey, <br /> <br />suggests that the fIrst hydraulic control downstream from <br />Lees Feny at high stage is Badger Rapids, Evidence for <br />the Cathedral Wash riffle being the high-stage hydraulic <br />control is provided by the presence of high-elevation <br />tenaces that extend downstream from the Lower Staff <br />Gage (fIgs. IB and 4A), The fIrst high-elevation tenaces <br />occur on the right bank for about 700 feet downstream <br />from the Lower Staff Ga,.ge, then continuously on the left <br />bank for more than 0,6 rliiles, ami terminate just above the <br />riffle at Cathedral Wash, Although high-elevatiun tenaces <br />are present locally downstream, they are far less <br />continuous than those above Cathedral Wash. Flood <br />deposits preserved within the high-elevation tenaces <br /> <br />between the Lower Staff Gage and Cathedral Wash were <br />first studied by O'Connor and others (1994). They <br />detennined that the uppennost unit within these tenaces, <br />the "G I" deposit, was likely deposited during a historical <br />llood, which they speculated was the 1884 llood. [n <br />making this stratigraphic call, however, O'Connor and <br />others (1994) did not have access to the historical data <br />from the Lower Staff Gage. Extrapolation of the measured <br />water-surface profile during the peak of the 1921ll00d by <br />means of a best-fIt linear regression (fig. 4A) indicates that <br />the G I deposit was more likely fomled during the 1921 <br />flood than during the 1884 llood, <br /> <br />14 Computation and Analysis of the Instantaneous-Discharge Record for the Colorado River at Lees Ferry, Arizona-May 8. 1921, through September 30, 2000 <br />