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<br />'---~ <br /> <br />l\:i <br />~ <br />,""J <br />~I <br /> <br />45. The most recent profile shows less slope of the sediment beds <br /> <br />between the dam and range 8B, a distance of about 9.5 miles. This change <br /> <br />of slope with the growth of phreatophytes above ran~e 7 will induce <br /> <br />I <br />sediment deposition in the upper reaches of the reservoir; however, the <br /> <br />deposi tion in the vicinity of the conf! uence of the Purp,atoi re and <br /> <br />Arkansas River has been negligible. The thalweg elevation of range 16 <br /> <br />just below the confluence was slightly in excess of 3,850 feet on the 1%6 <br /> <br />range profile and this elevation has rarely been exceeded by the reservoir <br /> <br />water surface elevation. With operation of the reservoir at much lower <br /> <br />elevations than the 3,850 feet, which is normal oper"tlon, the tendency <br /> <br />of flows is to cut a well defined channel. <br /> <br />46. The channel opening at the AT&SF Railway bridge over the <br /> <br />Purgatoire River decreased 445 square feet since October 1966 for a total <br /> <br />decrease of 1,202 square feet since the original survey in January 1942. <br /> <br />The sections shown on plate 16 indicate the establishment of banks and a <br /> <br />clearly defined channel between stations 3+50 and 4+50. The pattern is <br /> <br />one of a deep, narrow channel during high flows and a wide, shallow channel <br /> <br />during periods of low flows-. This i:;; normal for channels in alluvial <br /> <br />materials. The high elevation of banks and channel precludes sediment <br /> <br />deposition at this location by backwater effects of John Martin Reservoir. <br /> <br />47. As pointed out on previous occas ions the computation of voltD1les <br /> <br />by the Constant Factor Method introduces an error. In August of 1968 an <br /> <br />aerial topographic map of the reservoir was made to elevation 3,855 feet. <br /> <br />Vata used in the original Constant Factor computations were from the <br /> <br />21 <br />