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<br />":::.'=:> <br /> <br />",::l <br /> <br />N <br />00 <br />l\) <br />Ut <br /> <br />23. Reservoir sediment range survey. Longitudinal profiles of the <br /> <br />reservoir are presented on plate 5. These were drawn using the average <br /> <br />bed elevation at each sediment range as indicated by the original survey <br /> <br />and the 1962, 1966. and 1972 surveys. The distance between ranges is <br /> <br />measured along the axis of the reservoir. Longitudinal profiles indicate <br /> <br />comparative changes as produced by sediment deposition at each range line. <br /> <br />Profiles of representative sediment ranges are shown on plates 6 through IS. <br /> <br />24. The volume of sediment deposited in John Martin Reservoir between <br /> <br />the 1942 and 1972 survey was 80,449 acre-feet and the average annual deposi- <br /> <br />tion for the 30.0 year period was 2,682 acre-feet. The net increase in <br /> <br />deposition for the 5.6 year period from September 1966 to Harch 1972 was <br /> <br />9.795 acre-feet. <br /> <br />25. Special surveys at AT&SF Railway bridge. A railroad bridge <br /> <br />crosses the Purgatoire River in the upper reaches. of John Martin Reservoir <br /> <br />at Sediment Range 22. The bottom of the steel girder of the bridge is at <br /> <br />elevation 3,874.1, which is 4.1 feet above the maximum water surface eleva- <br /> <br />tion of 3,870. The lowest point in the. channel under the bridge, as shown <br /> <br />on plate 16, was originally 10.5 feet below the maximum water surface. The <br /> <br />opening between abutments, exclusive of the bridge piers, was originally <br /> <br />about 8,000 square feet. <br /> <br />26. . Although the pool created by John Martin Reservoir has never been <br /> <br />closer to the bridge than about 1 mile downstream, resurveys at the bridge <br /> <br />and at sections above and below the bridge have been conducted frequently <br /> <br />11 <br />