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<br />.-:-.:J <br /> <br />27. Thirty-one readings were taken at sixteen locations in the <br />reservoir with a radioisotope density probe. The densities obtained <br />by this method, and those obtained from the eleven sediment samples <br />analyzed in the Southwestern Division Laboratory, are shown in table 10. <br /> <br />t-.J <br />--.] <br />en <br />Q <br /> <br />28. Degradation range survey. The flood of June 1965 destroyed <br />or covered 12 degradation range monuments. These monuments were re- <br />placed before the 1966 resurvey was made, Table 11 is a summation <br />of the aggradation and degradation from John Martin Reservoir to <br />Lamar, Colorado, a distance of approximately 23 miles. Location of <br />the degradation ranges is shown on plate 17 and profiles of the ranges <br />are shown on plates 18, 19, and 20. Graphic results of the degrada- <br />tion surveys are presented on plate 21. <br /> <br />29. The annual rate of degradation since the original survey <br />of January 1944 is less than 0.01 foot per. foot. The total average <br />degradation of the reach is 0.22 foot per foot. The summary of degra- <br />dation is shown on plate 22. <br /> <br />30. FZood of 1965. Sediment inflow to John Martin Reservoir for <br />Water Year 1965 was 14,729 acre-feet. Sediment outflow for the same <br />period was 665 acre-feet as measured at the gaging station on the <br />Arkansas River below John Martin Dam" The measured suspended sedi- <br />ment inflow at the Las Animas gage on the Purgatoire River was 7,936 <br />acre-feet. On the Arkansas River at Las Animas, the sediment inflow <br />was measured at 6,096 acre-feet. The drainage area of 643 square <br />miles between these gages and the dam contributed 697 acre~feet of <br />sediment. During the period 1 October 1964 to 16 June 1965 sediment <br />inflow to the reservoir was 886 acre-feet from the entire drainage <br />area. For the two-week period from 16 June to 30 June, sediment inflow <br />was computed to be 7,678 acre-feet. This amount of sediment is at- <br />tributable to the flood which occurred 18-19 June. Sediment inflow <br />for July, August, and September was 6,165 acre-feet. This indicates <br />a sediment inflow of 13,843 acre-feet in the 3-f/2-month period from <br />16 June to 30 September 1965. The computed inflow of sediment by <br />suspended sediment sampling and estimated intervening drainage area <br />for the 4.5-year period between resurveys was 18,507 acre-feet. <br /> <br />31. Density flow dQta~ During July, August, and September 1966, <br />the Resident Engineer at John. Martin Reservoir observed heavily <br />sediment-laden inflows on several occasions. These inflows,with a <br />greater density, would submerge under the clear surface water near <br />the head of the reservoir. Debris, carried by the inflow, was left <br />on the surface. A considerable increase in the suspended sediment <br />load carried in releases from the dam could be seen within 36 to 48 <br />hours after heavily laden inflows were noted. These flows traveled <br />between 9 to 10 miles during that time and the average velocity was <br />0.3 to 0.4 feet per second. Samples of these flows were not taken in <br />the reservoir but daily samples were taken as flows passed through <br />the outlet works. <br /> <br />8 <br />