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-, r-.:; --1 en w 38. The results of applying consolidation effects to the sediment deposits are shown in the last column of table 13 and were. used to construct the bar graph shown on plate 25. The estimated deposition from the suspended sediment load is considerably higher than the sedi- ment deposition calculated from the range line survey by the Constant Factor Method. The consolidation may be greater than computed due to the possibility of coarser grading of the reservoir deposits, or the 75.7 pounds per cubic foot weight used to compute the volume of sedi- ment inflow may be too low. These would indicate a larger volume of sediment inflow than is actually experienced. Further studies will be made on size distribution, density of the sediment beds, and unit weight of the inflow as data become available. I '.1. i 39. The change in reservoir capacities occurring between the resurveys of 1957 and 1962 was due to sediment deposition during that period and consolidation of existing deposits. The reservoir capacity', belOW elevation 3,820 increased throughout and all sediment deposition took place above that elevation. Between the resurveys of 1962 and 1966 the reservoir capacity was decreased throughout except for the segments between elevations 3,845 - 3,850, and 3,860 - 3,865. The tabulations present:ed in table 14 Iilustrate the changes in capacity that took place between the 1957, 1962, and 1966 resurveys at five- foot elevation intervals. Most of the sediment deposition between the 1962 and 1966 resurveys was between elevations 3,785 and 3,795 where 3,605 acre-feet deposited. The next highest amount of sediment dep- osition occurred between elevations 3,820 and 3,830 where 2,436 acre- feet deposited. 40. Trap effiaiena~ of John Martin Reservoir. The trap effi- ciency of John Martin Reservoir is highly variable and depends on operating procedures. Whenever water is stored in the reservoir, the trap efficiency is in excess of 90 percent. It approaches zero percent when riverflow is routed through the reservoir. In Water Year 1964 the measured suspended sediment outflow exceeded the inflow. This indicated erosion of previously deposited sediments. The average trap efficiency for the period of record, since beginning of operations (1943 through Water Year 1966) has been 88.8 percent as indicated in table 8. During the period of the latest resurvey, March 1962 to September 1966, the annual trap efficiency varied from zero in 1964 to 96 percent in 1966 with an average of 51.4 percent. The trap ef- ficiency is based on total inflow and outflow of sediment loads. SUMMARY AND CONCLUSIONS 41. Summar~. Results of the latest resurvey including the trends, conclusions, and recommendations are as follows. a. This is the eighth resurvey of the sediment ranges in John Martin Reservoir since the original survey of April 1942. Total reservoir depletion is 70,654 acre-feet or an average annual rate of 11