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<br />':J <br />-.: l <br />N <br />-..J <br />Ul <br />.... <br /> <br />on the Arkansas River and tributaries. The report summarizes current <br />information on investigations being ~onducted which may be of interest <br />to the Subcommittee on Sedimentation, lnter.-Agency Committee on Water <br />Resources, It will serve as a history of the investigations which may <br />be of immediate and future interest to engineers concerned with sedi- <br />mentation investigations of other reservoir projects. <br /> <br />5. Saope. The sediment investigations program in the Arkansas <br />River subbasin in Colorado was origLnally planned as a comprehensive <br />program to supply sediment data for future project planning and es- <br />pecially fOI use in the planning of the operation and management of John <br />Martin Dam and Reservoir., Previous reports have included analyses of <br />the various aspects of and factors influencing sedimentation, along <br />with trends and conclusions which were considered pertinent, To avoid <br />repetition of data previously presented, this report includes primarily <br />only recent data and refers to previous reports for the earlier data <br />when necessary. This report includes information obtained from the <br />data collection program and presents trends and conclusions based on <br />all of the resurveys. <br /> <br />ARKANSAS RIVER SUBBASIN ABOVE GREAT BEND, KANSAS <br /> <br />6. Drainage area. TIle total. diainage area of the Arkansas River <br />subbasin above Great Bend, Kansas, is 33,986 square miles. The length <br />of the main stem is about 575 miles. Above John Martin Dam, the drain- <br />age area is 18,933 square miles and the length of the main stem is <br />about 290 miles, About 30 percent of the area above John Martin Dam <br />is mountainous and some peaks are over 14,000 feet above m,s.l. The <br />other 70 percent is plains generally between 6,000 and 3,800 feet <br />above m.s.l. Plate 1 shows the drainage area of the Arkansas River <br />above Great Bend, Kansas. <br /> <br />7. Sediment SOU1'aes. Most of the sediment transported by the <br />Arkansas River is derived from the areas below Pueblo, Colorado. From <br />records of sediment sampling,. it has been determined that the areas <br />above Pueblo produce only about 500 acre-feet of sediment annually and <br />that less than 25 percent of the 500 acre-feet reaches John ~lartin <br />Reservoir. The principal tributaries on the north side of the river <br />that produce sizable quantities of sediment are Fountain and Chico <br />Creeks near and below Pueblo, Colorado, which contribute about 1,200 <br />acre-feet annually to the main stem. The south side of the watershed <br />between Pueblo and John Martin Dam yields about 6,000 acre-feet of <br />sediment annually to the main stem. The principal sediment-producing <br />streams from the south are Huerfano, Apishapa, and Purgatoire RiVers. <br />The average annual amount of sediment computed to reach John Martin <br />Reservoir for the period October 1942 through September 1966 was <br />3,944 acre-feet. Of this amount, about 55 percent was contributed by <br />the Purgatoire River which enters the reservoir below Las Animas, <br />Colorado. <br /> <br />2 <br />