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. f <! oj . ( I. .'. (: , I - 29 The Badger Wash vlatershed is located Smiles north"lest of Hack, Colorado, in an area very similar to parts of the Indian Wash drainage area. Measurements on is small 'reservoirs (installed by the Bureau of Land Management) 'in the Badger Wash Watershed showed an average annual sedimentation rate of 2.1 acre-feet per square mile. The period of record was five years. The old reservoir in which sediment was measured as a part of the investigations is located on the west fork of Indian Wash. The drainage area above this reservoir is' 1.75 square miles. The reservoir was constructed by the Civilian Conservation Corps and had been in operation ror 23 years at the time of the survey. A total accumulation of 34 acre-feet of sediment was measured, giving an annual rate of 0.85 acre-foot per square mile. Since this reservoir is now filled with sediment to within six inches of the top of the dam, it is assumed that considerable quantities of sediment have been carried past the dam during the period of record. The source of sediment produced by erosion in the Indian Wash drainage area above the proposed reservoir is estimated to be about equally divided between sheet and small qully erosion and channel cutting. Sheet and gully.erosion are highest on the bare shale slopes, which are present over a large part of the area. Channel cutting is most significant along the larger drainages, most of which are in the process of additional bank cutting through old floodplain areas. In computing future rates of sedi~entation at the proposed reservoir site, consideration was given to the amount of reduction in sedlluent production that will result fram proposed land treaL~ent measures to be installed in the watershed. It is estimated that these measures will reduce the capacity requtred for sediment storage at the proposed reservoir by 5 percent. Consideration was given to the fact that sane land treatment measures in this plan will become effective immediately after construction, while others will require several years fram the start of the project to became effective. The future rate of sedimentation at the proposed reservoir site with the project installed was determined as being 1.75 acre-feet annually per square mile of drainage area~ The capacity equivalent of sediment storage in the reservoir is 1.64 inches. The estimated sediment storage requirement at the reservoir for a fifty-year period is 570 acre-feet. In arriving at this figure, a sediment trap efficiency of 80 percent was assumed for the proposed structure.