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PRESENT AND POTENTIAL SEDIMENT YIELDS IN T~E YAMPA R!VER BASIN COLORADO AND WY0KlNG .~~ 8'f~Edmund D. And reI-IS ~~~.~ P.BSTRACT Average annual suspended- and total-sediment loads in streamflow were determined by the flow-duration sediment-trar.spor:-curve method at 18 sites in the Yampa River basin, Colorado and Wyoming. These computations indicate that about 2.0 mi 11 ion tons (1.8 mi llion metric tons) of sediment are carried by the Yampa River at Deerlodge Park during an average year. Significant areal differences in the sediment yield from various parts of the basin also were determined. The lower Little Snake River subbasin contributes about 60 ~ ercer.t of the total basin sediment yield, although it represents less than 35 percent of the area and suppl ies less than 3 percent of the streamflo'.'1. In contrast, the upland (easu-n) one-third of the bcsin [contributes only about 1~ percent of the sedi~ent yield but 76 percent of the 5 t reamf 1 O\-J. Projected economic development of the basin, es~ecially surface mining of coal, vlill impact the physical environr.\ent. Cepending upon the anount of coal mined, as well as the extent and location of land distur~ed, an estimated 10,000 to 30,000 tons per year (9,000 to 27,000 metric tons oer year) of additional sediment will be contributed to the main-ste~ Ya~pa River. The impact of this addi tional sedi~ent load wi 11 depend ~p~n where [I'iithin the basin it enters the stream channel. fj,]though the increased \sedi~ent load due to surface mining represents apJroxinately 2 percen: of :he \present total-sediment load, it could incre.ase ::he sediment load of the up?er Ireaches of the Yampa River by as much as 30 per-ceil. I f'ITRODUCT ION Development of coal resources of the YamQa River basin in northwestern Colorado and south-central Wyo~ing wi 1 1 have sigriflcant effects u~on :ne environment and natural rescurces of the :asin. The Yampa River Basin Assessment (Steele and others, 1976a, 1976b) was designed to describe the avai labi1 ity and qual ity of the basin's water reso~rces and to eval~a:e ::he potential envir'onmental and selected socioecono:-lic impacts of alt2ri'a:::v2 coal-resource development plans. T~e stLdy of sediment yields is on~ o~ several investigations comprising the overall basin assessment.