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i....". I ", I I I I I i St~IMENT YIELDS IN THE YAMPA RIVER BASIN Source Areas of Sediment and Water ~requently, the sediment load of the stream is not suppl ied equally from all a,eas of the drainage basin. Some areas of a drainage basin contribute a relatively large part of the annual sediment load; whereas, other areas of the drainage basin contribute relatively minor quantities of sedim~nt. Sisi larly, runoff seldom is supplied evenly from throughout the dr~inage basin. Thus, scdimcnt- and ruroff-source areas ofte.n can be ideritJof"ied for a dr'sinage basin proxided the sediment loads and funoff are measured or esti- rlated at several points wit~in the drainage basin. The term.'.!!iource area'l is used in a relative se~seto-describe those pa~ts of.the drainage basin which supply a large percentag:=.,'9f theS'"edilnent load or runoff compared to thei r areal extent.. ;-;--- ~~--- The rean:~nnual sediment load and runoff at the gaging stations in the YanDa Riv~r basin are shown on figure 4 as a percentage of the total sediment and runoff or the Yampa River at Deerlodge Pa,k (fig. 1). A comparison of the values of the individual stat~ons shows that sediment and runoff are not contributed to the streams equally throughout the basin. Furthermore, the principal source areas of sediment and runoff are different. One of the most striking differences exists between values at sites On main-stem rivers draining the two major subbasins--the Little Snake River near Lily (site 1) and the Yampa River near Maybel I (site 17). Although the drainage areas contributing to these two gaging stations are about equal, 3,730 mi2 (9,660 km2) for the Little Snake River subbasin at site 1 versus 3,410 mi2 (8,830 km::) for the Yampa River subbasin at site 17, the respective sediment loads and runoff are markedly different. The Little Snake River subbasin suppl ies 27 percent of the annual rur.off to the Yampa River at Deerlodge Park but nearly 69 percent of the sediment load. Conversely, the Yampa River subbasin contributes 73 percent of the runoff and only 27 percent of the estimated total-sediment load for the entire Yampa River basin (fig. 4). Comparisons for other areas are equally striking. Most of the large /~sediment load of the Little Snake River subbasin enters the main-stem Little Sncke River betl'!een Dixon (site 8) and Lily (site 1) (Fig. 4). About 60 percent of the entire sediment load of the Yampa River at Deerlodge Park is contributed from the drainage area between the Little Snake River near Dixon and t~e Little Snake River near Lily oClging stations. Thus, the lOI-Jer part of the Little Snake River subbasin is the major sediment sourc~ area within the Yempa River basin. This area is less than 35 percent of the entire ~asin area and supplies less than 3 percent of the runoff. ~ f n c C:1 t r a s t, the e a s t ern par t 0 f the bas i n ups t rea m from 5 i t e 8 0 nth e Little Snake River and site 47 on the Yampa River supplied approximately 76 percent or the total basim'!ide runoff and only 14 percent of the sediment load, 14