7049 - Laserfiche WebLink

Home Browse Search

sediment yields are already relatively la~ge due to a lack of soil development and sparse ground cover. Thus, bec3use surface mining wi II not greatly alter these factors, the relative increase in sediment yield wi II be small. Furthermore, areas of surface mining in the \'Iestern part of the basin actually being disturbed are expected to be relatively small. Thus, the additional sediment load car'ried by the Yampa River at the /-I,aybe1l gaging station due to surface ~ining wil I be only an estimated 2 to 7 percent of the. present mean-annual sediment load passing that site, depending upon ,!:,he volume of coal production. Thus, even at the greatest pr6fected \'olume-~~t>f coal production in the ',basin by 1990, the add,itional quantity of sediment", contributed to the streams vJill b~ .s]TIall relative to- the to,tal quanf:i-tyof' sediment being tri1nsported out of ' the Yami2.a [Uver subbasin 0,0 the basin in its en t ; r e t y . , ,-",",_. ~.~~ SUMMARY The mean-annual sediment loads at 17o~aCJir)(J stations In the Yampa River basin of Colorado and Wyominq were computed by the flow-duration, sediment- transport-curve method (r1ilJer: 1951). - Sediment-transport cur'ves for each gaging station were constructed by combining separate curves for suspended- and bed!oad-sedi~ent discharges. The suspended-sediment curves were determined by fittina a mean r-elation bet\\leen measured suspended-sediment discharge and water discharge. The bedload-transport curves were derived from bedload-tr~nsport rates computed for various discharges by the Meyer- Peter and ,'1ue! ler (19lI8) reli1tion. The annual sediment loads \\lere computed by combining the total sediment-transport curve with the observed cumulative frequency of water discharges and summing the products. Average sediment yields for the contributing drainage areas upstream from the 17 gaging stations show that sediment is not contributed equally throughout the basin. The most significant sediment-source area I ies in the downstream part of the Little Snake River subbasin. This area supplies about 60 percent of the entire sediment load passin9 in the Yampa River at Deerlodge Park, although it is less than 35 percent of the total basin drainage area, and contributes less than 3 percent of the lotal runoff. In contrast, the eastern part of the bas[n contributes only 14 percent of the sediment load and 76 percent of the annual runoff. ,~ The distribution of sedi~ent yields in the Y2M2a River basin closely ':, reflects the variations in annual precipitation. The iargest sediment yields 1 are found in those parts of the basin which receive from 10 ~o 14 inches - \ (250 to 360 s;n) of precipi tation annually. This observation is in agreement ~ith the conclusion of Langbein and SChlU,llll (1958) that the greatest sedimert yields in the Uni~ed States occur from drainage areas having about 12 inches (305 mm) of annual precipitation. As the mean-annual precipitation increases above 12 inches, the sediment yield dccl'cases. Thus, as precipitation increases fro~ west to east across the Yampa River basin, sediment yields decrease. 30 ~~~:~?~t"i~~~~~,~~~:iZ~~\~;U::.i'x.'!*~~~~;~\,"i"#~~~ixa.wi:y..~Ji!!~~~~~~,"H~