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10,000 5000 3i 0 Z OJ OV 0 W W Q N 15,000 Wui ir a 10,000 ?w LL 5000 Q om 0 Z W Z 10,000 5000 -A - - 1951-62 - - ----1965-83 - r? =B = 90 Percentile = - ---- 50 Percentile Period of record 1951-62 _ - ------ 10 Percentile rj v? _ _ \ - _C 90 Percentile - ---- 50 Percentile - - -----10 Percentile Period of record 1965-83 - Nhf./r1N,r\hV.yL OCT NOV DEC JAN FEB MAR APR MAY JUNE JULY AUG SEPT Figure 17. Daily streamflow at site 34 (Green River near Greendale, Utah) before and after the initial filling of Flaming Gorge Reservoir. A, Mean daily streamflow. B, Daily streamflow for selected non-exceedance probabilities before initial filling. C, Daily streamflow for selected non-exceedance probabilities after initial filling. a 55-percent increase from the preintervention median load (table 4). The increase in dissolved-solids load may have been caused by several factors, including an increase in streamflow between the two periods and an increase in dissolved-solids loading upstream. At site 30, just upstream from Flaming Gorge Reservoir, median annual dissolved-solids loading in- creased by 118,000 tons at approximately the same time. Dissolution of minerals from the reservoir bank material is another potential source of increased dissolved-solids load. The net dissolved-solids load added from dissolution of bank material has been estimated to be 1.59 million tons during 1963-72, an annual average of 159,000 tons (Madison and Waddell, 1973; Bolke and Waddell, 1975). Because most of the increase was dissolved sulfate, the primary mineral involved was believed to be gypsum. The preintervention period was not evaluated for annual monotonic trends because of the short period of record. No statistically significant annual monotonic trends were indi- cated during the postintervention period. Middle Green Subregion The middle Green subregion includes the Yampa River basin and tributaries and all the tributaries to the Green River between Greendale, Utah, and the confluence with the White River. About 7,100 acre-ft/yr is exported from the Little Snake River through the Cheyenne Diversion to supply water to the city of Cheyenne, Wyo. (table 1). It is the only trans- basin export from the Colorado River basin in Wyoming. About 65,000 acres is irrigated upstream from Maybell, Colo., and about 21,000 acres is irrigated along the Little Snake River. Large deposits of coal are mined from Cretaceous deposits in the Yampa River basin. Surface mines are active along Trout Creek, Foidel Creek, Williams Fork, Wilson Creek, and along the southern side of the Yampa River between Steamboat Springs and Hayden, Colo. Much of the basin contains outcrops of the coal-bearing Mesaverde Group (Williams Fork and Iles Formations) and Mancos Shale. Coal-fired powerplants near Hayden and Craig, Colo., use about 13,000 acre-ft of water per year from the Yampa River. Steinaker Reservoir provides late-season irrigation water for about 15,000 acres around Vernal, Utah. About 175,000 acres is irrigated in the Duchesne River basin. Since 1969, Starvation Reservoir on the Strawberry River has pro- vided water for late-season irrigation near the town of Duchesne, Utah. In addition to the Strawberry River inflow, water from the Duchesne River is diverted into Starvation Reservoir. Moon Lake stores water for late-season irriga- tion of about 75,000 acres near the mouths of the Lake Fork and Uinta Rivers. The Strawberry and Duchesne Tunnels export water west to the Salt Lake City-Provo area in the Great Basin. Water for diversion through the Strawberry Tunnel has been supplied by Strawberry Reservoir since 1913. Some water from the upper Duchesne River basin is diverted into Strawberry Reservoir, and minimal water is 40 Characteristics and Trends of Streamflow and Dissolved Solids in the Colorado River Basin