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• DRAFr February 25, 1998 L Hydrology of the Green River Basin A. General Basin Description The hydrology of the 115,800 km2 Green River drainage is dependent on spring snowmelt from the Rocky Mountains of Wyoming, Colorado and Utah. The principal tributaries include the Blacks Fork, Yampa, White, Duchesne, Price, and San Rafael Rivers. Flow in the main stem Green River has been regulated by Flaming Gorge Dam near the Utah-Wyoming border since October 1962. Additional water storage facilities and diversion dams exist throughout the basin which have altered the seasonal hydrograph of the Green River as measured at the principal gaging stations at Jensen and Green River, Utah. These facilities include Fontenelle Reservoir on the Green River upstream of Flaming Gorge, Taylor Draw Dam and Avery Lake on the White River, Strawberry Reservoir and associated transmountain diversions on the Duchesne River, Yamcolo Reservoir, Stagecoach Reservoir, Catamount Lake, Steamboat Lake and Elkhead Reservoir on the Yampa River, and other small water resource facilities throughout the basin. The source areas of water and sediment in the Green River watershed are not distributed equally in the basins. The primary water source areas are located in the headwaters of the various is tributaries throughout the Rocky Mountains. These areas yield little sediment. On the other hand, sediment is delivered from the semi-arid regions in the middle to lower portions of the watershed as in the Little Snake Basin (Andrews, 1986). These regions contribute only a small fraction of the total flow in the Green River but a large proportion of sediment to the river (Iorns, Hembree and Oakland, 1965). B. Hydrologic and Geomorphic Setting of the Green River Several criteria can be used to describe the varying character of the Green River along its course. Changes in streamflow and basin geology are used in this chapter to organize research activities conducted to evaluate the geomorphic history and present condition of the Green River. Hydrologic Reach Description The Green River can be divided into three reaches, delimited by major tributaries. Reach 1, Green River upstream of Yampa River to Flaming Gorge Dam, is about 104 km in length. The hydrology of this reach is dominated by releases from Flaming Gorge Dam; streamflow is recorded at a gauge just below the dam. Reach 1 is straight to meandering and, with the exception of Browns Park, is tightly confined by the adjacent steep-walled canyon topography. Reach 2, Green River from the Yampa River to the White and Duchesne Rivers, is about 158 km in length. Streamflow in this reach is recorded at a gauge near Jensen, Utah, about 30 km downstream from the Yampa River. This is a relatively long meandering reach with numerous • sub-segments of varying geomorphic characteristics. It begins immediately downstream of the