Hydrologic reconnaissance of the Green River in Utah and Colorado

The Green River, rising in Wyoming and draining high mountains in that state, northeast Utah and northwest Colorado, is a major tributary of the Colorado River. In the late summer, after the snow has melted from these mountains, the flow in the Green River reaches its minimum for the year. At that time a large proportion of the water in the river is returned to the atmosphere by evaporation and transpiration.

During a 21-day period in September 1948, when the flow was least for the year, the average flow of the river as it entered Utah from Wyoming was 515 cfs. In the 437 miles of its course through Utah and Colorado evapotranspiration losses averaged 430 cfs. The average discharge of the Green River into the Colorado was about 975 cfs. Contributions to the river in Utah and Colorado totalled 890 cfsi including 560 from tributaries. The calculated ground-water inflow was about 330 cfs, of which about 75 percent was contributed within the Uinta Basin. Verv little ground water was contributed to the river in the lower 180 miles of its course, where the river flows through canyon lands of the Colorado Plateaus.

These estimates are based upon information collected during a boat reconnaissance in September 1948, and upon data available from stream-gaging stations along the Green River and many of its tributaries. From these data an accounting was made of the water--as to both quantity and quality--in several segments of the river. For each segment determinations were made of the surface outflow, loss by evapotranspiration, and surface- and ground-water inflow. During the reconnaissance information was also obtained as to the relation of stream flow to regional geology and ground-water hydrology.

No detailed hydrologic studies have yet been made within the drainage basin of the Green River. On the basis of this recomiaissance, detailed studies in the Uinta Basin, Browns Park, and Echo Park areas are recommended as highly desirable, because of the possible relations of ground-water hydrology to river-basin development projects. Similar reconnaissance can be of value in delineating the areas where detailed hydrologic studies would be most fruitful throughout the upper Colorado River basin.