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2.3 Basin Characteristics <br />The White River is a tributary to the Green River, which is in turn a tributary to the Colorado <br />River. The White River joins the Green River downstream of the study reach in Utah. The <br />White River has its headwaters in the Flat Tops Wilderness to the east and south and in the White <br />River Plateau to the south and west. The watershed area at the downstream limit of the study <br />at the Utah stateline is 3552 square miles. The elevation within the watershed ranges from above <br />11,500 feet above Mean Sea Level at the headwaters to 5070 feet at the downstream limit of the <br />study. The average slope within the study reach is approximately 12 feet per mile with a <br />maximum of 20 feet per mile in the upper reach and a minimum of 8 feet per mile at the Utah <br />border. <br />The climate within the White River basin is classified as semi -arid and is characterized by low <br />precipitation, large daily temperature range, low humidity, and frequent wind. The primary <br />sources of moisture are from air masses originating in the Pacific Ocean from October through <br />April, and airmasses from the Gulf of Mexico during the late spring and summer. Normal annual <br />precipitation ranges from approximately 10 inches near Rangely to approximately 16 inches near <br />Meeker (18 miles upstream of Rio Blanco Lake). Most of the annual precipitation (60 percent) <br />occurs as snow from October to April. Rainfall can occur as convective -type thunderstorms <br />during the late spring and summer months generally over the lower elevations of the basin. The <br />White River basin, from its headwaters to the Utah stateline, is shown in Figure 3. <br />2.4 Summary of Drainage Areas <br />The drainage areas for selected hydrologic points were determined through planimetering. The <br />results of the planimetering were then compared to known drainage area values at USGS gage <br />locations and at published flood study locations. The drainage areas at these selected hydrologic <br />points are shown in Table 2. <br />u <br />1 5 <br />