WSP04833 - Laserfiche WebLink

Home Browse Search

..... -..:I ..t:.. >A. ck!/OVl · · ~JWJ,t~W" return flows can cause a marked increase in the salt load in lat: t~er and autumn. The long-term annual mean conditions of the Colorado River as it exits the Upper Basin is 10.7 Maf (14,700 cfs), 7.8 Mtons of dissolved solids, and 540 mg/l. ,'J; .r The region was not settled until the mid-nineteenth century. Although water was used almost immediately for irrigation, stock ponds, mining, and water supply, the magnitude of the early use was small. Grand Ditch, the first transbasin diversion, was completed in 1896; Strawberry Reservoir, the first reservoir with a capacity greater than 10,000 acre-feet, was completed in 1912. Irrigated acreage increased from 1,070,000 acre-feet in 1910 to 1,480,000 acre-feet in 1930, but has not increased significantly since then. Transbasin diversions have increased from 90,000 acre-feet in 1920 to 210,000 in 1950 to 640,000 in 1980. Reservoir capacity increased from 350,000 in 1920 to 1,600,000 in 1950. In the 1960's, as a result of the Colorado River Storage Project, Lake Powell, Flaming Gorge, Navajo Lake, and the Wayne N. Aspinall Unit (Blue Mesa Reservoir and others) were constructed, increasing the current total capacity to 37.5 Maf. The capacity of Lake Powell alone equals 2-1/2 years of normal flow (Figure 1). For this study, dissolved-solids records were evaluated for 68 water-quality stations having either long periods of data collection or a strategic location (Table 1). The Upper Colorado River Basin may be divided into four main reaches, or divisions. The Colorado River above the confluence of the Green River is known as the Grand division. Major tributaries are the Eagle, Roaring Fork, Gunnison, and Dolores Rivers. Though it comprises only one fourth of the area of the basin, it contributes 47 percent of the basin's total flow and 51 percent of the total dissolved-solids load, with a mean concentration of 590 mg/l (Table 2). Major natural sources of dissolved-solids are the Glenwood Springs area and the Dolores River, which together contribute 17 percent of the total sodium and 38 percent of the total chloride. Another major source area is the gypsiferous Mancos shale region of the lower Gunnison and Uncompahgre Rivers and Grand Valley. This area contributes 24 percent of the total load of the entire basin and 34 percent of the total sulfate. The shale underlies irrigated farmland, and it is estimated by the Bureau of Reclamation that 2/3 of the salt load there is the result of irrigation return flow, which infiltrates and passes through the highly saline formation before returning to the river. The Green division comprises the entire Green River drainage basin. Major tributaries are the New Fork, Blacks Fork, Yampa, and White Rivers. Other tributaries, which drain substantial areas but do not contribute greatly to streamflow or load are the Big Sandy, Bitter Creek, Henrys Fork, Duchesne, Price and San Rafael Rivers. Though the Green division occupies nearly 1/2 the total area of the basin, it contributes only 38 percent of the total stream flow and 32 percent of the total salt load, with a mean concentration of 444 mg/l. ,J.. "<(,-,.,, it, . ,i;-l.,-.k.,/~' , .~ ,t.'.j -~i<i'