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<br />f\) <br />a <br />c:' <br />,.,.. <br /> <br />History and Effects of Water-Resources Development <br /> <br />Development of water resources for irrigation in the Upper Colorado River <br />Basin began with the earliest non-Indian settlement. The first diversion for <br />irrigation was begun in 1854 along the Blacks Fork near Fort Bridger, Wyo. <br />(Wooley, 1930). The first cooperative effort to supply water to a large area <br />was begun in i883 in the Grand Valley, near Grand Junction, Colo. (Follansbee, <br />1929). Irrigation development accelerated following passage of the Reclama- <br />tion Act of 1902, which provided Federal funds for storage and conveyance <br />facilities. Approximately 800,000 acres were being irrigated in the Upper <br />Colorado River Basin by 1905 and nearly 1.4 million acres by 1920 (U.S. <br />Department of the Interior, 1985). Since then, irrigated area has remained <br />relatively constant between 1.4 and 1.6 million acres. Consumptive use by <br />agriculture during 1940-80 averaged 2,18 million acre-feet annually, which was <br />approximately 21 percent of the mean annual streamflow at Lees Ferry, Ariz., <br />during the same period (U,S. Bureau of Reclamation, written cornmun., 1985). <br /> <br />Irrigated agriculture is the largest anthropogenic source of dissolved- <br />solids loading in the Upper Colorado River Basin. Drainage water from <br />irrigated land dissolves mineral salts from soil and aquifer material and <br />returns to the stream system with a greater dissolved-solids load than was <br />originally diverted. This process is called "salt pickup." Iorns and others <br />(1965) estimated the long-term average contribution of dissolved-solids from <br />irrigated land would be approximately 40 percent of the annual dissolved- <br />solids discharge from the Upper Colorado River Basin at the level of develop- <br />ment that existed in 1957. <br /> <br />Transbasin diversion of water from the Upper Colorado River Basin also <br />began early in the settlement period, In 1892, the Grand River Ditch began <br />diverting water from the Colorado River headwaters to the Platte River basin. <br />By water year 1920, 120,000 acre-feet were being diverted annually to the <br />Platte River, Arkansas River, and Rio Grande basins in Colorado and New <br />Mexico, and to the Great Basin in Utah. Diversions increased substantially <br />between water years 1950 and 1980 to about 800,000 acre-feet per year. During <br />water years 1973-82, diversions averaged approximately 5 percent of the <br />natural streamflow at Lees Ferry, Ariz. (Liebermann and others, 1988). <br />Transbasin diversions remove dissolved solids as well as water; however, <br />because most diversions occur in headwater areas where dissolved-solids <br />concentrations are small, the decrease in dissolved-solids discharge is small <br />compared to the decrease in streamflow in the basin. <br /> <br />Construction of large reservoirs lagged substantially behind development . <br />of irrigation and transbasin diversion facilities in the Upper Colorado River <br />Basin, The fi.rst reservoir that had a capacity greater than 100,000 acre-feet <br />was Strawberry Reservoir, completed in 1912 on the Duchesne River in Utah. <br />Total storage capacity in the Upper Colorado River Basin increased to 2.5 <br />million acre-feet by 1962. Then, during 1962-65, four major reservoirs of the <br />U.S. Bureau of Reclamation's Colorado River Storage Project were completed <br />(Navajo Reservoir in New Mexico and Colorado, Flaming Gorge Reservoir in Utah <br />and Wyoming, Lake Powell in Arizona and Utah, and Blue Mesa Reservoir in <br />Colorado), and storage capacity was increased to almost 37 million acre-feet. <br />This was more than three times the mean annual streamflow at Lees Ferry, Ariz. <br /> <br />5 <br /> <br />