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,. , (f - , ::;., DescnptlOn of Basin The Colorado Ri\er Basin is relatively arid Compared to others. such as the Columbia River Basin ....hich drains apprO:l:lmately the same area. it carries a much smaller flow. Table 1 shows that \lohile the Colorado River Basin is one of the major drainage basins in the cominenral Umted States. its runoff is about equal to that of the Delaware River. 1,1,hich drams a much smaller area. Table 1.-Companson 01 nver baSin drainage and runoff River BaSin Area Runoff Runolf (square miles) (mIllion acre. feet per year) (IncheS per year) 244,000 15 " 1.234.000 ""0 6.7 258.000 180 13.1 12.000 14 20.9 Colorado MISSISSippi Columbia Delaware The Oows at various points in (he Colorado River Basin for the 19.U*97 period are gi\"en in appenJi, A. The records of now depict Wide fluctuations from month to month and consIderable variations from year (0 year. RESERVOIR STORAGE Wet and dry cycles haw pla~ed a significant role in bringing about the de\'e1opmem oflhe Colorado River resen.olr complex (figure 1). HIstoric records show that the annual flow of the river has vaned from less than 6 maf 10 more than :!O maf per }ear. The resen'oir system allows sufficient storage water to maintain the nows of the river to meet downstream needs during dry penods_ In additlon to the major resen'oir!i. numerous smaller resenom.. have been built on many of the trlbutanes. \1ajor storage began with Lake \kad in 1935 and concluded with the tilling of Lake Powell in 1980. The Colorado River Basin resen'oirs now have a combined slorage capacity equal to apprmimately four times the IOta I Jverage annual naturallundepJeted and unregulated) Ilow of the Colorado Ri\er. The flo" of the San Juan River is controlled by Savajo Dam. the Green River by Fomenelle and Flaming Gorge Dams. and the Gunnison River by the Wayne:'o:. Aspinall Unit Dams. Glen Canyon Dam is the only major dam on the maioslem of the Colorado River abO\:e Lee Ferry. but it comrols almost all the flow leaving the Upper Colorado Ri\'t~r Basin. Lake \1ead. fanned by Hoo\er Dam. supplies mosl of the storage and regulatlon in the Lower Colorado River Basin Lake \1eJd provides water for ungation. \1&1 uses. rower generation. tl('\lxJ control. recreation. and mJny other beneficial uses 7