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UiHJ226 -45- I' " The above statements and other well-known enGineering facts are the basis for the statement that the irrigati on of large areas of lend on the headwaters of our streams builds up silently large underground reservoirs which equalize through seepage or return water the flow of our streams which ordinarily discharge 70 per cent of their e.nnual flow in the months of April. May. June, and July, J' The beneticial effect of return waters fror. irrigaticn of the 450.000 acres now irrigated in Hestern Colorado is partly masked by the building up of underground reservoirs on lands. but recently irri- gated and partly through diversion and reuse on new lands, Ten to fl,:fteen years may elapse before the full benefit of such return waters is evident in t he lower Yampa, White. Grand. Dolores. and San Juan Rivers. With 2.000.000 acres ultimately irrigated in Western Colorado and additional large areas in utah. New Moxico. and Wyoming. the benefits to the lower Colorado River from return water will not only be visiblQ.. but should be quite marked, The lower States of Ariaona and Cali fornia want the peaks knocked off the floods and better equalized winter flow. both for power and irrigation. Irrigation on the headwaters in time, will. therefore. autome.tica11y better conditions on the Lower Colorado. G:::;NERAL DATA COLORADO RIVER BASIN Amount Upper Basin Lower Basin Area Square Miles 244.000 - - - - - - - - Yearly unused run-off, 22 year s (at Yuma. Arizona, below Gils River) A.F. i7,000,000 - - - - - - - - Area Irrigated in 1916 (Hhistler) Acres 1.903.400 1.101,900 801.500 0, Undeveloped irrigable area 3.315.000 1,257,000 2,058,000 Total Irrigab1e Area 5.218.000 2.358 .000 2,859.500 Per Cent 45 55