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OD[l807 averages, from 12,500,000 A.F, annually, or about 75 per cent of normal, as during 1931 to 1940, to 20,- 000,000 A,F, annually during previous and more favorable ten-year cycles. It is therefore apparent that extensive regulatory storage capacity would be required to equalize the streamflows and regulate the original water produc- tion to its average of 16,600,000 A,F. annually, or so much thereof as may remain after natural convey- ance losses are deducted. Some of the required capac- ity, to command the production near the State's borders, may be ignored as it would be wholly with- out benefit to Colorado, From all additional reser- voirs, and from their greater exposed water sur- faces there would, unavoidably, be increased evapora- tion losses, Sites in Colorado, above the places of intended use, are not plentiful, and to comment that such a program would be expensive seems unneces- sary, In general, it may be said that complete equal- ization of Colorado's water resources through regula- tory reservoirs is neither feasible nor possible; and that physical and financial limitations prohibit the construction of storage works of sufficient capacity to prevent reservoir spills in years of maximum run- off and hence to provide carryover storage from wet to dry decades, Regulatory Reservoir The construction of regulatory reservoirs, to pro- vide carryover storage from one wet year to a fol- lowing dry year, has proven infeasible, in several instances, for physical or financial reasons, or both. In fact, in connection with many of the water proj- ects under investigation in Colorado, we find some difficulty in the promotion of reservoir developments that will provide regulation and carryover storage from winter months to the following summer season, and from the snow melt period in early summer to the chronically deficient late summer months of the same season. With these practical considerations in mind, and because the needs for supplemental water supplies are commonly greatest during years and cycles of drouth, when water production is least, our attention should be directed, not so much to long- time average values, but more largely to climatic cycles when production quantities are minimum, To illustrate the sub-normal conditions of record, we have selected the drouth year of 1934, and the drouth cycle of 1931 to 1940, which in Colorado com- monly represent near-minimum conditions, The fol- lowing table presents comparisons with long-time average values at several stream gaging stations. Minimum Annual Stream Flows In Relation to Long-Time Averages L"nl'-Tine Period 1~31-1940 Av~ral"e. Year 19M AVl'r...el 1000 1.001) Per 1.000 Per A,F.. A,F, Cent A,F, Cent 1900-1940 2,162 987 46 1,703 79 1895-1940 557 304 55 443 80 River Period Colorado (a) Arkansas (b) Cache Lll Poudre (e) 1895-1940 320 Green (d) 1895-1940 4,992 Colorado (el 1897-1940 14,381 Colorado (f) 1897-1940 16,199 Notes: . -Assume at 100 per cent, (3) At Glenwood Springs, Coloratlo, as recorded, (b) At Canon City, record corrected for by-passed and imported quantities, (e) At Canon .Mouth, record corrected for by-passed and imported quantities, (d) At Green River, Utah, as recorded, (e) At Lee Ferry, Arizona, recent years as recorded, earlier }"eaTS as calculated, (f) At Lee Ferry Arizona, estimated virgin flow, after allowances for assumed upstream deple- tions. 145 45 1,214 24 3,966 28 5,486 34 244 76 3,356 67 10,167 71 12,210 75 From the above and other streamflow and trans- mountain diversion records, it appears that runoff from high-mountain areas (more than half of which commonly occurs in periods of 4 to 8 weeks) may be expected to decline to 50 per cent of normal in a single drouth year, and to about 80 percent of normal during the average year of ten-year drouth cycles, On this basis the existing and contemplated trans- mountain diversions from the Colorado river system for use in eastern Colorado, estimated to average 2,000,000 A,F, annually may be expected to average 1,600,000 A,F, annually during ten-year drouth cy- cles, such as 1931-1940, and to decline to about 1,000,- 000 A,F, in a year of severest drouth conditions, such as 1934, unless carryover storage from wet to dry years be provided so as to increase the minimum year yields, Accompanying the below-average or sub-normal vields of trans-mountain diversion projects during drouth cycles, the demands for supplemental irriga- tion supplies at such times are above-average, Ab- normal demands for irrigation water result from concurrent deficiencies in local precipitation and water production, Furthermore, under such condi- tions, the lands and crops require greater and more frequent irrigations, for the reason that losses of soil moisture are increased because of the higher temperatures, increased wind movement, greater at- mospheric aridity, and above average rates of evap- oration that characterize the climatic conditions in Colorado during drouth cycles, .. U .balanced Relation With respect to the second problem, of an un- balanced relation between the water and land re- sources of the State, it may be noted that, over the 104,000 square miles of State area, the total produc- tion of 16,600,000 A.F. in an average year is at the rate of 160 A,F, per square mile of area, In this connection the extremes range from ,zero in a few closed basin areas, to runoffs of more than 2,000 A,F, per square mile in several small tribu tary valleys, Considered by major stream basins, the runoff rate is least, averaging but 23 A,F, per square mile in the. Kansas river basin in eastern Colorado, and is great- est in the North Platte basin where the average rate is 405 A,F, per square mile, Of direct application to the Colorado-Big Thomp- son and Blue-South Platte projects are the runoff rates of 84 A,F, per square mile in the South Platte river basin, and 338 A,F, per square mile in the Colo- rado river basin; and to the Gunnison-Arkansas proj- ect are the runoff rates of 41 A.F, per square mile in the Arkansas river basin, and 343 A,F, per square mile in the Gunnison river basin, Comparing all of western Colorado with the South Platte, Kansas and Arkansas river basins in eastern Colorado, the runoff rates are 293 A,F, per square mile on the West Slope, and 53 A,F, per square mile on the East, Expressed another way, western Colorado with 37 per cent of the land area has 68 per cent of the State's water resources, and eastern Colorado with 54 per cent of the land area has but 18 per cent of the water resources, Land areas and water resources of Colorado are distributed by stream basins as fol- lows: