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. W. G. Wilkinson, Water Commissioner for District No.3, has So, ?i,fI. determined the surplus flow from 1947 to 1960 from the daily ,9P.er-~ J+~7;"hl ) ations on the river and consideration of downstream riabts. ~ese r J, flows, averaging 24,500 acre-feet per year are presented in Table 2 and represent flows storable under a new storage right. 19 Historic vs Future Conditions A base condition for measuring the effects of the Cache la Poudre Unit was developed by considering significant changes in the historic water supply and use that may be expected to occur in the future without construction of the unit. . The "future without" situation for the Poudre Basin was assumed to comprise the presently irrigated lands and presently developed irrigation facilities with the effects of a considerably expanded municipal and industrial use of' present water supplies (discussed elsewhere in this report). No developments are foreseen which wouJ.d alter the Mountain Supply from historic conditions. Historic trans!llountain imports were assumed indicative of future conditions. I'resent ground water development and use were considered representa- tive of the future conditions. Since CBT deliveries to the Poudre Basin began in 1953, an average of 105,500 acre-feet per year has been d.elivered for use in the 'basin, with a maximum of 155,700 acre- feet in 1954. Based on studies prepared by the Region 7 Hydrology Branch, "Colorado-Big Thompson Project unused carriage capacity," May 1961, it was estimated that CBT deliveries to the poudre wouJ.d have averaged 117,500 acre-feet per year during the 1947-1960 period, had that project been in full operation throughout the study period (See notation on Table 4). The estimated future CBT deJ.iveries were considered in developing the base condition. Basin outflow will also be influenced to a degree by the CBT Project. It has been estimated that 10.3 percent of the CBT deliveries to the Poudre wouJ.d escape the Poudre basin as return flow. y Basin Depletion Studr An analysis of historic water supply and depletions of thie supply within the Poudre Basin is presented in Table 3. The first step in the a.ne.1ysis was estimating a net annual water supply, column (6), which included the mountain supply, precipitation over the irrigated area and CBT deliveries, less the annual change in content of the plains reservoirs. Basin outflow, column (9), was determined . Y CBT Definite Plan Report, Appendix I, Chapter 2, Page 298.