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. , , , ,* 2GZ,j Hydrology used early in the hydrology studies and differ slightly from figures used elsewhere that were developed later from land classification data. Updating the acreages used in the hydrology studies would not change the results significantly. The 23 major ditches in the potential service area have histori- cally diverted 346,300 acre-feet per year from the river and existing reservoirs. Of this amo~nt, l64,200 acre-feet became available at the farm. In addition, 86,900 acre-feet of ground water per year were pumped at the farm. The combined sources provided a supply of loW acre-feet per acre at the farm headgate. The average annual farm headgate requirement for supplemental water was found to be 71,500 acre-feet on the l34,600 productive acres of irrigable land histori- cally irrigated and 4l,700 acre-feet on the 19,600 productive acres of intermittently irrigated land. Table 12 is a summary of the historic water utilization. . The average annual shortage of l82,800 acre-feet as shown in table 12, does not give'an adequate description of the situation because of the wide fluctuations in annual requirements. For the period 1947, through 1961, river diversion requirements for project water would have ranged from about 87,000 acre-feet in 1951 to about 3l0,OOO acre-feet in 1955. Shortages are experienced every year, primarily because storage facilities are lacking on some of the ditch systems. WATER UTILIZATION A reservoir operation study was made to estimate the supple- mental water that could be realized from the storage of surplus flows and its subsequent release to meet the computed supplemental water requirements of the 23 major ditch systems in the Lower South Platte Water Conservancy District. Estimates of storable flow were based on actual flow conditions for the l5-year study period, 1947-1961. The study was based on a reservoir capacity of 430,000 acre-feet (355,000 acre-feet conservation capacity after 50 years of sediment encroachment plus 75,000 acre-feet of joint use capacity). All requirements for supplemental water were met as long as project water was available. Supplemental water was not provided class 6w lands. 64 .