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1060 where HDR = headgate diversion requirement, GCU = gross consumptive use, EP = effective precipitation, CL = canal losses, LL = lateral losses, and FL = farm losses. Table 7 shows the headgate diversion requirements for a full water supply for irrigation seasons 1949-70 based on an irrigated acreage of 6,000 acres. Values from 1949 to 1965 are from Bureau of Reclamation .!,omi>\i~ae,iqns. " Subsequent values are from computations made by Water Board staff members using the Same procedure as the Bureau so they will be comparable. Table 8 has been prepared utilizing headgate diversion data from Table 1 and computed requirements from Table 7. This table shows months when diversions were less than requirements during the 22-year period 1949-70. During the months of April, September and October when consumptive use is relatively low, the company-owned wells may have furnished enough water to alleviate short- ages in most instances. However, it would be difficult for these wells alone to make up the shortages that occur so frequently in July and August. It will be noted from Table 8 that 1954 and 1963 were the critical years in the 1949-70 period since there was some shortage in every month of the irrigation Season in those years. The total computed shortages were 9,500 ac-ft in 1954 and 11,200 ac-ft in 1963. Figure 3 is a histogram depicting graphically by months the relations between average headgate diversions, average headgate requirements, "realisticll headgate requirements and comparing these quantities with supplies that would be available to the ditch if both decrees were diverted all of the time. The term "realistic requirement" is used here to indicate a headgate requirement above the average and below the absolute maximum. On the assump- tion that no ditch can be guaranteed a full water supply 100% of the time and that any ditch can operate with something less than a full supply for short periods, the "realistic requirement" was computed as the upper quartile of values listed in Table 7. A requirement such as this is much more realistic than an average requirement in determining the adequacy of decrees or in ar- riving at volumetric limitations on the quantity of water needed by the ditch on either a monthly or a seasonal basis. It is evident from Figure 3 that on a seasonal basis, average historic diversions have been a little larger than the average seasonal requirements. For the months of April, May and June average diversions exceed average requirements, but for July, August, September and October the reverse has been true. Thus, a better regulated supply would help the situation. Historically, an additional supply has been provided by company-owned and shareholder-owned wells. It is also evident from Figure 3 that the 1867 decree for 13.4 cfs does not provide sufficient water to meet even average headgate requirements for April, the month when headgate requirements are lowest. On the other hand, the amount of 7,850 ac-ft per month available when both the 1867 and 1887 decrees are diverted provides 3,500 ac-ft more than the realistic requirement of 4,350 ac-ft - 20 -