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water under this contract or some alternate storage possibility will be worked out between the two reservoirs. The storage decrees held by Two Forks Reservoir will undoubtedly affect the water-storage operation in Chatfield under the 1975 priority. The magni- tude of this effect will largely depend upon the reservoir operation practices which are unknolVll at the present. For the purposes of r~is analysis inflows to Chatfield from Plum Creek alone were separately considered, these waters not being physically available for the Two Forks decrees. Limited by the availabili'ty of d~ta, the study extended over a period of 26 years from 1948 through 1973. The estimated volumes that can be stored under the 1975 priority at the Chatfield Dam annually shows a wide variation --between 214,000 acre-feet and 0 acre-feet from the watershed including that of Plum Creek with a median of 9,460 acre-feet. The storable volumes from the Plum Creek wat rshed alone range between 68,000 acre-feet and' 0' annuaily, with a median of 2,220 acre-feet. During this analysis, it became obvious that the effect of the prolonged drought period of the mid-50's distorts the results of a frequency analysis to such an extent that any conclusion drawn from it would be so much on the conservative side that it would be useless. To illustrate this the record shows no storable water for the period 1953 through 1957 and nOlle for 1964 and 1968. The frequencies belonging to the event that no water can be stored under the 1975 priority would be in once every 4 years which is clearly in conflict with 0 divertible amounts in 5 consecutive years. To determine the severity of the 1950's drought period, the water-supply index for the basin composed of runoff recorded on the South Platte and its major tributaries was analyzed for a 46-year period. This analysis shows that the low runoff recorded in the calendar year of 1954 has a return period of 65 to 330 years. The 5-year dry cycle extending over 1953 through 1957 has a return period between 100 and 500 years. This clearly indicates that the analysis of the 1975 priority is limited in its results to the region of the 50 percent probability range whereby 2200 acre-feet of storage may be anticipated once in every 2 years from the Plum Creek watershed alone.' ,A more significant result of the study, however, was the need that was pointed out for the detailed analysis of the drought period experienced during the 1950's. - 12 - M. W. BITTINGER AND ASSOCIATES, INC.