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'. . e Review and Adiustment of the 1970-1977 Estimates The 1970's are an important historical hydrologic period due to several drought years during the decade. Drought occurred during 1974 and during an extended period of 1976-1 B78. In all likelihood, similar droughts could occur in the future, therefore, the 1970's were included in this study. Based upon a review of the 1970-1979 data, the estimated values appeared unusually high when compared to pumping from 1980 to present. For example, in 1977, the average annual precipitation in the basin was about 11.1 inches and estimated well pumping was 152,36!5 acre-feet. In similar precipitation years of 1988 and 1991, (11.1 and 11.6 inches, respectively) thE! estimated well pumping was 73,330 and 94,444 acre-feet, respectively, which are considerably lower amounts. In 1974 and 1975, the average annual precipitation in the basin was about 8.3 and 8.2 inches, respectively and estimated well pumping was 172,808 and 169,212 acre-feet, respectively. In similar precipitation years of 1981 and 1989, (7.9 and 8.8 inches, respectively) the estimated well pumping was 154,764 and 103,359 acre-feet, respectively. The unusually high pumping experienced during 1970-1979 can be attributed to several factors including: 1. The Fry-Ark Project was not being fully utilized. 2. The administration of wells was limited. 3. It may have been cheaper to operate a well than purchasing Fry-Ark water. 4. The winter storage program was not in operation during the early part of the 1970-1979 period. Measured and Estimated Pumpinq Amounts For Rule 3 wells in this study, two estimates of pumping were utilized. The first estimate used the initial estimates of pumping without adjustment. The second estimate used pumping estimates in which the 1970-1977 period estimates were decreased. That estimate was based upon the opinion that the 1970-1977 period was not reflective of a future drought period. Based upon a review of Fry-Ark Project releases to irrigators, Pueblo Reservoir storage contents, and precipitation records, the initial estimates for pumping during the period 1970-1977 are probably about 25 percent too high. The estimate for 1978, a critical dry year in the 1970's drought period, is approximately the same as 1981, a similar dry year. The estimate for 1978 is, therefore, representative. In Table III.A-5, the annual pumping for both estimates ;s presented. This table represents pumping estimates for all HI Model wells based on the Kansas vs. Colorado study. In Table III.A-6, CWPDA: Sec III.A 10/12/99 Page 7