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o~1999 water released into tributaries by ditches at thei r terminus should be made. When ditches use operational water in this fashion, accurate measurements of the water so used should be made. The only long term tributary records of discharge avai lable for tributaries below Pueblo are those on the Purgatoire River. Even here the records are not continuous, and correlations of the records at Highland Dam near Las Animas were required to estimate the Purgatoire River inflow into the Arkansas River proper. Based upon this approach, the average annual discharge for the 1925-1966 period was 91,100 acre- feet; the maximum was 395,150 in 1942, and the minimum was 12,700 acre- feet in 1964. A comparis~ of the Purgatoire River flows with other measured tributary inflow for concurrent periods of time revealed that this river contributes more water than any other tributary. Monthly and annual flows for the Arkansas River at Canon City and at the state line and for the Purgatoire River near Las Animas are given in Table Nos. 2, 3, and 4, respectively. An attempt was made to obtain a correlation between the runoff of the Purgatoire River near Las Animas and precipitation at Rocky Ford and Lamar by single mass diagrams. Comparison of the curves showed a general trend, but it was too general to be of any value in the studies. CANAL DIVERSIONS Canal diversions on a monthly basis were tabulated and computer- ized for the 1927-1966 period for all canals from Pueblo to the state line. Although the Bessemer Canal diverts above Pueblo, it was included in the analysis. A tabulation of these diversions is contained in the appendix, and a print of the Catl in Canal diversions is contained in Table No.5, as an example of the data developed for the other canals. Average annual diversions by the Catlin Canal were 80,600 acre-feet for the 40 year study period, contrasted to maximum diversions of 112,100 acre- feet in 1962 and minimum diversions of 38,100 acre-feet in 1954. These values pinpoint the need for a regulated supply, especially when winter diver- sions are taken into account. Winter diversions, i.e., November to March, inclusive, by the Catlin Canal averaged 20,440 acre-feet per year. The study period of 1927-1966 was selected because it covers COn- ditions on the river prior to and after the construction of John Martin Dam and Reservoir, as well as the period of heavy ground water pumping, - 16 -