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7 ~ Biq Thompson River to Cache la Poudre River , Major ditches diverting water in this section of the South Platte River include the Lower Latham, Patterson, and Plumb (Highland) Ditches. The sum of diversions of direct-flow water by these three ditches also shows a pronounced increasing trend over the years. These ditches ap- pear to be diverting some 40- to 45,000 acre-feet more river water per year now than during comparable periods in the past. Again, the major reason for this is probably the increased availability of river water in the lower portion of Water District 2 caused by increased return flows from the tributary areas to the west. . . Comparison of Inflows and Outflows Measured inflows to Water District 2 used in these analyses were the combination of flows at the (a) South Platte River at Henderson, (b) St. Vrain Creek at mouth near Plattevil1e, (c) Big Thompson River at mouth near LaSalle, (d) Cache la Poudre River at mouth near Greeley, and (3) COlorado-Big Thompson Project water via Sand Creek Reservoir. v The outflow from Water District 2 is measured near Kersey. Cor- relation and regression analyses and double-mass curves were used for the study of interrelationships and their changes over the years. The com- parisons were both on a monthly and a water year basis. The general findings are summarized below followed by some results in mathematical expressions. ~ 1. During the period of analysis (water years 1936 through 1966) on a yearly basis the outflow diminished as compared to the inflows very slightly from 1950 to 1956 relative to the period of 1936 to 1950. Since 1956 there has been a slightly greater outflow compared to inflows than the long-term relationship. However, the changes are so minor they can- not be considered significant on an annual basis. Looking at the analyses of the. monthly runoff figures, a diminishing outflow compared to inflow (or increased consumptive use of water within the District) can be observed in June, July, hugust, September and October during the past 5 years. November and December show a reduced outflow per unit inflow since 1953 and there are no significant changes in this tendency in the later years. April and May have the same trend change in the past four years. The rest of the months do not show any recognizable pattern changes which could be considered with any confi- dence. , 2. The linear correlation coefficients indicate a very high degree of interrelation of the two variables on both monthly and yearly bases. This indicates that variations in precipitation, storage, and groundwater pumping in the area have only minor affects on the inflow-outflow relation- ships. ~ ,