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<br />flow have a long period of record, which is ordinarily <br /> <br />required in mass diagram analysis. The Purgatoire River is <br /> <br />the only tributary having long term streamflow records. <br /> <br /> <br />The diagram exhibits a fairly constant slope from 1908 <br /> <br />to 1943. See, Graph 5C, Ref. 11. After 1943 the slope <br /> <br />increases, corresponding to the time when John Martin <br /> <br />Reservoir went into operation. The slope then declines in <br /> <br />about 1951 and remains fairly constant until 1974 when a <br />significant decline in slope is evident. Starting in about <br />1980 the slope increases again, though not to the magnitude <br />of the pre-1973 slopes. This diagram indicates that <br />starting in 1952 the usable stateline flows showed some <br />decline in relation to the index flows and that in 1973 a <br /> <br />dramatic decline in this relationship occurred. The diagram <br /> <br />also shows a slight decline starting in 1962 which is <br /> <br />interrupted by the flood of 1965. The declines evident may <br /> <br />be the result of several factors, including alluvial well <br /> <br />development in Colorado, declines in tributary inflows, and <br /> <br />changes in the operation of John Martin Reservoir starting <br /> <br />in 1980. Increased transmountain return flows have also <br /> <br />accrued to the river during the postcompact period. The <br /> <br />'changes noted on the diagram are the net result of the <br /> <br />various changes which have occurred and are not likely <br /> <br />attributable to a single change. <br /> <br />4. Initial Use of the Conservation Pool of John Martin <br />Reservoir <br /> <br />As noted in the Kansas' first report, several of the <br /> <br />single and double mass diagrams show breaks in slope <br /> <br />-29- <br /> <br />a_ <br />