Historic Flow Trends at Julesburg, Colorado

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Moreover, as can be seen from Figure 5, there are obvious changes in the slope of the cumulative flow line both before 1916 and after 1969. The July 18 report grudgingly recognizes a change in slope between 1971 and 1985, but tries to attribute that phenomenon to "an acknowledged wet period with several record setting flows ". A cumulative mass analysis minimizes the effects of short term variations in flows due to single wet or dry years. Only a series of wet years (wet cycle) or dry years (dry cycle) can significantly effect the analysis. In Colorado, during the 1971 to 1985 period, the only acknowledged wet cycle is comprised of the years 1983, 1984, and 1985. These sequential extreme high flows occurring in the years following 1982 do not affect the slope of the cumulative mass flow diagram until 1983 (see Figure 1). Figure 6 shows the historic annual flows at the Julesburg gage. A visual examination of the figure in the time period between 1969 and 1982, shows a relatively normal range of annual flows and contains both high flow years (1980) and drought years (1977- 1978). We have had the opportunity to review the report prepared by Hurr et. al. The authors of that report indeed found that South Platte flows did not decrease at Julesburg during their study period (1947 - 1970), although a decrease would be expected as a result of increased groundwater pumping, municipal use and drought. The authors say the expected decrease was avoided due to reduced surface water diversions and "transmountain diversion water entering the study area" (emphasis added). Because the study only extended until 1970, it can have no validity for use in developing flow trends occurring beyond 1970. - 12 -