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■ <br />NEBRASKA'S ANALYSIS <br />It is evident from Figure 2 that the NDWR used only a portion of the <br />available USGS flow data in constructing its mass curve. It would appear <br />that the only data relied upon for that analysis were data contained in the <br />Hydrodata2 computer database. While what data is contained in Hydrodata <br />is generally very accurate, there are occasional data gaps which must be <br />filled by reference to other sources. Appendix A contains an excerpt from <br />Water Supply Paper 13103 which, in conjunction with the computer database <br />values, provides a complete set of data for the Julesburg gage. <br />In order to analyze the relationship between the slope of the trendline <br />appearing in the July 18 Nebraska report and the cumulative mass analysis <br />curve resulting from the use of a complete set of data for the 1902 to 1986 <br />period, we superimposed the July 18 trendline on the curve in Figure 5. <br />Because the July 18 Nebraska report failed to provide a correlation <br />coefficient or slope value for the trendline it used, we developed these <br />values ourselves. In making our comparisons, we found that the July 18th <br />trendline would come close to fitting only that portion of the full data <br />cumulative mass analysis curve for the interval between 1916 and 1969. The <br />use of such a limited interval trendline ignores, and thus masks, the very <br />significant slope break which commences in 1956. It thus produces a <br />misleading and erroneous result. <br />Hydrodata, USGS Daily Values - Western Region, 1850 to Present. <br />CD -ROM Database. Volume 2.0. US West Optical Publishing, Denver, Co., 1988. <br />3U .S. Geological Survey Water Supply Paper 1310 Compilation of <br />Records of Surface Waters of the United States Through September 1950, Part <br />6B. Missouri River basin Below Sioux City Iowa, 1958. <br />