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<br />001548 <br /> <br />An analysis based on 90 traces implies that 90 different 54 year examples of possible hydrology <br />were assembled (based on the historic hydrology) and used to simulate the operation. To <br />generate different examples from the historical hydrologic sequence, traces of data are assembled <br />by beginning the first year of data for each trace at a different hydrological starting year. For <br />example one trace would start with year one being the hydrology of 1906, while the next trace <br />would start at a different hydrologic year. To allow the user flexibility in assembling a cross <br />section of typical traces, the size of the "step" can be specified. For example, as shown in <br />Figure 5, 10 traces were programed for, with a trace step size of9, and first year hydrology of <br />1906. Notice that Trace 2 starts with year 1915 hydrology, and Trace 3 with year 1924 <br />hydrology. <br /> <br />Figure 5 also shows why a graph containing all 90 traces of a normal run would not be practical, <br />except to show the outer limits (maximum and minimum results) of operation. With all the lines <br />and dots the center area would be different densities of black. As graphing all 90 traces is not <br />practical, averages, distribution by selected years, or selected exceedances for all years are <br />determined and graphed. <br /> <br />Wrapping Around the Hydrologic Data. While the historical hydrologic sequence is held <br />intact (1908 hydrology will always follow the 1907 hydrology, etc.) 90 years of data allows you <br />to assemble up to 90 traces. When assembling the data, if the sequence of yearly hydrology <br />requires data past 1995, the historical data is "wrapped around" such that 1906 data will always <br />follow 1995 (or the last, most recent year of hydrologic data). As shown in Figure 5, the <br />Traces 6 thru 10 which start after 1942 would not have enough hydrologic data in that 1906 thru <br />1995 natural data to fill out 54 years. In these traces, following 1995, the hydrologic data picks <br />up with 1906 data and continues. . <br /> <br />8 <br />