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The selected baseflow nodes were plotted against time for the period 1909 through 1996. The <br />plots were too closely matched to see a significant difference. Figure 2 demonstrates the typical <br />variance at the Yampa River below Stagecoach Reservoir gage, shown here for the period 1974 <br />through 1996. The flow pattern remains similar, with variance in the months following the <br />largest diversions. This indicates that total return flows have been generally increased, since <br />baseflows are determined by adding upstream diversions, which are constant between the <br />simulations, and subtracting corresponding return flows. <br />Figure 2 <br />Yampa River Below Stagecoach Reservoir -Gage 9237500 <br />Original Baseflows and New Baseflows <br />35000 <br />30000 <br />25000 <br />:a <br />~ 20000 <br />O <br />d <br />R 15000 <br />a <br />t <br />c 10000 <br />0 <br />E <br />5000 <br />0 <br />-5000 <br />h! <br />I <br /> <br /> <br />li p <br />~ ~l <br /> i I ~ II <br />~ II <br />i <br />I I ` <br />I I <br /> <br />I ^ <br /> <br /> <br />~~ ~ + ~ <br /> <br />I ~~ i i! <br />~ u <br />~~ I ~ ~~i <br />I^ i i ~I <br />~ <br />~ <br />I' <br />~ <br />I ~ <br />~~ <br />~ <br />i Iii I~ q ~ <br />~ i ~ i <br />'II ~ <br />i <br />I <br />i I i <br />~ r~ <br />~ h i I M ~ I M. I I~ i ~, G~ ~ ~~ I ~" I ~~ ~~ ~ II <br />d <br />rn v rn v <br />~ ~ ~ rn <br />rn rn rn rn <br />new --- original -difference (original -new) <br />Scatter plots for each of the seven gages, graphing the monthly baseflows calculated using the <br />new StateMod algorithm against the original monthly baseflows for the period 1909 through <br />1996, are presented in Figures 3 through 9. As shown on the graphs, the correlation between the <br />new and original baseflows is very close, showing minor change between the two baseflow data <br />sets. The best-fit lines used to determine the correlations were forced through the coordinate 0,0; <br />however, the change in correlation was insignificant when the best-fit lines were allowed to vary. <br />Table 1 shows the average annual baseflows at each location for both the original and new <br />simulations and the percent difference based on the original values. Note that, on the average, <br />baseflows have been reduced using variable efficiency and soil moisture accounting. <br />This indicates that, on the average, return flows have increased. This likely reflects that when <br />the variable efficiencies are lower than the average efficiencies and diversions are large, as with <br />wet months, much more water is returned to the river. Note that although the variable efficiency <br />calculation also affects dry months when efficiencies are higher than the average, because dry <br />month diversions are small, the incremental change in return flows is also small. <br />L:ASecrion Folders\SECD\Carolyn\CDSS\VariableEff Taskl-3.doc 7 of 16 <br />