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3.2 Emma Gage Correlation <br />Average monthly streamflow data from the Emma gage for April — October was correlated to the <br />corresponding monthly data from the downstream Glenwood Springs gage resulting in the following <br />correlation equation: <br />Emma gage flow in cfs = Glenwood gage flow in cfs X 0.4715 + 53.04 <br />The correlation coefficient of R2 = 0.94 indicates a statistically good correlation. The data and results are <br />graphically depicted in Figure 3. <br />A second correlation using monthly data for the entire year (January — December) was also completed. <br />The results were insignificantly different from the April — October correlation so the former was used for <br />development of RICD reach flows. <br />Utilizing the correlation equation and the historical mean daily flow values for the Glenwood gage for the <br />period from 1907 — 2004, a long term daily record for the Emma gage was developed. This long term <br />synthetic gage record then became the basis, after irrigation adjustments, for determining the flow — <br />exceedence values in the RICD. <br />3.3 Irrigation Adjustment <br />Five ditches irrigate nearly all the irrigable land between the Emma gage and the RICD reach. Flood <br />Irrigation is predominant. Two of the ditches divert above the gage but irrigate land below the gage while <br />three of the ditches divert below the gage. Return flow from all the ditches accrues to the river above the <br />RICD reach. To determine an appropriate Emma gage adjustment the estimated depletion / accretion <br />from the five ditches was evaluated. <br />The ditch evaluation is summarized in Table 2. First, average monthly diversion records from the <br />Colorado Decision Support System (CDSS) were tabulated. Second, based on the assumption that flood <br />irrigation is 30% efficient, the net irrigation depletion between the gage the RICD reach was determined. <br />For the two ditches that divert above the Emma gage, this meant that 70% of the water diverted returned <br />to the reach and had to be added into gage record. For the three ditches that divert below the gage, 30% <br />of the average diversions were subtracted from the gage. The result is a net gage reduction, by month, <br />ranging from a low of 1 cfs in April to a high of 29 cfs in August. <br />X <br />