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~ Water & Sewer Authority of Cabarrus County <br />VVSACC Water and Wastewater System Master Plan <br /> <br />Safe Yield Update and Regional Drought Operations <br /> <br />30 <br /> <br />25 <br /> <br />20 <br /> <br />0 <br /> <br />Figure 6. Comparison between simulated records and L~SGS stream flows at Lake Howell <br /> <br />The comparison of flows showed that the Weighted Average record overestimated the <br />low flows observed at Lake Howell. The Second Creek values, adjusted to a comparable <br />drainage area, are much closer to the actual Lake Howell inflows. Overall, they <br />overestimated flows slightly over the period analyzed. <br /> <br />Additionally, a correlation analysis was performed on the three sources of data to provide <br />a statistical determination of the accuracy of flow prediction. The correlation coefficient <br />(R) 'is an index of the degree of association between two values. The correlation <br />coefficient measures the degree to which the measured and predicted values agree, and is <br />used as a measure of the accuracy of future predictions. A correlation coefficient greater <br />than 0.7 indicates a significant degree of association between the measured and predicted <br />values. The results of the correlation analysis show that both the weighted average- <br />generated flows and Second Creek values associate extremely well to field-measured data <br />for Lake Howell. <br />· Correlation between USGS measurements and Second Creek flows, R = 0.98 <br />· Correlation b~etween USGS measurements and weighted average flows, R = 0.98 <br />· Correlation between Second Creek and weighted average flows, R = 02J6 <br /> <br />PN096873.0800 6 <br /> <br />Janua~ 23,2004 <br /> <br />BLACK & VEATCH <br /> Intemltlonll Company <br /> <br /> <br />