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~ Water & Sewer Authority of Cabarrus County <br />VVO-u~CC Water and Wastewater System Master Plan <br /> <br />Safe Yield Update and Regional Drought Operations <br /> <br />-I <br /> <br />1.3 Stream Flow Evaluation <br />The simulated stream flow record was extended to incorporate flow data through <br />February 28, 2003. Some of the lowest stream flows of record were observed in August <br />and September of 2002. Therefore, the gage weighting factors used to simulate the <br />stream flow record were recalculated to account for the new data. <br /> <br />To evaluate the level of accuracy of the simulated flow record for Lake Howell, it was <br />compared to USGS flow measurements collected Over the last two years in the three <br />streams feeding Lake Howell. The gage weighting factors used to simulate the stream <br />flow record are heavily weighted toward Second Creek values. Therefore, the stream <br />flow record for Second Creek (adjusted to size) was compared to the USGS field- <br />measured data to assess its accuracy of stream flow prediction. <br /> <br />The USGS field data was collected over the period from January 2001 to September <br />2002. The sum of the three stream fl0w values from the tributaries provided the value <br />used to represent total inflow into Lake Ho'veil. <br /> <br />A common flow basis is needed for determination of flow accuracy. Accordingly, <br />Second Creek-gauged values were adjusted, based on drainage area ratio, for direct <br />comparison to Lake Howell inflows. For the days on which the USGS collected Lake <br />Howell inflow data, the actual measurements were compared to adjusted Second Creek <br />flows, and to the synthesized flow record previously used in the safe yield model (also <br />called Weighted Average). The numerical data are presented in Table 1, and the data are <br />shown graphically on Figure 6. <br /> <br /> Table 1 <br /> Comparison of Inflows into Lake Howell (cfs) <br />,, Date USGS at Howell Second Creek Adj. Weighted Average <br /> 1/24/2001 9.27 12.35 16.57 <br /> 7/12/2001 3.43 2.79 7.56 <br /> 9/18/2001 2.11 1.79 3.41 <br /> I I/7/2001 3.40 4.38 6.09 <br /> 1/8/2002 8.01 8.36 16.64 <br /> 2/12/2002 15.40 16.33 24.42 <br /> 3/29/2002 13.28 17.13 22.85 <br /> 4/8/2002 10.89 14.34 16.15 <br /> 5/25/2002 4.51 3.31 6.50 <br /> 7/23/2002 1.08 1.23 2.46 <br /> 8/20/2002 0.16 0.80 3.07 <br /> 9/26/2002 3.47 ! 67 7.03 <br /> <br />PN096873.0800 5 [], <br /> <br />Janua~ 23,2004 <br /> <br />BLACK & VEATCH <br /> International Company <br /> <br /> <br />