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~ Water & Sewer Authority of Cabarrus County <br />V~--~CC Water and Wastewater System Master Plan <br /> <br />Safe Yleld Update and Regional Drought Operations <br /> <br />Safe Yield Update and Regional Drought Operations <br /> <br />The water sources within Cabarms and Rowan Counties which serve the entities in <br />Cabarms County include Lake Howell, Kannapolis Lake, Lake Concord, Lake Fisher, <br />and Black Run Reservoir. The existing,service areas of each.entity and the location of <br />the lakes are show in Figure 1. <br /> <br />1.0 Safe Yield Update <br />The severity of the recent drought has resuZted in record low stream flows, low reservoir <br />levels, emergency water supplies from sources outside Cabarms County, and extended <br />mandatory water restrictions. Using the mass-balance model to simulate reservoir <br />operations, it can be shown that the recent drought (1998-2002) was the most severe in <br />the last 103 years of record with respect to reservoir yield and reliability. To quantify the <br />effects of the recent drought, it was necessary to update the mass-balance models. The <br />update includes the new drought of record for the four major .water supply reservoirs <br />serving Cabarrus County: Lake Howell, Kannapolis Lake, Lake Fisher, and Lake <br />Concord. In addition, the collection of bathymetric information for these reservoirs <br />coupled with a better representation of the inflows to the reservoirs needed ~o be <br />incorporated into the safe ~ield calculations. <br /> <br />1.1 Mass-Balance Model Approach <br />The model used to analyze the reservoirs calculates the average annual yield for the <br />reservoir based on constant demands imposed on simulated historical hydrologic data and <br />current reservoir geometry. Yield is determined by solution of a water balance equation <br />using an iterative approach. Solution of .the water balance equation occurs when the <br />difference in reservoir inflow and outflow equals the change in reservoir storage volume. <br />Model inflows include precipitation and stream flow into the reservoir. Outflows include <br />evaporation, user demands, spillway overflows, and downstream releases. The following <br />water balance equation is used in the reservoir yield model: <br /> <br />VOL/= [VOLo + INFLOW + PRECIP] - [YIELD + EVAP + SPILL + MIF] <br /> <br />The variables in the equation are defined as: <br /> <br />VOL~ <br />VOL0 <br />INFLOW <br />PRECIP, <br />YIELD <br /> <br />= reservoir volume at the end of the month. <br />= reservoir volume at the beginning of the month. <br />= volume of inflow during the month. <br />= volume of precipitation on reservoir during the month. <br />= average volume of yield during the month. <br /> <br />PN 096873.0800 <br />Janua~ 23,2004 <br /> <br />BLACK & VEATCH <br /> Intarnltlonal Company <br /> <br /> <br />