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~ Water & Sewer Authority of Cabarrus County WSA~ Water and Wastewater System Master Plan Safe YieldlJpdate and Regional Drought Operations Drought Stages 1, 2, 3 and 4, respectively. Mean monthly inflow values are reported in Table 5. 2. 4.3 Proposed Drought Operating Curves. Percentage of usable volume, reservoir pool elevation, and frequency of drought restrictions were factorg in the derivation of the drought curves. An evaluation of several combinations resulted in the following criteria used for the Stage 1, Stage 2, Stage 3 and Stage 4 drought curves, as presented on Figures 13 and 14. The curves are based on the percentage of usable volume in Lake Howell and consider seasonal variations in storage in Stages 3 and 4. The basis of and actions planned for each stage of drought follow: · Normal: over 70 percent of the usable volume remaining in Lake Howell and reservoir inflow is above 75 percent of the historical mean monthly flow for the corresponding month (see Table 5); minimum release = 6 cfs; water withdrawal reduction from Lake Howell = 0 percent. Stage 1: over 70 percent of the usable volume remaining in Lake Howell, but reservoir inflow is below 75 percent of the historical mean monthly flow for the corresponding month (see Table 5); minimum release = 3 cfs; water withdrawal reduction from Lake Howell = 10 percent. Stage 2:70 percent of the usable volume remaining in Lake Howell; minimum release = 2 cfs; water withdrawal reduction from Lake Howell = 10 percent. · Stage 3:60 percent to 40 percent of the usable volume remaining, depending on month; minimum release -- 2 cfs; water withdrawal reduction from Lake Howell = 20 percent. ' · Stage 4:50 percent to 30 percent of the'usable volume remaining, depending on month; minimum release = 2 cfs; water withdrawal reduction from Lake Howell = 25 percent. A summary of storage volume and reservoir pool elevation data used to develop the operating curves is in Table 7. As shown, the operating curve arrangement triggers the four drought stages, depending on the month of the year. Washwater from the Coddle Creek Water Treatment Plant discharges continuously into Coddle Creek downstream of Lake Howell. In addition to the releases from Lake Howell indicated above, 1 cfs will credited for the discharge from the treatment plant. When additional raw or treated water is delivered to Cabarrus County to meet the long-term water supply needs of the entities of the county, the 1 cfs credit from the water treatment plant will be rescinded. Figure 15 shows the location of the Coddle Creek WTP in relation to Lake Howell. PN 096873 0800 Janua~ 23,2004 BLACK & VEATCH International Company