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~ Water & Sewer Authority of Cabarrus County V~CC Water and Wastewater System Master Plan Safe Yield Update and Regional Drought Operations 2.4 Drought Operating Curves 2.4.1 Seasonal Considerations. For reliable and safe reservoir operation, it is desirable for the reservoir to be nearly full in the Spring, prior to the onset of low flow, high evaporation, and high water demand months. Likewise, it is expected that the reservoir will drop to its lowest acceptable levels in the early Fall, following the same high water use months. These two empirical objectives are used to define the upper and lower bounds of usable volume, for each stage of drought, when seasonal effects are considered. The proposed drought operating curves reflect ,these complementary annual cycles. 2.4.2 Minimum Release from Lake Howell In addition to stipulating water usc reductions, each stage of drought restriction is proposed to coincide with a reduction in the minimum release from Lake Howell. The NCDENR Administrative Code provides consideration of reductions in specified minimum release from a dam. The language can be found in Title 15A, Subchapter 2K - Dam Safety, Section 0500, (http://www.dlr.enr.state.nc.us/Titlel5A SubCh2K. html). Preliminary conversations were held with representatives of the Instream Flow Unit of the Division of Water Resources and others with expertise in the water supply program and biological resources to discuss the development of a tiered release approach for the dam at Lake Howell. The protection of base flows in Coddle Creek downstream of the dam was identified as a principal objective to sustain biological habitat. Preliminary guidance was to devise a release schedule that would provide water supply relief earlier in the drought, to reduce the frequency of calling for severe stages of drought restrictions and dam release reductions later in the drought. A number of options were modeled, and the following tiered release system was selected because Stage 4 drought restrictions would have occurred only once during the period of time simulated. Only during the severe drought experienced from 1998 to 2002 would the implementation of Stage 3 and 4 drought restrictions have been required. For purposes of evaluating the proposed drought curves, the required minimum release from Lake Howell is reduced from 6 cfs in normal conditions to 3 cfs during Stage 1 drought restrictions; to 2 cfs during Stages 2, 3 and 4 restrictions. Water withdrawal reductions from Lake Howell of 10, 10, 20, and 25 percent are planned to coincide with PN 096873 0800 18 January 23, 2004 BLACK & VEATCH ~ ,. ~1~ International Company