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~ Water & Sewer Authority of Cabarrus County VV~CC Water and Wastewater System Master Plan Safe Yield Update and Regional Drought Operations Stream flow can serve as a reasonable predictor of water supply drought; particularly if it is cpmpared to expected monthly values. ,For Lake Howell, a table of expected inflow by month was prepared for use in monitoring actual inflows (Table 5). Table 5 Mean Monthly Inflow to Lake Howell (cfs) Month Mean Flow 75% Mean 50% Mean 25% Mean 10% Mean January 51.8 38.9 25.9 13.0 5.2 February 58'.5 43.9 29.3 14.6 5.9 March 63.5 47.6 31.7 15.9 6.3 April 51.9 38.9 25.9 13.0 5.2 May 38.3 28.7 19.2 9.6 3.8 June 35.0 26.3 17.5 8.8 3.5 July 29.9 22.4 15.0 7.5 3.0 August 31.0 23.3 15.5 7.7 3. I September 2616 20.0 13.3 6.7 2.7 October 31.8 23.9 15.9 7.9 3.2 November 3013 22.7 15.1 7.6 3.0 December 39.7 29.8 19.9 9.9 4.0 Annual 40'.7 30.5 20.3 10.2 4.1 Average For example, the twelve USGS field measurements of inflow to Lake Howell (refer to Table 1) show that flows in 2001 and 2002 were only 10 to 25 percent of the flow expected in those months. Over the period from May 1998 to November 2002, average inflow was between 25 and 50 percent of the expected annual average flow. Mean inflow to each of the four reservoirs during three severe droughts is shown in Table 6 Table 6 Mean Inflow (cfs) during Severe Droughts Drought Period Drainage Area Water Source 4/54 - 6/58 3/86 - 2/87 5/98 - 11/02 (mi2) Lake Howell 35.2 21.3 15.3 47.0 KannaDolis Laket 14.6 11.3 9.5 66.2 Lake Fisher 14.0 8.5 6.1 18.7 Lake Concord 3.5 2.1 1.5 4.7 t Includes drainage area (55.6 sq.mi.) and inflows from Second Creek Pumping Station. PN 096873.0800 14 E'JI, January 23, 2004 BLACK & VEATCH ~__~. ~ International Company