Agenda - 03-02-2006-7b - Laserfiche WebLink

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drinking water for certain non-potable purposes, such as heating and cooling, on the main campus.) ^ Green Lines: firture demands with the OWASA/UNC reuse project on the main campus in place and operating in 2008, The "Less Reuse" and "More Reuse" boundaries indicate the likely rarrge of future demands, OWASA's projections reflect all information currently available about ongoing and planned development on the University's main campus and Carolina North, but do not include any allowance for demands that could be met by water reuse at Carolina North, The basis for these projections is discussed later in this report.. ^ Black Stepped Horizontal Lines: the capacity of OWASA's University Lake/ Cane Creek/Stone Quarry reservoir system as currently configured, with planned pump improvements, and with the Quarry's eventual expansion in the early 2030s, The upper stepped line is the reliable "safe yield" of the system under drought conditions that would be expected to occur approximately once in 30 years, The lower stepped line is the safe yield under the drought-of-record conditions that occurred in 2001-2002. The intersection of the diagonal demand lines in Figure 1 with the horizontal capacity lines represent periods when anticipated demand will equal or exceed the estimated safe yield of the reservoir/quarry system, This does not mean that we will run out of water at that time; but, the system will only be able to provide the indicated amount of wcztet• if the 30~~eat° or 1001 drought-of-record should recur. On the basis of nearly 80 years of hydrologic records, the probability that .30-year drought conditions will not occur in any given year is 29 out of 30, or nearly 97 percent. In other words, there is a 97 percent chance that the reservoir/quarry system will produce more than the specified safe yield in any given year. The probability of exceeding the record drought yield (which is less than the 30-year yield) is even greater. The probability of depleting OWASA's reservoir/quarry system under various conditions of supply and demand is illustrated in Figures 2, .3, and 4. These figures also provide graphic guidelines for determining when to invoke different levels of OWASA's water conservation standards, ^ Each cell of the table contains an integer and a percentage, which represent the probability that reservoir levels will decline to 20 percent or less of full capacity during the following 18 months, These results were derived from spreadsheet model runs of almost 80 years of daily streamflow data, updated through January 200.3, and driven by monthly water demand and reservoir storage at the begimiing of each month, Calculations were based on average amoral raw water withdrawals of 9.15 million gallons per day (mgd) for Figure 2; 10 mgd for Figure .3; and 11 mgd for Figure 4, and adjusted with shorter term demand ratios, which are reflected in monthly demands shown at the top of each column. (Actual reservoir withdrawals during 2005 averaged 8.4 mgd,) OWASA - Water and Sewer Capnci(y /mplicntioas of G~creased Development Densi(y Pnge S of 2!