Water Supply Yield Analysis for Washington Metropolitan Area

Abstract

The Washington D.C. Metropolitan Area (WMA) has experienced rapid population growth in the 1980s. Water supply yield analysis techniques are developed in this paper to assess adequacy of the current WMA water supply system to meet escalating future demands for water. In the statistical model developed for analyzing water supply yield, “annual yield” is a random variable representing the maximum yield the water supply system can provide in a given year. Randomness in annual yield may be attributed solely to randomness in supply or to randomness in both supply and demand. Annual yield random variables are dependent on the operating rules used for the two upstream reservoirs that serve the WMA. The dependence is simple because the operating rules are completely specified by past streamflow and two “operating parameters.” The operating parameters are chosen to maximize specified attributes of the annual yield distribution, represented by the “weighted yield.” The sum of the historic yield values of the individual components of the WMA water supply system is 482 mgd, a value dangerously close to current mean water use. Historic yield values for the joint system yield models exceed 700 mgd, indicating that the current water supply system is quite reliable.