BOOTSTRAP POSITION ANALYSIS FOR FORECASTING LOW-FLOW FREQUENCY

A method of random resampling of residuals from stochastic models is u sed to generate a large number of 12-month-long traces of natural mont hly runoff to be used in a position analysis model for a water-supply storage and delivery system. Position analysis uses the traces to fore cast the likelihood of specified outcomes such as reservoir levels fal ling below a specified level or streamflows falling below statutory pa ssing flows conditioned on the current reservoir levels and streamflow s. The advantages of this resampling scheme, called bootstrap position analysis, are that it does not rely on the unverifiable assumption of normality, fewer parameters need to be estimated directly from the da ta, and accounting for parameter uncertainty is easily done. For a giv en set of operating rules and water-use requirements for a system, wat er managers can use such a model as a decision-making tool to evaluate different operating rules.