Including uncertainty in the unit hydrograph method

Abstract

The unit hydrograph method is reformulated into a stochastic integral equation for use in preparing probabilistic distributions of design criterion variable values (e.g., pipe size, basin volume, peak flow rate, etc.). By discretizing the ensemble of possible transfer functions (e.g., unit hydrographs) and weighting the resulting finite set of realizations, the stochastic integral equation can be more simply utilized in practical engineering problems. In this paper, a weighted set of mass curves are prepared for use in the Los Angeles, California, region. The weighted mass curves reflect the probabilistic weighting of the corresponding distribution of transfer functions used to convolute with effective rainfall (i.e., rainfall less losses) to produce runoff estimates.