Effect of rainfall errors on accuracy of design flood estimates

Abstract

A procedure is presented to explicitly evaluate the effect of estimation errors in the temporal and spatial distribution of rainfall on the uncertainty of calibrated rainfall‐runoff model parameters. The effect of this uncertainty on the reliability of design flood predictions is considered. A case study of the Hacking catchment, south of Sydney, Australia, is presented to illustrate the procedure. For a major storm event a simple stochastic transformed rainfall model is calibrated and validated using kriging and then used to infer the mean and covariance of subareal rainfall. The RORB model, a distributed nonlinear rainfall‐runoff model, is calibrated to this storm event. When allowance is made for uncertainty in the calibration event rainfall, the results indicate that the uncertainty in the calibrated parameters increases, especially in the rainfall excess parameters, and the 90% prediction interval on the 100‐year design flood increases by about 100%.