STOCHASTIC STORM TRANSPOSITION COUPLED WITH RAINFALL-RUNOFF MODELING FOR ESTIMATION OF EXCEEDANCE PROBABILITIES OF DESIGN FLOODS

The stochastic storm transposition (SST) technique has been developed and evaluated in previous studies for the estimation of exceedance pro babilities of extreme precipitation depths. In this study it is extend ed to the estimation of exceedance probabilities of extreme design flo ods, The link between storms and flood peaks is provided by a rainfall -runoff transformation and stochastic descriptions of antecedent moist ure conditions and storm depth temporal distributions. Cumulative aver age catchment depths produced by the SST approach have been converted to a range of possible flood peak values using a rainfall-runoff model (the ARNO model) and a probabilistic disaggregation scheme of cumulat ive storm depths to hourly data. The analysis has been repeated for a range of fixed antecedent moisture conditions. The probabilities of ex ceedance of the produced flood peaks have been estimated and compared to highlight the effect of antecendent moisture conditions on the magn itude and frequency of produced floods as compared with the magnitude and frequency of the corresponding average catchment depths.