RELIABILITY-ANALYSIS OF HYDRAULIC STRUCTURES CONSIDERING UNIT-HYDROGRAPH UNCERTAINTY

Unit hydrographs (UHs), along with design rainfalls, are frequently us ed to determine the discharge hydrograph for design and evaluation of hydraulic structures. Due to the presence of various uncertainties in its derivation, the resulting UH is inevitably subject to uncertainty. Consequently, the performance of hydraulic structures under the desig n storm condition is uncertain. This paper integrates the linearly con strained Monte-Carlo simulation with the UH theory and routing techniq ues to evaluate the reliability of hydraulic structures. The linear co nstraint is considered because the water volume of each generated desi gn direct runoff hydrograph should be equal to that of the design effe ctive rainfall hyetograph or the water volume of each generated UH mus t be equal to one inch (or cm) over the watershed. For illustration, t he proposed methodology is applied tb evaluate the overtopping risk of a hypothetical flood detention reservoir downstream of Tong-Tou water shed in Taiwan.