First‐Order Analysis of Open‐Channel Flow

The effects of uncertainty in Manning's roughness coefficient and the empirical nature of Manning's equation on return period of flood stages have been analyzed using first-order reliability methods (FORM). This method generally used for structural reliability was applied to hydraulics by using Manning's equation as the basis for a limit state function. This paper also describes a way to compare the FORM results, a safety index, to the results of the traditional frequency method, a probability, by changing both to a return period.