First-order analysis of open-channel flow

This paper uses first-order reliability methods (FORM) to incorporate randomly variable peak discharge as well as other uncertainties involved in open-channel hydraulics, and compares the results to the traditional method which considers only uncertainty in the discharge. A simple example employing Manning's equation for a compound channel and a Gumbel distribution for design discharges illustrates the advantages of the FORM approach. It is shown that the return period for a depth of flow is less than the return period for the flow normally associated with that depth. This is because in the direct method no uncertainty is accounted for in Manning equation, i. e. converting flow to depth.