Probabilistic Design of Open Drainage Channels

Abstract

A method for designing open drainage channels that incorporates the uncertainty associated with various design variables is presented. The design involves two random components: runoff (demand) and channel capacity (supply). The runoff is formulated considering the uncertainties of rainfall intensity, drainage area, and other watershed characteristics. The channel capacity is formulated considering the uncertainties of channel friction factor, longitudinal slope, channel width, side slope, and water‐flow depth. The probabilistic characteristics of the runoff and channel capacity are established based on the first‐order principle of probability theory. A reliability index that can be used to design an open channel to convey runoff for a given probability of failure is developed. This probabilistic approach should be valuable in the design of open drainage channels whose runoff and capacity variables are generally uncertain.