OPTIMAL DESIGN OF CULVERTS UNDER UNCERTAINTIES

In the design of highway drainage culverts there are many uncertainties involved in addition to the normally considered hydrologic uncertainty due to the randomness in flood and rainfall frequencies. Uncertainties can be contributed from many sources and are classified as hydrologic, hydraulic, structural, and economic with subtypes of uncertainties in each of these categories. This paper describes a procedure for systematically analyzing and incorporating the uncertainties into the optimal design of drainage culverts. The procedure is based upon the concepts of hydrologic risk, first-order analysis of uncertainties, evaluation of expected damages, and optimization. The optimization model is used to select the magnitudes of the design variables in order to minimize total expected project costs. Using such a design procedure, the proper trade-off analysis among the potential flood damages, the design uncertainties, and the cost of the project is performed in determining the design.