Optimizing Hydraulic Design of Highway Drainage Systems

This paper presents a computational methodology and software model for direct evaluation of optimal highway drainage inlet design. The optimal design is defined as the most economical combination of stormwater inlet type, size, and location subject to a maximum width of gutter spread. The problem is formulated as a discrete-time optimal control problem in which a genetic algorithm is interfaced with a hydraulic simulation model. The simulation model follows guidelines established by the Federal Highway Administration and is used to implicitly solve governing hydraulic constraints that yield gutter discharge, inlet interception capacity and spread according to a design storm. The genetic algorithm is used to select the best combination of design parameters and thus solves the overall optimization problem. The new methodology allows for a reduced total cost of highway drainage since its primary aim is to minimize user-defined costs that can be associated with materials, initial construction and long-term maintenance. Capabilities of the model are demonstrated through application to a hypothetical highway drainage system. The example reveals that genetic algorithms and the discrete-time optimal control methodology comprise a comprehensive decision-making mechanism that can be used for cost-effective design of storm water inlets.