CHANCE-CONSTRAINED MODEL FOR STORM-WATER SYSTEM-DESIGN AND REHABILITATION

A mixed integer chance constrained optimization model was developed to determine design and rehabilitation management strategies for storm-w ater drainage systems conditioned on the likelihood of exceeding the s ystem's conveyance capacity. The model is multiobjective in nature and capable of considering multiple design or rehabilitation alternatives . Model objectives include the minimization of cost and probability of system failure. The probability that storm-water flows exceed the con veyance capacity of any network segment within the system is expressed as a chance constraint. The model combines kinematic wave routing met hods and second-moment analysis to formulate the chance constraint. In this manner, only the mean, variance, and form of the distribution of the storm-water flows are needed to formulate the deterministic equiv alent optimization model. To illustrate the model, an example is prese nted using an existing storm-water drainage network at Duke University , Durham, North Carolina. Results of this example specify the most cos t-effective storm-water network design at varying system reliabilities . These results define trade-off relationships between total system co st and the probability of system failure.