Assignment #10b - GA/QP Model to optimize sewer systems

Review Article

1) Article Reference
Pan TC, Kao JJ (2009) GA-QP Model to Optimize Sewer System Design, JOURNAL OF ENVIRONMENTAL ENGINEERING, 135(1) 17-24

2) Summary
This paper presents an application of genetic algorithms to optimize the design of a sewer system. A case study is presented to illustrate the methodology using system composed of 79 links, 56 nodes and a drainage area of 260 ha.
The author’s presents a discussion of the complexity of designing a sewer system targeting the minimum cost, maintaining the system hydraulic and construction constraints. A description of the concepts of genetic algorithm is also presented including all its elements and behavior. For this problem the decision variable of the sewer are coded as genes and each chromosome represents one design. The first constraint assures that the pipe has enough flow capacity, the second constraint takes care of ensuring the downstream pipe has diameter equal or greater then the upstream neighbor. It is also considered the possibility of installing a pump in each node. The fitness function is used considering the construction cost of the network. A description of the selection, crossover and mutation methods is provided. For this particular study, the author used also a quadratic programming (QP) model, to improve efficiency, the nonlinear cost fitness function was approximated to a QP. The design parameters for this case study were the maximum velocity, minimum velocity, minimum slope, maximum proportional water depth and minimum cover depth. To avoid finding a solution which was not the true best, due to simplifications or factors that are hard to formulate into the model, it was also used a MGA function.
Different results for the case study were presented achieving a minimum cost of approximate 1.7 million dollars. According to the author the GA and quadratic model approach were satisfactory to find a good solution for the problem.

3) Discussion
It really surprised me to see that this paper was published in 2009 and nobody had ever tried such approach for solving sewer systems network. After all our classes, I felt quite confident in understating all the terminology and the methodology for solving the GA presented in this paper. Actually I think the paper had even too much of GA theory instead of new contributions for science. The best part, I think, is that I feel very encouraged to apply GA optimization methods for my research area.