Design of Wastewater Collection Networks Using Dynamic Programming Optimization Technique

Abstract

A computer program for the optimal design of wastewater collection was developed. The program consists of two coupled algorithms. The first is for the generation and assessment of all feasible layouts for the excavation volumes only. The second focuses on the optimal hydraulic design of all links in the collection system. The optimization technique used in the latter algorithm utilizes a dynamic programming method that computes velocities, water depths, pipe slopes, and invert elevations. These algorithms are flexible so that the design criteria could be easily modified or changed. The objective cost function includes the costs of the sewers, sewer construction, hydraulic test, and the construction of the manholes. A least-squares regression analysis was employed for the formulation of the objective function. The objective function was restricted by a set of technological and hydraulic constraints including minimum diameters, flow velocities, depth of excavation, and the invert elevations. A sensitivity analysis was performed to test the effect of the various design variables and constraints. The developed methodology shows the benefit of optimization techniques when compared to the conventional design approaches, and great capital cost savings can be achieved.