Model for Layout and Design of Sewer Systems

An optimization model has been developed for computing the minimum cost layout and design of sewer systems for arbitrary topographic, physiographic, and hydrologic conditions. The heuristic procedure has been developed as a screening model consisting of two conjunctive phases: a combined layout and design model and a design model for given layouts. The combined layout and design model is an optimization procedure based upon discrete differential dynamic programming (DDDP) and a connectivity model formulated as a set-partitioning problem. This iterative stage-by-stage procedure results in a complete system layout and design after each iteration. The design model for given layouts is also based upon DDDP and is used to compute the minimum cost designs for layouts generated by the combined model. Through the use of a hypothetical example several factors affecting efficient use of the layout and design model are identified and examined.