Optimization of Water Tank Design and Location in Water Distribution Systems

Water distribution system (WDS) design has been the subject of minimal improvements over the last decade, despite the fact that the accessibility of computer models has increased. Water distribution pipes are designed to provide adequate pressure at distribution nodes and reasonable velocities in pipes. This is usually done with a hydraulic solver coupled with the engineering expertise of the designer. Storage tanks are designed according to standard requirements considering minimal values provided by local guidelines. Storage tank allocation is generally done without taking into account the network capacity and robustness. Tanks are located next to the distribution area with highest demand and considering other site-specific constraints (topology, multiple pressure-zone systems, etc.). Optimal network configuration, in terms of hydraulic efficiency and water quality, is rarely considered. Long residence time results in the loss of disinfectant residual and favors water quality degradation. Up to now, the optimization of the WDS design and operations have mostly focused on pipe sizing and pumping schedules without taking into account storage tank locations, storage capacity and water quality. The purpose of this paper is to present a new methodology to optimize water storage tank volume and location. This methodology, will take into account hydraulic requirements as well as water quality requirements (by minimizing the residence time in order to reduce disinfectant decay and disinfection by-product formation). The proposed methodology will be tested on a small study case. The optimization model, linked with EPANET, is applied to this benchmark and results are analyzed.