Optimization of water distribution networks : a case study of Moratuwa water distribution system in Sri Lanka

Abstract

Water distribution networks are engineered to provide consumers with an adequate quantity of water at the required pressure. The initial design demands, or water quantities to be delivered, are determined based on factors such as per capita consumption, population growth, anticipated migration, industrial development, and the presence of fire hydrants. Most of the existing water distribution networks are old and operate beyond their design horizon. Therefore, many issues have arisen in the existing systems, resulting in no-water complaints, low-pressure areas, water quality issues, limitations to 24-hour water supply, and consumer dissatisfaction. Hence, modification of the existing pipe networks is necessary to avoid the above issues. However, redesigning and relaying a new system is not practical due to financial limitations. Therefore, augmenting the existing systems has become the best solution for addressing the challenges in the distribution networks. While augmenting the existing networks, proper attention must be given to optimizing the network to minimize operation and maintenance costs, including energy costs. The Moratuwa distribution network in Colombo District, Western Province, Sri Lanka, which is more than 50 years old, was selected for this study. Modeling was carried out using Bentley WaterGEMS software with the aid of the ArcGIS platform. Demand data needed for the modeling were obtained from the bulk flow meters of the supply reservoir of the Water Distribution Network. Simulated results of the computed model were compared with actual field data at selected locations obtained through digital pressure loggers. After calibrating the model, possible options to augment the existing network were analyzed, and prevailing issues that can be minimized were investigated. Three major scenarios were investigated in this study, focusing on the optimization of total operational costs: direct pumping with Variable Speed Drive, direct pumping using an overhead tank as a balancing tank, and entire gravity water distribution by overhead tank