Joint Consideration of Layout and Pipe Sizes for Water Distribution Network Design with Reliability

In a looped water distribution network (WDN) alternate paths are available for supply in case a pipe fails and isolated from the network. The provision of minimum size or minimum flow carrying capacity of each pipe in a least-cost design of WDNs, or deciding layout of a looped WDN such that at least two-pipes are connected at each node may assure connectivity but not sufficient capacity of the network to meet demands during failure of any pipe. Reliability of looped network increases with increase in number of pipes at each node, or increase in pipe sizes; however, the cost also increases. Thus, reliability-based design should consider both layout and pipe sizes optimization. Methodologies based on entropy have been suggested for selection of layout and design to consider reliability [1,2]. A new methodology, based on flow uniformity in the network, is attempted for the selection of network layout. The flow-uniformity is assessed through variance of flow-series. It is observed that in a branched network, the variance of pipe-flows is maximum; and the reliability of the network increases as the variance decreases by adding loop-forming links. A heuristic methodology is suggested to obtain a layout with minimum variance. The layout so selected is optimally designed using linear programming. The methodology is applied to a simple problem and cost and reliability values are compared. Further, a network from the literature [3] is considered. The reliability consideration is observed to have a layout with more number of pipes as compared to that obtained for minimum cost design.