On the approximation of distributed demands as nodal demands in WDN analysis

The analysis of a looped water distribution network, operating under pressure and in steady flow conditions, can be accomplished once the topology of the network, the geometry of the pipes, the water demands delivered at the nodes and the head value at least one node are known. In a water distribution network (WDN) model water demands are represented as delivered at the nodes although they occur along the pipes. This classical approximation represents the total demand along the pipe as two lumped demands at its ending nodes. This paper demonstrates that the above approximation is wrong, because it generates head loss errors which may be significant when the network analysis is performed for calibration or for network design purposes. Therefore, an extension of the Global Gradient Algorithm for network analysis is here proposed which allows to correctly introduce the lumped nodal demands without loosing the physical correct representation of head losses.