Pipe hydraulic resistance correction 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 at the nodes and the head value of at least one node are known. In a water distribution network (WDN), water demands are assigned to the nodes, although in reality they are distributed along the pipes converging at such nodes. This classic assumption represents the total demand along a pipe as two lumped withdrawals at its terminal nodes. This paper demonstrates that the above approximation is wrong because it generates head loss errors which may be significant when network analysis is performed for calibration, system design, real-time operations, rehabilitation strategies, optimal operation studies, reliability analyses, etc. Therefore, an extension of the global gradient algorithm (GGA) for network analysis is proposed which entails a modified GGA permitting the effective introduction of the lumped nodal demands, and without forfeiting a correct physical representation of head losses, by means of a pipe hydraulic resistance correction.