An assessment of node–head–flow relationships at lumped demand nodes for pressure-dependent analysis of water distribution networks

ABSTRACT Pressure-dependent analysis (PDA) is preferred over demand-dependent analysis (DDA) to evaluate the performance of any water distribution network under pressure-deficient conditions. The PDA requires a relationship, called node–head–flow relationship (NHFR) between available head and available flow at a node to know whether the demand is fulfilled completely, partially, or not at all, depending on the available pressure. Several types of NHFRs have been suggested in the past and mostly a single type of NHFR is used at different nodes. An assessment of these NHFRs is carried out to know how accurate the use of a single type of NHFR is for the lumped nodes. The errors in prediction of the available nodal flows through the available NHFRs and that obtained through the detailed analysis are quantified using chi square. It is observed that actual NHFR is not as smooth as approximated by the different available NHFRs. A nonlinear behaviour between available flows and available heads exists for partial flow conditions and requires proper values of constants to define any NHFR. Furthermore, NHFRs at different lumped nodes in a network are different. This study recommends the consideration of different relationships at different lumped nodes of the network for PDA.