Model for hydraulic networks with evenly distributed demands along pipes

This paper shows how the Global Gradient Method formulated by Todini and Pilati (1987) can be modified in order to represent user water demand evenly distributed along pipes. It is also shown how EPANET (Rossman, 2000), which assumes demands to be allocated to the nodes, can be used to represent this type of distributed demand. The proposed procedure is based on an original mathematical method formulated by Messina in 1945. Two different numerical examples relating to networks of different topological complexity are discussed. In particular, it is highlighted that the two different ways of modelling demand lead to different nodal head values and the values are generally lower when demand is evenly distributed along the pipes. However, differences decrease when the piezometric surface is fairly flat over the network (i.e. low water velocities in the pipes). The paper concludes with several considerations regarding the consequences that the method of representing demand has on the processes of calibration and optimal design/rehabilitation of water distribution networks and leakage estimation.