Assessing the spatial distribution of pressure head in municipal water networks

The progressive deterioration of underground water resources, due in great part to the anthropical pressure, and the increasing incidence of pollution phenomena are some of the elements that make a reformulation of water resources management policies necessary. These issues, whose mitigation, if possible, involves great financial investments, have pointed out the opportunity to rationalize the entire production process, both binding the price of the resource to its effective production cost, and diminishing wastes and losses. In this context the problem of the location and the reduction of losses in water distribution networks assumes particular importance. In Italy physical losses are estimated to be approximately 27% of the volume entering distribution systems. They are due both to the state of degradation in which great parts of the distribution systems unfortunately leak and to their bad management. They produce great financial losses, and huge, even if not quantifiable environmental damage. The available methodologies for the individuation of physical losses are generally quite complex and expensive. Physical losses can be concentrated, causing great discharge losses locally, or can be distributed in many small leaks all over the network. It is possible to define a threshold for leakages, above which the economical benefits deriving from the leak individuation and its elimination, are greater than costs. In Italy this value is generally quantified between 5% and 10% of the total volume entering the network. The value of the threshold depends on the value of the distributed water, which includes the cost of supply, of treatment, of conveyance and storage, of pumping, etc., and the “environmental” cost. It increases with the number of leak points, thus resulting in greater costs for the location and repairing of distributed leaks rather than for concentrated ones. In such cases, as these operations are generally unfeasible, in addition to a policy of a medium-long term rehabilitation of the network, an alternative methodology should be followed, based on the optimal management of the network for the control of distributed leakages through the reduction of pressure heads where excessive. First of all a set of measurement devices should be installed for transmitting, in real time, the temporal evolution of pressures in relation to the variability of the demand. It is obvious that the number of instruments should be as small as possible in order to limit the metering system cost. Consequently the values of pressure heads all over the network must be reconstructed from that small number of available measurements. With this aim, a methodology based on the use a spatial interpolator of “regionalized variables” is proposed and discussed in this paper. The knowledge of pressure heads all over the network can be then employed in the formulation of optimal valves management in order to obtain pressure reductions and therefore the control of physical losses.