This paper presents a methodology to evaluate the reliability of water distribution systems that can be used in the design phase and for identifying repair works to be carried out on existing systems. The methodology is based on the statistical analysis of dimensionless performance indices (hydraulic performance indices) derived from a large number of simulations of various water system demand scenarios and/or operating conditions. The hydraulic reliability index is assumed as the probability that, under a given operating condition, the hydraulic performance index will be above a certain threshold. Finally, the system's overall reliability (mechanical + hydraulic) is estimated using the overall reliability index, which is defined by the weighted mean of the hydraulic performance indices obtained for the various operating conditions. A case study using this methodology shows the concrete possibilities of applying this approach to a wide spectrum of cases, and the small influence on overall system reliability normally exerted by such events as the failure of links, pipes, and valves.

The present work describes a procedure for the evaluation of the optimal number, position, configuration, and sizes of detention tanks in urban drainage networks, to decrease the maximum flow depths and velocities for an assigned return period and to comply with the local design requirements. Each candidate solution of the optimization problem is evaluated by means of a semidistributed hydrological model in which the kinematic wave is used as flood routing model, whereas the variational approach is used to evaluate the critical flow characteristics corresponding to a given return period. The procedure, which makes use of a genetic algorithm to search for the optimal solution among the candidates, is applied to a case study drainage network, considering superpipe-based detention tanks as detention systems. The results indicate that these tanks are effective in the rehabilitation of the drainage network and that the cost of this intervention is substantially lower than that corresponding to the upgrading of existing pipes

Water loss is a phenomenon frequently observed within water distribution systems (WDSs), that is considerably worsened by an excessive pressure throughout the network. As an alternative option to pipe replacement, the use of pumps working as turbines, throttle control valves (TCVs), or pressure reduction valves (PRVs) can be used to reduce leakage. For a preassigned number of these devices, their positions and settings can be chosen to minimize the water losses in the network or to minimise the costs associated with the leakage. On the other hand, for a preassigned reduction in leakage, the number, the position and the setting of valves could be optimized in order to minimize their installation and maintenance costs. Based on these observations, a procedure for the optimal choice of the number, position and setting of PRVs is devised. The procedure is aimed at reducing the whole cost associated with water loss in urban WDSs, due to the background leakage from joints, and the purchase, installation and maintaining of the PRVs themselves. The effectiveness of the procedure, which is based on the physical modelling of leakage from pipe joints as well as on the use of a genetic algorithm, is proven using a small but realistic example.