Preliminary estimation of spatial and temporal synchronization of water demands in the capital city of Libya

Water supply systems represent an essential component of the infrastructure in urban populations worldwide. Water distribution systems are designed by sizing system components so that they meet current and future demands to be provided at minimum required levels of water pressure and quality. The cost of establishing newly-designed water supply systems is largely dedicated to the supply and placement of pipelines. The sizing of pipelines is highly dependent on the amount of water demands allocated to distribution nodes of the system under consideration. The current demand allocation practices normally imply that there is perfect spatial synchronization among the aggregated demands, which is not essentially the case in practice. This assumption indicates that most users follow a single diurnal pattern, which means that such users react simultaneously and in exactly the same way during normal and peak demand conditions. However, the way users react in real-world systems highly depends on many factors that differ from one user to another such as social habits and financial constraints. Recent studies anticipated that low levels of spatial demand synchronization can result in significant savings of the capital cost of water supply systems. In this paper, an investigation on the actual demand spatial synchronization is carried out using field measurements of diurnal demand patterns for different users in a residential area located in the city of Tripoli. Results showed that users react independently and the correlation is far away from the perfect case. The impacts of the spatial synchronization of water demands on the hydraulic performance and cost of water distribution networks have been studied by a number of researchers. A chance-constrained optimization model applied to a simple network (Tolson et al. 2004) showed that, for a fixed level of hydraulic reliability, network cost increases with the level of spatial synchronization between demands. Additionally, the study pointed out that a higher level of cross correlation between network demands has the effect of producing larger fluctuations in nodal pressure accompanied with more frequent low-pressure failures. A multi-objective evaluation models were tested on the New York tunnels problem under synchronized demands confirming that network cost increases with level of demand synchronization when fixing level of hydraulic reliability (Kapelan et al. 2005; Babayan et al. 2005). A systematic synchronization analysis was conducted to gain a better understanding of the relationship between synchronized demands, network cost, and hydraulic performance (Filion et al. 2006). The results of these studies showed that, in systems without tank storage, the level of synchronization between nodal demands is proportional to variability of nodal pressures. The aim of this paper is to investigate the level of spatial synchronization of water demands in a real system, namely in the capital city of Libya. The results of the study pointed out that the level of synchronization is not strong and a demand analysis should be carried out to accurately model network for better hydraulic performance and to achieve more cost-effective designs