Schedule management in intermittent water supply systems using multi-criteria optimization

Autores UPV
CONGRESO Schedule management in intermittent water supply systems using multi-criteria optimization


Intermittent water supply (IWS) is the way millions of people worldwide have access to water currently (van der Berg and Danilenko, 2011). Some researchers suggest that the increasing water scarcity, due to the climate change, and the increasing demand, due to the upsurge in population, may lead to a more frequent use of intermittent supply. It is considered IWS when the supply of the service is performed for a limited amount of time. The frequency with which water is generally supplied is daily, although in extreme cases it reaches more than one day. In many small towns with IWS, the service is performed for several hours for the entire network, without differentiating sectors; in larger cities supply is performed by means of sectors having different delivery schedules. There is abundant literature on planning, design, operation and maintenance of systems with continuous supply. However, the operation of IWS systems is mainly based on personnel experience and simple water supply and demand tradeoff analyses. Due to the limited amount of hours of supply and the establishment of delivery schedules with little technical criteria, the peak factor increases to values up to 4-6 and, consequently, much larger flowrates are delivered in the peak hours with respect to what is normal in continuous systems. This implies greater storage volume and larger diameters in the network to meet the hydraulic and the demand requirements. Several studies show that intermittent systems produce insufficient pressure in unfavorable areas or sectors, thus generating dissatisfaction and complaints among users. This paper proposes a tool for the technical management of IWS systems, a methodology to manage supply schedules for every sector of the network, to improve the conditions of service based on multi-criteria optimization. The objective is to reduce the peak flow produced by the simultaneous supply of sectors, by optimally assigning delivery schedules based on quantitative and qualitative technical criteria. In addition to engineering variables, the technical expertise of the personnel of the water supply company is incorporated into the optimization process through their opinion, using Analytic Hierarchy Process (AHP) as multi-criteria decision technique. The case study corresponds to one of the subsystems of the water supply system of the city of Oruro (Bolivia), consisting of 15 sectors fed by a single tank.