Advances in Engineering Software 89 (2015) 108–113 Contents lists available at ScienceDirect Advances in Engineering Software journal homepage: www.elsevier.com/locate/advengsoft Real-time demands and calibration of water distribution systems A. Vassiljev a,* , M. Koor b , T. Koppel a a Tallinn University of Technology, Tallinn, Estonia b Tallinn Water Company, Tallinn, Estonia article info Article history: Available online 15 July 2015 Keywords: Water distribution system Real-time demands Calibration Optimisation Demand time pattern Demands uncertainty abstract All computer models of water distribution systems (WDS) have to contain information about demands. Usu- ally demands are derived based on customer’s water meters weekly or monthly readings. It gives informa- tion only about the average demand. Dynamics of hourly, daily and weekly demands are usually estimated based on typical demand patterns of different type of consumer groups like domestic households, hospi- tals or hotels. Estimation of demand dynamics by this manner inevitably decreases precision of calibration. Calculations show that differences between real-time and typical demand can influence results of calibra- tion. The paper proposes some methods to minimize this influence. Special software has been developed for estimation of real-time water demands in a WDS. Algorithms and software checked on an operational WDS. © 2015 Civil-Comp Ltd. and Elsevier Ltd. All rights reserved. 1. Introduction Computer models of water distribution systems (WDS) contain information on demands. Summarised water consumption is usually measured for quite long periods (e.g. month) that gives information only on the average base demand. Dynamics of these demands are obtained based on typical dynamic patterns for different type of consumer groups. These consumption patterns are used because of lack of detailed information. Results may differ from actual demands in time (e.g. during different weekdays) and in location of demand (e.g. because of different daily movement of the residents at different parts of the region). Great differences between typical and actual de- mand patterns have been indicated in [2,3]. Thus base demands and corresponding patterns contain large uncertainties which decrease precision of calibration of model. Calibration of computer model is necessary to achieve as near real-life representation of actual WDS as possible. Because of the corrosion and deposition processes, which occur over time after the pipes have been installed, the pipes roughness and diameters changes. Using of good calibrated model is an example very important for estimation of propagation rate of the contaminated zones in case of deliberate or accidental chemical or biological threats. This task may be accomplished only on the basis of WDS model calibrated with good precision [4]. This constraint is especially important in the light of necessity to improve drinking water security management in large cities in EU [5]. The aim of this investigation was to make an effort to decrease errors of calibration. Quality of calibration depends on number of reasons. One of them is * Corresponding author. Tel.: +37258136243. E-mail address: anatoli.vassiljev@ttu.ee (A. Vassiljev). difference between actual and typical demands. Correct estimation of the water consumption and demand pattern at demand nodes is rather difficult [6]. This information is significant for calibration [7] and for further use of the model [8]. Therefore quite detailed measurements were accomplished in one of the District Metered Area (DMA) of WDS of Tallinn. Calculations showed that differences between actual and typical demands influence results of calibration even in area that consists mainly of residential consumers. Other aim was to obtain and analyse differences in actual water demands and demands obtained based on typical demand patterns. Estimation of the actual demands is formulated as optimisation task, which minimizes differences between measured and modelled pres- sures and water flow. All calculations have been accomplished using measurements executed in operational WDS in the year 2012. Special software has been developed for estimation of actual water demands in a WDS. The software is based on the TOOLKIT developed for the EPANET2 [9]. Subroutines were developed and programmed in Visual Basic and in Visual C++. Multiple processors are used simultaneously in order to decrease computational time. Current paper is based upon Vassiljev and Koppel paper [1], but text has been rewritten and ad- ditional analysis of relationships between head losses and water in- flows is added. 2. Analysis 2.1. Brief description of WDS, measurements and variants of calibration All calculations are accomplished using the results of measure- ments taken in the part of WDS of the city of Tallinn in 2012. This part of WDS has one water source and contains from ca 2000 pipes that serve about 1000 consumers. Overwhelming majority of pipes http://dx.doi.org/10.1016/j.advengsoft.2015.06.012 0965-9978/© 2015 Civil-Comp Ltd. and Elsevier Ltd. All rights reserved.