Probabilistic Minimum Night Flow Estimation in Water Distribution Networks and Comparison with the Water Balance Approach: Large-Scale Application to the City Center of Patras in Western Greece

Athanasios V Serafeim,Irene Karathanasi,Andreas Langousis,Roberto Deidda,George Kokosalakis

doi:10.3390/w14010098

Athanasios V Serafeim, Irene Karathanasi + Show 3 more

Open Access

https://doi.org/10.3390/w14010098

Copy DOI

Abstract

Quantification of water losses (WL) in water distribution networks (WDNs) is a crucial task towards the development of proper strategies to reduce them. Currently, WL estimation methods rely on semi-empirical assumptions and different implementation strategies that increase the uncertainty of the obtained estimates. In this work, we compare the effectiveness and robustness of two widely applied WL estimation approaches found in the international literature: (a) the water balance, or top-down, approach introduced by the International Water Association (IWA), and (b) the bottom-up or minimum night flow (MNF) approach, based on a recently proposed probabilistic MNF estimation method. In doing so, we use users’ consumption and flow-pressure data from the 4 largest pressure management areas (PMAs) of the WDN of the city of Patras (the third largest city in Greece), which consist of more than 200 km of pipeline, cover the entire city center of Patras, and serve approximately 58,000 consumers. The obtained results show that: (a) when MNF estimation is done in a rigorous statistical setting from high resolution flow-pressure timeseries, and (b) there is sufficient understanding of the consumption types and patterns during day and night hours, the two approaches effectively converge, allowing for more reliable estimation of the individual WL components. In addition, when high resolution flow-pressure timeseries are available at the inlets of PMAs, the suggested version of the bottom-up approach with probabilistic estimation of MNF should be preferred as less sensitive, while allowing for confidence interval estimation of the individual components of water losses and development of proper strategies to reduce them.

Highlights

In the two subsections, we briefly describe the water balance approach introduced by International Water Association (IWA), and the bottom-up approach based on minimum night flow (MNF) estimates obtained by applying the probabilistic approach of Serafeim et al [42], in order to estimate the water losses (WL) in water distribution networks (WDNs) and their decomposition into real losses (RL) and apparent losses (AL)
The bottom-up approach is affected by MNF estimation uncertainties originating mostly from the quality and resolution of the available flow-pressure timeseries, the estimation method applied to extract flow minima, as well as the representativeness of the assumed users’ night consumption (UNC)
In an effort to improve the accuracy and robustness of the bottom-up approach, Serafeim et al [42] developed a probabilistic framework for MNF estimation in WDNs, based on statistical metrics, that filters out noise effects, estimating MNF as the average flow of the most probable states during the night hours of the low-consumption period of the year

Summary

Introduction

All water distribution networks (WDNs), regardless of their age and construction materials, exhibit water losses (WL). The latter are defined as the difference between the total volume of water entering a WDN in a given period of time (system input volume, SIV), and the authorized consumption (AC), and are divided into apparent and real losses. Apparent losses (AL) occur due to unauthorized consumption (UC) by illegal connections on the main WDN, metering errors at the inlets of district metered areas (DMAs) or pressure management areas (PMAs), and incorrect estimates of billed users’ consumptions. Real losses (RL) correspond to the lost water due to leakage through the pipeline connections, pipe cracks or breaks, as well as overflows in tanks and pressure wells [1,2]

Objectives

Methods

Results

Conclusion