Water distribution network calibration using enhanced GGA and topological analysis

The calibration of hydraulic models of water distribution networks (WDN) is of preeminent importance for their analysis and management. It is usually achieved by solving a constrained optimization problem based on some priors on decision variables and the demand-driven simulation of the entire network, given the observations of some hydraulic status variables (i.e. typically nodal heads and sometimes pipe flows). This paper presents a framework to perform the calibration of pipe hydraulic resistances considering two main issues: (i) the enhancements of WDN simulation models allowing us to simplify network topology with respect to serial nodes/trunks and/or to account for a more realistic representation of distributed demands and (ii) a different formulation of the calibration problem itself. Depending on the available measurements, the proposed calibration strategy reduces the hydraulic simulation model size and can permit the decomposition of the network. On the one hand, such a procedure allows for numerical and computational advantages, especially for large size networks. On the other hand, it allows a prompt analysis of observability of calibration decision variables based on actual observations and might help identifying those pipes (i.e. hydraulic resistances) which are more important for the whole network behaviour

Calibration of Design Models for Leakage Management of Water Distribution Networks

AbstractWater losses in urban water distribution networks (WDN) accelerate the deterioration of such infrastructures. The enhanced hydraulic modelling provides a phenomenological representation of WDN hydraulics, including the modelling of leakages as function of pipe average pressure and deterioration. The methodological use of such models on real WDN was demonstrated to support the planning of leakage management actions. Nonetheless, many water utilities are still in the process of designing flow/pressure monitoring, thus data available are not enough to perform detailed calibration of such models.This work presents a physically based approach for the calibration of WDN hydraulic models aimed at supporting leakage management plans since early stages. The proposed procedure leverages the key role of mass balance in enhanced hydraulic models and the technical insight on pipe deterioration mechanisms for various quantity and quality of available data. Two calibration studies of real WDNs demonstrate the feasibility of the approach and show that the distribution of leakages in the WDN does not much influence the pressure values, which confirms the need for flow measurements at monitoring districts for leakage and asset management

Editorial: Water and environmental challenges in a changing world: the perspective of the 13th International Conference on Hydroinformatics HIC 2018

n/

General metrics for segmenting infrastructure networks

The classic modularity index for community detection in complex networks was recently tailored to water distribution networks (WDNs) and extended in order to be cut-position sensitive. Next, the WDN-oriented modularity index was enhanced in order to overcome the resolution limit of the classic modularity. Nonetheless, the modularity-based metrics developed so far allow the networks to be segmented into modules/segments that are similar to each other according to specific pipe characteristics (e.g., pipe lengths, distributed demand, background leakages, etc.). The present work extends and proves the strategy to overcome the resolution limits focusing on an infrastructure index that drives WDN segmentation toward modules that are internally similar with respect to given attributes (e.g., pipe diameters, average pipe pressures, average pipe elevations, etc.), since this aim is suitable for several practical purposes. The introduction of the attribute-based infrastructure index permits a comprehensive discussion and comparison of the metrics for infrastructure network segmentation through simple examples. Finally, the practical implications of increasing the resolution of internally similar modules are demonstrated on a well-known benchmark WDN considering various pipe attributes

WDNetXL: Efficient Research Transfer For Management, Planning And Design Of Water Distribution Networks

The WDNetXL system (www.hydroinformatics.it) is aimed at promoting transfer of research achievements in water distribution network (WDN) analysis, planning and management to practitioners, students and researchers. In order to facilitate the technology transfer, the WDNetXL functions are integrated into the worldwide known MS-Excel data-management environment. Advanced hydraulic modeling and topological analyses of WDN are combined with efficient optimization strategies to make readily available the latest, even customized, decision support tools for planning and management of WDNs. All these features make WDNetXL of practical support for technicians as well as a privileged platform to test innovations coming from research in WDN analysis, planning and management area. This, contribution illustrates the WDNetXL research transfer paradigm and its architecture, providing also few details about the main advancements in WDN analysis, which represents the primary support for engineers’ activities and the base component for other functions

Generalizing WDN simulation models to variable tank levels

In water distribution network (WDN) steady-state modelling, tanks and reservoirs are modelled as nodes with known heads. As a result, the tank levels are upgraded after every steady-state simulation (snapshot) using external mass balance equations in extended period simulation (EPS). This approach can give rise to numerical instabilities, especially when tanks are in close proximity. In order to obtain a stable EPS model, an unsteady formulation of the WDN model has recently introduced. This work presents an extension of the steady-state WDN model, both for demand-driven and pressure-driven analyses, allowing the direct prediction of head variation of tank nodes with respect to an initial state. Head variations at those nodes are introduced as internal unknowns in the model, the variation of tank levels can be analyzed in the single steady-state simulation and EPS can be performed as a sequence of simulations without the need for external mass balances. The extension of mass balance at tank nodes allows the analysis of some technically relevant demand components. Furthermore, inlet and outlet head losses at tank nodes are introduced and large cross-sectional tank areas are allowed by the model and reservoirs become a special case of tanks. The solution algorithm is the generalized-global gradient algorithm (G-GGA), although the proposed WDN model generalization is universal

Some explicit formulations of Colebrook-White friction factor considering accuracy vs. computational speed

The Colebrook–White formulation of the friction factor is implicit and requires some iterations to be solved given a correct initial search value and a target accuracy. Some new explicit formulations to efficiently calculate the Colebrook–White friction factor are presented herein. The aim of this investigation is twofold: (i) to preserve the accuracy of estimates while (ii) reducing the computational burden (i.e. speed). On the one hand, the computational effectiveness is important when the intensive calculation of the friction factor (e.g. large-size water distribution networks (WDN) in optimization problems, flooding software, etc.) is required together with its derivative. On the other hand, the accuracy of the developing formula should be realistically chosen considering the remaining uncertainties surrounding the model where the friction factor is used. In the following, three strategies for friction factor mapping are proposed which were achieved by using the Evolutionary Polynomial Regression (EPR). The result is the encapsulation of some pieces of the friction factor implicit formulae within pseudo-polynomial structures

Development of pipe deterioration models for water distribution systems using EPR

The economic and social costs of pipe failures in water and wastewater systems are increasing, putting pressure on utility managers to develop annual replacement plans for critical pipes that balance investment with expected benefits in a risk-based management context. In addition to the need for a strategy for solving such a multi-objective problem, analysts and water system managers need reliable and robust failure models for assessing network performance. In particular, they are interested in assessing a conduit's propensity to fail and how to assign criticality to an individual pipe segment. In this paper, pipe deterioration is modelled using Evolutionary Polynomial Regression. This data-driven technique yields symbolic formulae that are intuitive and easily understandable by practitioners. The case study involves a water quality zone within a distribution system and entails the collection of historical data to develop network performance indicators. Finally, an approach for incorporating such indicators into a decision support system for pipe rehabilitation/replacement planning is introduced and articulated

Data-mining approach to investigate sedimentation features in combined sewer overflows

Sedimentation is the most common and effectively practiced method of urban drainage control in terms of operating installations and duration of service. Assessing the percentage of suspended solids removed after a given detention time is essential for both design and management purposes. In previous experimental studies by some of the authors, the expression of iso-removal curves (i.e. representing the water depth where a given percentage of suspended solids is removed after a given detention time in a sedimentation column) has been demonstrated to depend on two parameters which describe particle settling velocity and flocculation factor. This study proposes an investigation of the influence of some hydrological and pollutant aggregate information of the sampled events on both parameters. The Multi-Objective (EPR-MOGA) and Multi-Case Strategy (MCS-EPR) variants of the Evolutionary Polynomial Regression (EPR) are originally used as data-mining strategies. Results are proved to be consistent with previous findings in the field and some indications are drawn for relevant practical applicability and future studies

Optimal Design of District Metering Areas

Abstract The search for optimal segmentations aimed at defining district metering areas (DMAs) is a challenging and crucial issue in the analysis, planning and management of water distribution networks (WDNs). The need to select optimal segmentations relates to a number of important technical reasons. Today, the most relevant one is the leakage management by means of pressure-control zones. This contribution proposes a novel two-steps strategy for DMAs planning. The strategy is based on the segmentation design as first step, to achieve a scenario of optimal locations of "conceptual cuts"; during the second step, these are the candidate for the location of (closed) gate valves or flow measurement devices that gave rise to district monitoring areas (DMAs). The segmentation step is performed solving a multi-objective optimization problem (i.e. WDN-oriented modularity maximization versus the number of "conceptual cuts" minimization). The second step accomplishes the real DMAs design by solving a three-objective optimization, i.e. the minimization of the background leakages versus the unsupplied customers demand versus the flow observations. This means that the procedure will search for a set of scenarios having a number of closed gate valves installed at the "conceptual cuts" that do not decrease the WDN hydraulic capacity below that necessary for a sufficient service to customers, while contemporarily reducing the background leakages. A pressure-driven modelling approach is used to predict background leakage reduction and the unsupplied customers demand. The procedure is explained on a benchmark network from literature, the Apulian network