Water Distribution Network Models Research Articles

Accounting for Directional Devices in WDN Modeling

AbstractThis work presents a modification to steady-state water distribution network (WDN) simulation models to account for directional devices such as check valves (CHVs) and flow-control valves (FCVs). These devices, allowing water flow control in a definite direction, are important to manage the hydraulic system functioning over time by considering the variation of some boundary conditions (e.g., required demands and tank levels). However, the simulation models are built on the assumption that water can flow in both directions of each pipe in the hydraulic system, and the information on directionality of some devices is not automatically allowed. Thus, in WDN models, those devices are currently modeled using a heuristic approach intermixed with solving the problem of steady-state WDN analysis. For this reason, a different approach using content and cocontent theory was recently proposed to define the conditions that guarantee the existence and uniqueness of the solution. The alternative proposed in thi...

WaterNetGen: an EPANET extension for automatic water distribution network models generation and pipe sizing

This paper focuses on the generation of synthetic models of water distribution networks (WDN). Models are widely used in many fields related with WDN planning and operation. Therefore, the main contribution of this work is to provide an automatic procedure to build models with the well-known EPANET tool in a manner that, with a small amount of input data and a few clicks, the user can build a network topology and assign suitable pipe diameters. For that purpose, a new application, called WaterNetGen, was designed and implemented as an extension to the EPANET software. WaterNetGen can be used to generate synthetic models of WDN, with several hundred nodes and pipes, within a few minutes. The sizing capability allows the selection of commercial diameters, such that the final network design satisfies certain user-defined design constraints, like minimum diameter, maximum velocity and minimum pressure. The total water demand is allocated to the pipes taking into account their length and a demand coefficient. The water demand of each pipe is then assigned to its start and end nodes and follows a specific demand pattern.

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.

Equivalent hydraulic resistance to simulate pipes subject to diffuse outflows

In water distribution network simulation models, pipes subject to diffuse outflow, either due to connections or to distributed demand or to leaks along their length, are generally converted into pipe elements only subject to lumped demand at their ending nodes. This approximation, which disregards the flow variation along the pipes, generates a loss of axial momentum, which is not correctly taken into account in the present generation of water distribution network models. In this paper a correction to the lumped demand approximation is provided and this equivalence is analyzed within the framework of the Global Gradient Algorithm. This is obtained through a correction of the pipe hydraulic resistance; this approach has proven to be more effective than the use of an asymmetrical lumped demand of the total distributed outflow at the pipe ending nodes. In order to assess the effect of the introduced correction, an application to a simple water distribution system is finally provided.

Estimation of the benefits yielded by pressure management in water distribution systems

The occurrence of water losses in Water Distribution Systems is inevitable. Knowing that most of the real losses take place in distribution mains and in service connections, the methodology proposed in this paper is based on several leakage-assessment approaches from literature and on water distribution network modeling. This allows assessment of the benefits that can be achieved by pressure management in Water Distribution Systems, particularly in terms of water production reduction. Moreover, this approach can be useful for cost benefit analysis to help establish the level after which there is no more economic interest in reducing water losses (Economic Level of Leakage). Finally, the results from hypothetical case studies are presented and discussed, assuming the installation of Pressure Reducing Valves at District Metered Areas entry points.

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.

Online modelling of water distribution systems: a UK case study

Abstract. Hydraulic simulation models of water distribution networks are routinely used for operational investigations and network design purposes. However, their full potential is often never realised because, in the majority of cases, they have been calibrated with data collected manually from the field during a single historic time period and, as such, reflect the network operational conditions that were prevalent at that time, and they are then applied as part of a reactive, desktop investigation. In order to use a hydraulic model to assist proactive distribution network management its element asset information must be up to date and it should be able to access current network information to drive simulations. Historically this advance has been restricted by the high cost of collecting and transferring the necessary field measurements. However, recent innovation and cost reductions associated with data transfer is resulting in collection of data from increasing numbers of sensors in water supply systems, and automatic transfer of the data to point of use. This means engineers potentially have access to a constant stream of current network data that enables a new era of "on-line" modelling that can be used to continually assess standards of service compliance for pressure and reduce the impact of network events, such as mains bursts, on customers. A case study is presented here that shows how an online modelling system can give timely warning of changes from normal network operation, providing capacity to minimise customer impact.

Pressure sensor distribution for leak detection in Barcelona water distribution network

This paper proposes a leakage detection method based on detecting significant discrepancies between pressure measurements and their estimations obtained from the simulation of a calibrated water distribution network model. Every sensor in the network will allow to detect a discrepancy in pressure due to leakage depending on its location. Then, a set of well distributed pressure sensors will generate a leakage signature that allows leakage localisation. This paper presents the methodology used in the Barcelona network for distributing properly the sensors for a good discrimination in the leakage localisation process. The methodology for sensor placement uses the pressure sensitivity matrix to the leakage presence. This matrix is normalised and binarised in order to be used as a leakage signature matrix using the standard model based fault diagnosis approach. Sensors may be installed in any node and leakages are simulated as a constant demand that can appear in any node too. The problem of deciding which are the best localisations for a small number of sensors in order to detect and localise leakages is an inverse problem that should be solved using optimisation. The resulting optimisation problem is of discrete nature and very huge for a real network. This type of problem is, in general, hard to solve and very time consuming. The use of GA (Genetic Algorithms) has been proved adequate according to the formulation of the signatures in the sensitivity matrix.

Developing a modeling tool for flow profiling in irrigation distribution networks

Efforts are underway to rehabilitate the irrigation districts, such as in the Rio Grande Basin in Texas. Water distribution network models are needed to help prioritize and analyze various rehabilitation options, as well as to scientifically quantify irrigation water demands, usages, and losses, and to help manage gate automation. However, commercially available software packages were limited in applications due to their high cost and operational difficulty. This study aims to develop a modeling tool for modeling the water flow profile in irrigation distribution networks. The goal of developing the modeling tool was to make the modeling process simple, fast, reliable and accurate. On the basis of methodological study, the modeling tool has been developed for branching canal networks with the assumption of steady gradually varied flow. The flow profile calculation of the tool was verified from a single channel with 1% root mean squared error compared to the benchmark calculation and a branching network with 5% to 12% relative errors compared to check point measurement along the network. The developed modeling tool will be able to play an important role in water quantification for planning, analysis and development for modernization of irrigation systems. Keywords: irrigation distribution network, modeling tool, flow profiling DOI: 10.3965/j.issn.1934-6344.2009.03.017-026 Citation: Yanbo Huang, Guy Fipps. Developing a modeling tool for flow profiling in irrigation distribution networks.Int J Agric & Biol Eng, 2009; 2(3): 17

Parameter Estimation in Water Distribution Networks

Estimation of pipe roughness coefficients is an important task to be carried out before any water distribution network model is used for online applications such as monitoring and control. In this study, a combined state and parameter estimation model for water distribution networks is presented. Typically, estimation of roughness coefficient for each individual pipe is not possible due to non-availability of sufficient number of measurements. In order to address this problem, a formal procedure based on K-means clustering algorithm is proposed for grouping the pipes which are likely to have the same roughness characteristics. Also, graph-theoretic concepts are used to reduce the dimensionality of the problem and thereby achieve significant computational efficiency. The performance of the proposed model is demonstrated on a realistic urban water distribution network.

Uncertainty reduction in water distribution network modelling using system inflow data

In water distribution network (WDN) modelling, nodal demand is the sum of flows taken by users associated with a computational node. User demands are not fixed in time; rather they are stochastic. Hence, nodal demand is a model parameter with high uncertainty, which is propagated throughout the WDN model, thus also rendering the output values (node pressures and pipe discharges) uncertain. Total water inflow into the network can be accurately measured using flow meters. This paper investigates how knowledge of system inflow can be used as a constraint in WDN modelling, taking into consideration the uncertain nodal demands, and consequently reducing the uncertainty of the model output. Fuzzy sets were used to represent the uncertain demands and modified genetic algorithms were used to find the optimal solutions. As a test case, a set of data from a real WDN was used. The uncertainty of the WDN model output was computed for two cases: first, with the total network inflow taken into consideration; and second, with the inflow used as a constraint. Although the methodology that handles the constraints needs significantly greater computational effort, its results provide a more realistic insight into model uncertainty. The proposed methodology was verified using Monte Carlo simulation.

Using the WCM for transient modeling of water distribution networks

Recent water quality studies have emphasized the need for transient analysis of large pipe networks to properly assess the potential level of intrusion associated with negative pressure and the resulting effect on disinfectant residual efficiency. Transient analysis is computationally demanding even for simple pipe systems, and the computational effort for large pipe networks can be substantially high. Moreover, computational effort and accuracy of solution are interdependent. Therefore, understanding the computational efficiency and the accuracy of solution associated with the available transient analysis methods is essential for efficient handling of transients in large pipe distribution networks. This research investigated the numerical accuracy of solution and the computational efficiency of two popular methods for transient analysis—the wave characteristic method (WCM) and the method of characteristics—and elucidated their implications for practical applications. The authors offer a guideline for selecting the number of friction orifices for the WCM. In addition, this research demonstrated the superior performance of the WCM in both numerical accuracy of solution and computational effort for transient analysis of large water distribution networks.

Water distribution network modelling of a small community using watercad simulator

In this study a network model was constructed for the hydraulic analysis and design of a small community (Sakwa) water distribution network in North Eastern geopolitical region of Nigeria using WaterCAD simulator. The analysis included a review of pressures, velocities and head loss gradients under steady state average day demand, maximum day demand conditions, and fire flow under maximum day demand using average day demand of 60 lpcd.The results indicate: that the tower height of the existing storage tank is inadequate and should be increased from 10m to 15m to provide satisfactory service, and that there are no areas of concern with respect to pressure or available fire flow for the proposed service area and also that flow velocities are not excessive while head loss gradients in the network are within acceptable limits. Pipes P-6, P-12, P-15 and P-19 expectedly have relatively low flow velocities due to the low average day demands in small communities and the constraint of minimum commercially available pipe sizes makes design of self cleansing networks in such communities not easily realizable.

A Variable Rate Coefficient Chlorine Decay Model

Chlorine is the most widely used water disinfectant in the world. As a result, optimal chlorine usage is essential for both human and environmental health. Chlorine decay models can be used to predict residual concentrations in water distribution networks and optimize chlorine dosing. However, the coefficients of current chlorine decay models are often dependent on the loading conditions and are therefore impractical for day-to-day water distribution network modeling purposes and chlorine dosing optimization studies. This study proposes and assesses a novel numerical chlorine decay model with four parameters that are independent of the loading conditions for a given water sample. The model is based on kinetic equations derived from the rate law for concurrent bimolecular second order reactions with chlorine and will be referred to as the variable rate coefficient (VRC) chlorine decay model. The performance of the proposed model is compared with another model reported in the literature, and the VRC model is also assessed for reliability with data sets that are omitted during model calibration. The VRC model is consistently found to be in agreement with the experimental data.

Cost-effective leakage reduction through district metering

A new stochastic water distribution network (WDN) modelling tool has been developed with the aim of providing a sound basis for cost-effective strategic planning of WDN monitoring schemes in terms of quantifiable leakage. Through an analysis of uncertainties in water demand and its propagation through a WDN, the developed computer tool recommends the most cost-effective solution in terms of the number and location of monitoring sites necessary to increase the probability of identifying the location of leaks (or other system anomalies). The methodology was tested on a medium-sized WDN in the UK and the results are presented in this paper.

Evaluating the potential of biofilm control in water supply systems by removal of phosphorus from drinking water

Effect of microbially available phosphorus (MAP) on biofilm development in drinking water systems was investigated at the pilot-scale experiments over 3 years. Completely mixed biofilm reactors Propella (water detention time 24 h, flow rate 0.25 m s(-1), PVC pipe coupons) were used as water distribution network models. Four experimental runs were carried out with water containing different levels of phosphorus which was limiting nutrient for bacterial growth. Positive correlation between MAP in the inlet water and heterotrophic plate count (correlation coefficient 0.95) in biofilm, as well as for the total bacteria number (correlation coefficient 0.71), was observed. However, our experiments showed that removal of phosphorus down to very low levels (below detection limits of chemical method and MAP < 1 microg L(-1) was not an efficient strategy to eliminate bacterial regrowth and biofilm formation (< 51,00,000 cells/cm2) in drinking water supply systems.

Adjusting Nodal Demands in SCADA Constrained Real-Time Water Distribution Network Models

This paper describes the proportional demand method and the target demand method, two techniques for adjusting estimated demands in hydraulic models of water distribution networks to produce solutions that are consistent with available supervisory control and data acquisition (SCADA) data. The two techniques assume that pipe resistances and SCADA data are accurate and that the combination of SCADA data and demand estimates produce overdetermined problems. Nodal demands are regarded as stochastic variables which fluctuate about an estimated mean value. The method of weighted least squares is used to obtain solutions that satisfy all of the constraints imposed by SCADA data with adjusted nodal demands that most closely resemble the estimates. The methods are intended for use in real-time modeling but are limited to quasi-steady state flow. The paper demonstrates the methods on two example problems.

GISRed 1.0, a GIS-based Tool for Water Distribution Models for Master Plans

GISRed is a customized extension to ArcView® GIS3.2, oriented to modeling and calibration of water distribution networks, and which integrates all capabilities…

Stochastic Model to Evaluate Residential Water Demands

The analysis and modeling of water distribution networks has been a well established engineering field for many years. However, important questions remain concerning the correct assessment of the spatial and temporal distribution of network user demands. To contribute to better knowledge and understanding of consumption patterns in an urban network, a stochastic model for residential water demand simulation is developed. The model is based on a rectangular pulse point process of residential consumption of given duration and intensity. Both variables are considered as statistically independent variables, with a nonhomogeneous point process used to describe pulse occurrences over time. The model includes a total of nine free parameters that define five different statistical functions. The parameters were calibrated from known demands in residential areas located in Milford, Ohio, and in Valencia, Spain. The model is also applied to the simulation of longer periods, with satisfactory agreement generally found between synthetic and historical series for most significant variables used in practical applications.

Modelling of demand and losses in real-life water distribution systems

Despite the rapid development of modelling methods in the water industry, some problems of water distribution network modelling are still unresolved, such as how to represent adequately real demand and losses. Both are dependent upon service pressure, yet the relationship is not fully known. The paper discusses various proposals and shows how the modelling procedure could be improved – if that relationship were known. A case from practice is included for illustration. It describes how a real emergency was analysed on the model with the help of the local staff and using past experience. A few suggestions for further work are included at the end of the paper.