Pressure-deficient Conditions Research Articles

Effect of variation of empirical exponent coefficient values in water distribution network analysis

The water distribution network supplies water to consumer to fulfill demands at desired pressure. Due to pressure deficient conditions pressure fall below minimum required which ultimately lead to reduction in flow supplied to consumer. The water distribution network is said to be pressure deficient, if the pressure head in each node is less than the required head. Adding artificial element approach for predicting partial flow at demand node in pressure deficient condition is used by many researchers. The objective of study is to investigate effect of variation in empirical exponent coefficient on emitter exponent, pressure and actual demand at demand node. The steady state simulation is carried out for case study network with pressure deficient node as emitter node using Fictitious component free – Pressure Deficient Network Algorithm. The emitter coefficient formula, derived from Wagner’s equation is used for predicting actual demand under pressure deficient condition. The value of emitter coefficient depends on emitter exponent coefficient value, which is calculated using empirical exponent coefficient. The study is carried out for three different values of empirical exponent coefficient 0.5, 1, 1.5, 1.852, 2 and 2.5 respectively. The simulation analysis shows that as empirical exponent increases emitter exponent decreases, pressure decreases and actual demand at nodes increases. This study can be useful in calculating resilience index, which is measure of average efficiency of water distribution network under pressure deficient condition.

Review of hydraulic modelling approaches for intermittent water supply systems

Abstract Intermittent water supply (IWS) is widely used around the world, and with the increase in population and predicted future water scarcity, IWS applications seem to continue. While most of the existing studies on water supply concentrate on continuous water supply (CWS), the research focused on the IWS is now becoming mainstream. Hydraulic modelling is an effective tool for the process of planning, design, rehabilitation, and operation of water distribution systems. It helps significantly in engineers’ decision-making processes. The necessity of modelling IWS systems arises from the complexity and variety of problems caused by intermittency. This paper offers a review of the state-of-the-art IWS modelling and identifies the key strengths and limitations of the available approaches, and points at potential research directions. Currently, neither computer software nor a practically used approach is available for modelling IWS. For a rigorous simulation of IWS, system characteristics first need to be understood, i.e., the user behaviour under pressure-deficient conditions, water losses, and filling and emptying processes. Each of them requires further attention and improvement. Additionally, the necessity of real data from IWSs is stressed. Accurate modelling will lead to the development of improved measures for the problems caused by intermittency.

Exploration of Pressure Driven Method in Hydraulic Modelling of Water Distribution Network

Abstract: A water supply network is assessed on its efficiency and capability to cater to the demand of consumers. There are two approaches for analysing a network viz. Demand Driven Approach (DDA) & Pressure Driven Approach (PDA). It assumes that the demands at all nodes are always satisfied, irrespective of the available nodal pressure. But many a times, in an operational network, certain situations such as pipe burst, pump failure, fire demand, supply shortage etc. arise. These situations cause pressure deficiency or even negative pressures. Such lower pressures cause water shortage at delivery points or sometimes even supply disruption. This is where DDA fails. PDA is comparatively a new approach. But it is capable of simulating pressure deficient conditions and analysing their effects on the network. Though, not for designing, but it can be efficiently used to simulate different conditions, analyse their effects and determine solutions to mitigate hazards. This paper compares DDA & PDA by analysing a looped network.

Control strategies to improve the low water quality of Souk-Ahras city

This work reports control strategies of the water quality in the city of Souk-Ahras (east Algeria). With the recent development, rapid population growth, and the consequences of climate change, the capacity of water supply reserves becomes more unpredictable in the long term. This has drastically affected the distributed water quantity. A correlation between bacteriological water analysis and the analysis of pollution indicative physicochemical parameters is developed to replace the slow bacteriological analysis, which takes more than two days, by directly accessible physicochemical analysis to anticipate the case-onset of waterborne diseases. A good correlation is found between different combinations of physicochemical pollution parameters: (Turbidity, Nitrates); (Turbidity, Active chlorine) (nitrates, active chlorine); (Ammonium, Chlorine) and (Turbidity, Ammonium) with Spearman rank coefficients of 0.8657, -0.8602 and -0.8531 -0.8227 et 0.7957 respectively. Besides, long term analysis (over several years) revealed a high correlation of more than 0.92 between the analysis of pollution indicative physicochemical parameters and bacteriological analysis. The EPANET software is used to simulate the hydraulic behaviour of the network system over an extended period within pressurized and pressure-deficient conditions. The simulation results of several supply scenarios of daily drinking water pressure in the city center area show that 62% of drinking water distribution system is supplied with a steep slope (80 m), 10% with unsatisfactory pressure and only 23% with acceptable pressure (1–80 m).Therefore, the high working pressure at the mesh, and the interruptions of the water supply are factors that can lead to the occurrence of cross-connection cases. This diagnosis of the defects in the water supply system is combined with a statistical data analysis of physicochemical parameters to set up an effective sampling strategy that takes into account the frequency of analysis and the areas at risk to prevent the risk of waterborne diseases.

Fictitious Component Free - Pressure Deficient Network Algorithm for Water Distribution Network with Variable Minimum and Required Pressure-Heads

The pressure-driven analysis is essential for modelling the pressure deficient condition of water distribution networks. Owing to the complexity, the development of pressure-driven analysis algorithms remains a grey area over the past few decades. As a milestone, EPANET 2.0 got upgraded to EPANET 2.2 with the inclusion of pressure-driven analysis. However, EPANET 2.2 has a shortcoming of using only a single value for the parameters, minimum pressure-head and required pressure-head of the demand nodes. Ironically, when a water distribution network serves for a wide area or during a fire-fighting period, the demand nodes have variable values for each of these parameters. To address this, a new method named Fictitious Component Free - Pressure Deficient Network Algorithm (FCF-PDNA) is proposed in this paper. The FCF-PDNA does not require any additional fictitious components. It can be used for both steady-state and extended period simulations. The proposed method is applied to water distribution networks of different sizes and types and confirmed that the FCF-PDNA could deal with variable values of minimum and required pressure-head. The suitability of this method for different scenarios that will lead to pressure deficient conditions is also analysed and verified. Moreover, the computational time taken by the FCF-PDNA and the EPANET 2.2 pressure-driven analysis is similar.

Effects of Non-Zero Minimum Pressure Heads in Non-iterative Application of EPANET 2 in Pressure-Dependent Volume-Driven Analysis of Water Distribution Networks

While analysing a real network, the assumption of zero minimum pressure head as the elevation of demand node may lead to unrealistic results as some residual pressure is necessary to derive any outflow at the node. A more realistic minimum pressure head plays an important role for analysis of an existing or proposed network. The present study extends a novel method of pressure-dependent volume driven-analysis by investigating the effects of realistic minimum pressure heads. The novelty of the proposed method is to evaluate the practical impact of the zero minimum pressure head assumption under pressure-deficient condition in water distribution networks considering pipe isolation, fire demand, and altering total reservoir heads. The results obtained from the present method are compared with the results based on the more optimistic traditional assumption of zero minimum residual pressure-head. It is observed that time to fill the storage tanks under both normal and pressure-deficient conditions for non-zero minimum pressure head is higher. All the simulations were performed using graphical user interface of EPANET 2. Thus, the proposed approach can be used readily by researchers and practitioners without requiring any additional computational codes development.

Partial Recovery of Water Supply in Disaster Using Pressure-Dependent Analysis

Disaster to water supply systems can occur due to failure of its raw water resource. Providing water supply in crisis period is a daunting task for water supply authorities. Flood or earthquake can damage a storage dam that supplies drinking water to a city. If one of the raw water resources, which supplies water to a city, is damaged in the disaster, the system must ensure that it receives water from the alternate raw water resource to maintain continuous water supply for the minimum life sustenance (say, 70 Liters Per Capita per Day, LPCD) by introducing an interlinking pipeline from the adjoining city’s water supply. In conventional water network solving, demand is fixed. It is presumed that the demand is always satisfied at the nodes and the nodal pressures and pipe flows are determined with respect to this known demand. All the traditional network solving algorithms are based on this assumption. When a major raw water resource supplying water to a city fails, pressure-deficient conditions are formed in the distribution system and alternative arrangement must be made to recover water supply. In such situation, the traditional methods are not enough to describe the behavior of pipe network. Therefore, pressure-dependent demand (PDD) analysis is an important tool used for analyzing the networks which are pressure deficient. This paper describes a small hypothetical model that simulates the disaster scenario due to failure of a water storage dam in an event of disaster such as flood. A PDD analysis of such situation has been carried out using WaterGEMS software. The paper also aims to prepare action plans of partial recovery of water supply in such crisis conditions.

Impact of Pressure-Driven Demand on Background Leakage Estimation in Water Supply Networks

Increasing water demand due to urbanization creates a need to develop schemes for managing water supply networks (WSNs). In recent years, hydraulic modeling of WSNs has been used to assess the state of networks in terms of leakage analysis and pressure control. These models are based on demand-driven modeling (DDM) analysis and pressure-driven modeling (PDM) analysis. The former assumes that the nodal demand is fulfilled consistently regardless of the nodal pressure head. The latter appraises the demand as a function of the available pressure head at the nodes. In a previous paper by Adedeji et al. (2017), an algorithm was presented for background leakage detection and estimation in WSNs. The results demonstrated that the algorithm allows the detection of critical pipes and the indication of the nodes where such critical pipes are located for possible pressure control. However, such an algorithm assumes a demand-driven condition of WSNs. In this paper, a pressure-driven modeling is integrated into the developed algorithm with emphasis on its impact on the background leakage estimate. The results obtained are compared to the demand-driven analysis using two WSNs as case studies. The results presented, which consider pipe and node levels, demonstrate that the reliance of the nodal demand on the available pressure head at the node influences the magnitude of the background leakage flow. It is conceived that this investigation might be crucial for the background leakage estimation while considering WSNs operating under pressure-deficient conditions. In this paper, the solution time for both simulation scenarios is also presented.

Using Nodal Infection Risks to Guide Interventions Following Accidental Intrusion due to Sustained Low Pressure Events in a Drinking Water Distribution System

Improving the risk models to include the possible infection risk linked to pathogen intrusion into distribution systems during pressure-deficient conditions (PDCs) is essential. The objective of the present study was to assess the public health impact of accidental intrusion through leakage points in a full-scale water distribution system by coupling a quantitative microbial risk assessment (QMRA) model with water quality calculations based on pressure-driven hydraulic analysis. The impacts on the infection risk of different concentrations of Cryptosporidium in raw sewage (minimum, geometric mean, mean, and maximum) and various durations of intrusion/PDCs (24 h, 10 h, and 1 h) were investigated. For each scenario, 200 runs of Monte Carlo simulations were carried out to assess the uncertainty associated with the consumers’ behavioral variability. By increasing the concentrations of Cryptosporidium in raw sewage from 1 to 560 oocysts/L for a 24-h intrusion, or by increasing the duration of intrusion from 1 to 24 h, with a constant concentration (560 oocysts/L), the simulated number of infected people was increased by 235-fold and 17-fold, respectively. On the first day of the 1-h PDCs/intrusion scenario, a 65% decrease in the number of infected people was observed when supposing no drinking water withdrawals during low-pressure conditions at nodes with low demand available (<5%) compared to no demand. Besides assessing the event risk for an intrusion scenario, defined as four days of observation, the daily number of infected people and nodal risk were also modeled on different days, including during and after intrusion days. The results indicate that, for the case of a 1-h intrusion, delaying the start of the necessary preventive/corrective actions for 5 h after the beginning of the intrusion may result in the infection of up to 71 people.

Analysis of water distribution network under pressure-deficient conditions through emitter setting

Abstract. Pressure-driven analysis (PDA) of water distribution networks necessitates an assessment of the supplying capacity of a network within the minimum and required pressure ranges. Pressure-deficient conditions happen due to the uncertainty of nodal demands, failure of electromechanical components, diversion of water, aging of pipes, permanent increase in the demand at certain supply nodes, fire demand, etc. As the demand-driven analysis (DDA) solves the governing equations without any bound on pressure head, it fails to replicate the real scenario, particularly when the network experiences pressure-deficient situations. Numerous researchers formulated different head–discharge relations and used them iteratively with demand-driven software, while some other approaches solve them by incorporating this relation within the analysis algorithms. Several attempts have been made by adding fictitious network elements like reservoirs, check valves (CVs), flow control valves (FCVs), emitters, dummy nodes and pipes of negligible length (i.e., negligible pressure loss) to assess the supplying capability of a network under pressure-deficient conditions using demand-driven simulation software. This paper illustrates a simple way of assessing the supplying capacity of demand nodes (DNs) under pressure-deficient conditions by assigning the respective emitter coefficient only for those nodes facing a pressure-deficit condition. The proposed method is tested with three benchmark networks, and it is able to simulate the network without addition of any fictitious network elements or changing the source code of the software like EPANET. Though the proposed approach is an iterative one, the computational burden of adding artificial elements in the other methods is avoided and is hence useful for analyzing large networks.

A toolbox for assessing the impacts of cyber-physical attacks on water distribution systems

This work introduces epanetCPA, an open-source MATLAB® toolbox for modelling the hydraulic response of water distribution systems to cyber-physical attacks. epanetCPA allows users to quickly design various attack scenarios and assess their impact via simulation with EPANET, a popular public-domain model for water network analysis. The toolbox offers both demand-driven and pressure-driven simulations, enabling the users to realistically analyze cyber-physical attacks and their impacts under both pressure sufficient and pressure deficient conditions. epanetCPA is available under the MIT license.

Combining a Multispecies Water Quality and Pressure-Driven Hydraulic Analysis to Determine Areas at Risk During Sustained Pressure-Deficient Conditions in a Distribution System

AbstractRealistic numerical models can assist in managing pressure losses in water distribution systems, which is a challenge for water utilities. This paper presents a methodology for simulating t...

Discussion of “Hydraulic Simulation Techniques for Water Distribution Networks to Treat Pressure Deficient Conditions” by Ho Min Lee, Do Guen Yoo, Joong Hoon Kim, and Doosun Kang

Discussion of “Hydraulic Simulation Techniques for Water Distribution Networks to Treat Pressure Deficient Conditions” by Ho Min Lee, Do Guen Yoo, Joong Hoon Kim, and Doosun Kang

Closure to “Hydraulic Simulation Techniques for Water Distribution Networks to Treat Pressure Deficient Conditions” by Ho Min Lee, Do Guen Yoo, Joong Hoon Kim, and Doosun Kang

Closure to “Hydraulic Simulation Techniques for Water Distribution Networks to Treat Pressure Deficient Conditions” by Ho Min Lee, Do Guen Yoo, Joong Hoon Kim, and Doosun Kang

Discussion of “Hydraulic Simulation Techniques for Water Distribution Networks to Treat Pressure Deficient Conditions” by Ho Min Lee, Do Guen Yoo, Joong Hoon Kim, and Doosun Kang

Discussion of “Hydraulic Simulation Techniques for Water Distribution Networks to Treat Pressure Deficient Conditions” by Ho Min Lee, Do Guen Yoo, Joong Hoon Kim, and Doosun Kang

Improved complementary reservoir solution to evaluate nodal outflow under pressure-deficient conditions

Water distribution system supplies water to the consumers as per the designed condition if requirement of water matches with designed level. It seldom matches the designed condition during operation scenario. Uncertainty of the demand, failure of components, diversion of water, aging of pipeline, permanent increase in the demand at certain supply node, fire demand etc. creates deficit in supply. In such situations, it is important to assess actual flow that can be delivered from nodes so that the authority concerned can take up alternate steps to tackle the situation immediately. Though there are several methods available to analyze pipe networks under pressure-deficient conditions, researchers evolve new approaches or improve existing approaches that can be implemented easily with existing software. This paper proposes an improved method for pressure-driven analysis to minimize the number of addition or deletion of complementing reservoirs in complementary reservoir solution approach. Main logic of the improved method is that no supply from a node is possible if the pressure drop at a node exceeds the difference in hydraulic gradient of source and maximum pressure drop node. The proposed method is applied to three benchmark networks and results of the study show that the improved method simplifies the analysis process by reducing number of addition of complementing reservoirs.

Managing Disasters Using Pressure Dependent Demand Analysis – Case Study of Shirpur Town

Water is the most essential component for sustaining lives of humans and other living creatures. Supplying potable water with adequate residual pressure is a fundamental responsibility of city administration, which they do during normal conditions. But sometimes, abnormal conditions are formed resulting pressure deficient conditions during the daily operations of water distribution networks. These are caused due to common occurrences such as pump failure, pipe bursts, and isolation of major pipes from the system for planned maintenance work and excessive firefighting demands. Total water stop conditions may arise, when the major source supplying water to the city fails in natural disaster such as floods, Tsunami, earthquake or manmade disaster such as terrorist attack. Unlike the pipe failure, longer time is required for restoring water in case of source failure condition. In such situations, the quantity of water is generally decreased and the water distribution systems (WDS) may not be able to satisfy all consumers’ demands. In this context, the assumption that all demands are fully satisfied regardless of the pressure in the system becomes unreasonable. A realistic behavior of the network performance can only be attained by considering demands to be pressure dependent. This paper aims to describe how pressure dependent demand analysis is useful for the simulation of disaster scenario due to source failure of the Shirpur town. The simulation of failure scenario is carried out using WaterGEMs software. The paper also aims to prepare the action plans for the recovery of water supply in such crisis conditions.

Application of modified complementary reservoir approach in analysis of water distribution networks under pressure-deficient conditions

Hydraulic simulation models which simulate water distribution systems in different operating conditions are essential tools to evaluate network reliability. Simulation models found in most commercial software are not effectively capable of analyzing demand nodes under critical conditions such as fire-fighting demand or network pipe breakage. In the current study, a combination of hydraulic model and complementary reservoir solution (CRS) method is used for solving network's problems in critical conditions for both series-looped networks and a part of water network in Ilam city (Iran). Obtained results show that CRS provide more than actual need on the demand node for some reservoir total pressure heads. Thus, two modified versions of CRS method are proposed to deal with failures of CRS in such cases. Obtained results demonstrate improved efficiency in the combined model for analyzing networks in abnormal conditions.

Comparison of solution methods for analyzing water distribution networks under pressure-deficient conditions

Demand-driven analysis method is used in most current existing models for hydraulic evaluation of water supply networks. This method is based on the assumption of constant use, regardless of the available pressure in nodes. Demand-driven analysis method does not have sufficient efficiency in hydraulic analysis of networks under pressure-deficient conditions. In this study, the combination of pressure-deficient network algorithm (PDNA), modified pressure-deficient network algorithm (MPDNA), and complementary reservoir solution (CRS) methods with hydraulic model have been used to analyze series networks, looped networks, and a full-scale distribution network (part of the water network in Ilam city, Iran) in critical operating conditions. The critical condition in networks is created by breakage in a pipe network and fire-fighting demands on one node. Results showed that the required flow in networks has not been quite satisfied. The supplied outflow in the series, looped networks, and zone-6 network which used the three aforementioned methods are calculated as 76.40%, 90.25%, and 98.56% of total network demand, respectively. The results also showed that the number of required iterations to achieve the solutions in the PDNA method is more than in the MPDNA and CRS methods.

Uncertainty quantification of pressure-driven analysis for water distribution network modeling

The hydraulic analysis of water distribution networks (WDNs) is divided into two approaches: namely, a demand-driven analysis (DDA) and a pressure-driven analysis (PDA). In the DDA, the basic assumption is that the nodal demand is fully supplied irrespective of the nodal pressure, which is mainly suitable for normal operating conditions. However, in abnormal conditions, such as pipe failures or unexpected increase in demand, the DDA approach may cause unrealistic results, such as negative pressure. To address the shortcomings of DDA, PDA has been considered in a number of studies. For PDA, however, the head-outflow relation (HOR) should be given, which is known to contain a high degree of uncertainty. Here, the DDA-based simulator, EPANET2 was modified to develop a PDA model simulating pressure deficient conditions and a Monte Carlo simulation (MCS) was performed to consider the quantitative uncertainty in HOR. The developed PDA model was applied to two networks (a well-known benchmark system and a real-life WDN) and the results showed that the proposed model is superior to other reported models when dealing with negative pressure under abnormal conditions. In addition, the MCS-based sensitivity analysis presents the ranges of pressure and available discharge, quantifying service reliability of water networks.