Doosun Kang

Real-Time Demand Estimation and Confidence Limit Analysis for Water Distribution Systems

A real-time estimation of water distribution system state variables such as nodal pressures and chlorine concentrations can lead to savings in time and money and provide better customer service. While a good knowledge of nodal demands is prerequisite for pressure and water quality prediction, little effort has been placed in real-time demand estimation. This study presents a real-time demand estimation method using field measurement provided by supervisory control and data acquisition systems. For real-time demand estimation, a recursive state estimator based on weighted least-squares scheme and Kalman filter are applied. Furthermore, based on estimated demands, real-time nodal pressures and chlorine concentrations are predicted. The uncertainties in demand estimates and predicted state variables are quantified in terms of confidence limits. The approximate methods such as first-order second-moment analysis and Latin hypercube sampling are used for uncertainty quantification and verified by Monte Carlo simulation. Application to a real network with synthetically generated data gives good demand estimations and reliable predictions of nodal pressure and chlorine concentration. Alternative measurement data sets are compared to assess the value of measurement types for demand estimation. With the defined measurement error magnitudes, pipe flow data are significantly more important than pressure head measurements in estimating demands with a high degree of confidence.

Multiperiod Planning of Water Supply Infrastructure Based on Scenario Analysis

AbstractLong-range infrastructure planning is fraught with uncertainties. Population growth may occur faster or slower than expected, regulations may change, and public sentiment can shift. In the face of these uncertainties, water system managers must plan for large infrastructure investments and the questions about when it is desirable to invest in infrastructure and what is the appropriate infrastructure component size to meet growing demands. One of the most powerful and intuitive ways to incorporate uncertainties is to use scenarios that represent plausible futures. Scenario-based planning is gaining acceptance in the water resources community. Preparing for a range of possible futures provides flexibility and adds robustness to the system so it can respond to uncertain events at reasonable costs while maintaining community confidence in their utilities. In this paper, novel scenario-based planning and optimization approaches are presented for the optimal design of regional-scale water supply infrast...

Demand and Roughness Estimation in Water Distribution Systems

To provide more accurate estimates and account for associated uncertainties, a parameter estimation methodology for water distribution systems (WDSs) that combines demand and parameter estimation processes is proposed. A two-step sequential method for dual estimation of demand and roughness coefficient is presented based on a weighted least-squares scheme using field measurements of pipe flow rates and nodal pressure heads under multiple demand conditions. The uncertainties in the estimated variables and resulting nodal pressure predictions are quantified in terms of confidence limits using the first-order second moment method. The algorithm is applied to two network systems including a midsized real WDS. The two-step sequential model provides accurate and precise estimates while joint estimation provides poor estimates.

Resilience/Availability Analysis of Municipal Water Distribution System Incorporating Adaptive Pump Operation

AbstractIn last three decades, the reliability of water distribution systems (WDSs) has become a major concern, not only for water utilities and academic research communities, but also for society as a whole. Notable research has been conducted on the reliability/availability of WDSs, however, little attention has been paid to quantify the impact of adaptive operations as a response to system failure to enhance the resiliency of WDSs. Here, resilience is defined in the general sense as the ability to recover from a failure to a satisfactory state. In practice, if a system fails to supply water with adequate pressure, the water utility would take action to respond. Adaptive actions include switching on additional pumps as a short-term remedy or maintaining a higher water level in storage tanks as a long-term strategy to satisfy system pressure when a system experiences abnormal conditions. Here, a Monte Carlo simulation based framework for the resilience analysis of WDSs is implemented, considering the imp...

Real-time optimal valve operation and booster disinfection for water quality in water distribution systems.

Historically, a water distribution system’s (WDS) hydraulic performance has been the primary operational concern. Over the past two decades, however, more attention has been paid to water quality behavior in WDS and today, water quality level is an equally important issue for many water utilities. In most cases, maintaining disinfectant levels is usually of interest to avoid the bacteria regrowth and to protect against the potential cross-contamination events. However, disinfectants, such as chlorine, decay over time and produce potentially harmful disinfectant by-products when they react with organic material in the water. Therefore, maintaining a minimum chlorine residual requirement throughout the WDS is a complex but important task. When online booster disinfection is combined with source disinfection, it has been shown that the total chlorine dosage can be reduced while maintaining minimum chlorine residuals across the system. Here, optimal valve operation has been combined with booster disinfection ...

Scenario-based robust optimization of regional water and wastewater infrastructure

AbstractUncertainties facing water planners and designers include changes in demand resulting from community growth (temporal and spatial), per capita water use, public perceptions, and regulations. One of the most powerful and intuitive ways to represent these uncertainties in the planning stage is to use scenarios. A scenario represents a realization of the system’s random parameters. Scenario-based analysis provides organizational flexibility by planning for multiple potential future scenarios, each of which may be, although is not necessarily, associated with a probability of occurrence. In this study, a scenario-based multiobjective optimization model for robust optimal design of regional-scale water and wastewater infrastructure is presented. The proposed methodology is demonstrated with an application to the planning of a decentralized water supply and reuse system for a new development area in metropolitan Tucson, where sustainable water supply is a significant issue.

Robustness-Based Design of Water Distribution Systems

AbstractRobustness is generally defined as an ability of a system to maintain its function under a defined set of disturbances. To introduce robustness to the water distribution systems (WDSs) design, chance constrained, or so-called reliability-based models have been formulated. Under variations in system parameters, such as nodal demands and pipe roughness, system reliability is generally measured as the probability that the stochastic nodal pressures will be higher than an allowable minimum pressure limit. However, chance constraints may not be the best formulation to improve system robustness because it focuses on the likelihood of failure under a specified set of conditions rather than developing a solution that consistently provides adequate service. In addition, the reliability-based design requires defining the demand condition, its probability distribution and its statistics, which are not straight forward in practice. To address these difficulties, a robustness index that limits the range of the...

Centralized versus Decentralized Wastewater Reclamation in the Houghton Area of Tucson, Arizona

AbstractReclaimed wastewater is increasingly important to satisfaction of water-sustainability objectives in water-short municipalities throughout the United States and particularly in the Southwest. Water reclamation and reuse present new challenges for urban planners, who now tend to consider renewable freshwater and reclaimed wastewater as unique parts of a single water resources portfolio. Efficiency objectives in geographically dispersed communities lead planners to explore the relative merits of centralized versus decentralized wastewater-treatment capacity when new construction is required. However, the complexity of the planning landscape—in which existing water distribution and sewerage capacities; geographic factors; and uncertainty in growth projections, energy cost, and even the sustainability of existing freshwater supplies contribute to plan selection—suggests that decision support methods can usefully supplement engineering judgment to find a near-optimal level of decentralization in facili...

Optimal meter placement for water distribution system state estimation

Real-time state estimates (SEs) of nodal demands in a water distribution system (WDS) can be developed using data from a supervisory control and data acquisition (SCADA) system. These estimates provide information for improved operations and customer service in terms of energy consumption and water quality. The SE results in a WDS are significantly affected by measurement characteristics, i.e., meter types, numbers, and topological distributions. The number and type of meters are generally selected prior to a SCADA layout. Thus, selecting measurement locations is critical. The aim of this study is to develop a methodology that optimally locates field measurement sites and leads to more reliable SEs. An optimal meter placement (OMP) problem is posed as a multiobjective optimization form. Three distinctive objectives are formulated: (1) minimization of nodal demand estimation uncertainty; (2) minimization of nodal pressure prediction uncertainty; and (3) minimization of absolute error between demand estimat...

Dual Water Distribution Network Design under Triple-Bottom-Line Objectives

Rapid urban growth has stressed limited supplies of high-quality water sources and water shortage has become a major issue in worldwide. Today, sustainable water supply to meet growing demand is a significant concern for water utilities. Developing additional high-quality sources is not necessarily available; it may be costly to convey water from sources that are usually located far from users or there may be legal battles over water rights. A well-proven source that does not have significant conveyance costs and that does not pose water right conflicts is wastewater reclamation for nonpotable uses. A few studies have been completed for the design of reclaimed water distribution through a parallel pipe system. In earlier works, however, attention has mainly focused on the recycling of effluent for large users, such as golf courses, parks, and schools with the objective of minimizing economic cost. As reclaimed water takes on a larger role in many communities’ water supply, the questions of how and what wa...