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This study is an effort to investigate two parameter estimation approaches in groundwater modeling, sequential and combined. Most researches imply that simultaneous use of flow and transport observations would be more beneficial in parameter estimation, however some other researchers rise questions about this approach. They believe due to the differing geological properties of aquifers and consequently differing mathematical basis of groundwater flow compared to transport simultaneous use of different observations might not be useful in every cases. Despite the fact that parameter estimation or inverse modeling is not a new method in groundwater modeling, most modelers tend to use forward modeling to estimate parameters. In this research a synthetic heterogeneous K-field is created using SGeMS Sequential Gaussian Simulation. This K-field, derived zones of porosity and defined boundary conditions make our simulated confined aquifer. The model synthetic observations obtained from forward models MODFLOW and MODPATH, are used in the process of parameter estimation using PEST++. In order to have a better look at the model and find its weak points, different scenarios have been defined. Applying the principle of parsimony, difficulties have been added gradually in each scenario for the model. The sequential approach performs two calibrations: a flow calibration using head observations followed by the transport calibration using travel time observations. Both sets of observations are applied simultaneously in a single calibration run in the combined approach. Although, comparing estimated parameters with the initial synthetic reality values shows the better modeled results for both hydraulic conductivity and porosity while we apply combined approach. However time-cost along with difficulties to find a best weighs in combined approach imply that these differences are not significant.
This book is Volume 2 which is published to complement "Environmental Processes and Management: Tools and Practices" (https://link.springer.com/book/10.1007/978-3-030-38152-3), 2020 This book provides an in-depth, well-researched and science-based approach to applying key project management and spatial tools and practices in environmental projects. This book is an important read for leaders considering projects that balance social–economic growth against minimizing its ill effects on Planet Earth. This book brings together several aspects of groundwater engineering, as well as the formula and analytical approaches required for more informed decision-making. It also highlights the vital importance of understanding the technological, economic and social dimensions of environmental studies explained through dynamic approaches and illustrative figures that have short-term results and long-term impacts. This book emphasizes on encouraging the modern and vibrant research works conducted by young researchers across the world. This book clearly details the general application of fundamental groundwater processes, the character of the different types of systems in which they occur and the way in which these factors influence process dynamics, environmental systems and their possible remedies. The book sets a possible recommendation for the professionalism with which environmental research should be planned, executed, monitored, assessed and delivered. While primarily intended for professionals responsible for the management of groundwater projects or interested in improving the overall efficiency of such projects, it is also useful for managers in the private, public and not-for-profit sectors. The book is a valuable resource for students at both undergraduate and postgraduate levels. In addition, this book serves as an indispensable guide for anyone willing to develop their skills in modern groundwater / environmental management and related techniques
Numerical models of flow and transport processes are heavily employed in the fields of surface, soil, and groundwater hydrology. They are used to interpret field observations, analyze complex and coupled processes, or to support decision making related to large societal issues such as the water-energy nexus or sustainable water management and food production. Parameter estimation and uncertainty quantification are two key features of modern science-based predictions. When applied to water resources, these tasks must cope with many degrees of freedom and large datasets. Both are challenging and require novel theoretical and computational approaches to handle complex models with large number of unknown parameters.
Methods and guidelines for developing and using mathematical models Turn to Effective Groundwater Model Calibration for a set of methods and guidelines that can help produce more accurate and transparent mathematical models. The models can represent groundwater flow and transport and other natural and engineered systems. Use this book and its extensive exercises to learn methods to fully exploit the data on hand, maximize the model's potential, and troubleshoot any problems that arise. Use the methods to perform: Sensitivity analysis to evaluate the information content of data Data assessment to identify (a) existing measurements that dominate model development and predictions and (b) potential measurements likely to improve the reliability of predictions Calibration to develop models that are consistent with the data in an optimal manner Uncertainty evaluation to quantify and communicate errors in simulated results that are often used to make important societal decisions Most of the methods are based on linear and nonlinear regression theory. Fourteen guidelines show the reader how to use the methods advantageously in practical situations. Exercises focus on a groundwater flow system and management problem, enabling readers to apply all the methods presented in the text. The exercises can be completed using the material provided in the book, or as hands-on computer exercises using instructions and files available on the text's accompanying Web site. Throughout the book, the authors stress the need for valid statistical concepts and easily understood presentation methods required to achieve well-tested, transparent models. Most of the examples and all of the exercises focus on simulating groundwater systems; other examples come from surface-water hydrology and geophysics. The methods and guidelines in the text are broadly applicable and can be used by students, researchers, and engineers to simulate many kinds systems.
Several of the papers here deal with decision making under uncertainty.
This new edition adds several new chapters and is thoroughly updated to include data on new topics such as hydraulic fracturing, CO2 sequestration, sustainable groundwater management, and more. Providing a complete treatment of the theory and practice of groundwater engineering, this new handbook also presents a current and detailed review of how to model the flow of water and the transport of contaminants both in the unsaturated and saturated zones, covers the protection of groundwater, and the remediation of contaminated groundwater.
This second edition is extensively revised throughout with expanded discussion of modeling fundamentals and coverage of advances in model calibration and uncertainty analysis that are revolutionizing the science of groundwater modeling. The text is intended for undergraduate and graduate level courses in applied groundwater modeling and as a comprehensive reference for environmental consultants and scientists/engineers in industry and governmental agencies. Explains how to formulate a conceptual model of a groundwater system and translate it into a numerical model Demonstrates how modeling concepts, including boundary conditions, are implemented in two groundwater flow codes-- MODFLOW (for finite differences) and FEFLOW (for finite elements) Discusses particle tracking methods and codes for flowpath analysis and advective transport of contaminants Summarizes parameter estimation and uncertainty analysis approaches using the code PEST to illustrate how concepts are implemented Discusses modeling ethics and preparation of the modeling report Includes Boxes that amplify and supplement topics covered in the text Each chapter presents lists of common modeling errors and problem sets that illustrate concepts
This research compares two approaches to the application of formal calibration methods to groundwater modeling: sequential and combined. There exists research, both theoretical work and field studies, that point to improved estimation of hydraulic parameters when multiple types of observations, flow and transport, are applied simultaneously. There also exist theories about why combined calibration might not be compatible with the differing mathematical basis of flow compared to transport. This research has taken a closer look at the mechanisms at work by comparing these approaches when the input parameters are known. Using stochastic methods instead of field data, the original input parameters are specified. A synthetic heterogeneous K field is simulated using SGeMS Sequential Gaussian Simulation. This K-field, derived zones of porosity and defined boundary conditions comprise the simulation of a large confined aquifer. Two sets of synthetic observations obtained from forward models MODFLOW and MODPATH, heads and travel times, guide the calibration. Applying PEST++, the sequential approach performs two calibrations: a flow calibration using heads followed by a transport calibration using travel times. Both sets of observations are applied simultaneously in a single calibration run in the combined approach. Comparing final parameter estimates of each approach to the initial synthetic reality values shows that better results were achieved for both hydraulic conductivity and porosity with the combined approach. However, the sequential approach performed well with results falling within one standard deviation of the true values.
Written by renowned experts in the field, this book assesses the status of groundwater models and defines models and modeling needs in the 21st century. It reviews the state of the art in model development and application in regional groundwater management, unsaturated flow/multiphase flow and transport, island modeling, biological and virus transport, and fracture flow. Both deterministic and stochastic aspects of unsaturated flow and transport are covered. The book also introduces a unique assessment of models as analysis and management tools for groundwater resources. Topics covered include model vs. data uncertainty, accuracy of the dispersion/convection equation, protocols for model testing and validation, post-audit studies, and applying models to karst aquifers.
... A diskette with the updated programme of Appendix C and examples is available through the author at a small fee. email: [email protected] fax: 1--310--825--5435 ... This book systematically discusses basic concepts, theory, solution methods and applications of inverse problems in groundwater modeling. It is the first book devoted to this subject. The inverse problem is defined and solved in both deterministic and statistic frameworks. Various direct and indirect methods are discussed and compared. As a useful tool, the adjoint state method and its applications are given in detail. For a stochastic field, the maximum likelihood estimation and co-kriging techniques are used to estimate unknown parameters. The ill-posed problem of inverse solution is highlighted through the whole book. The importance of data collection strategy is specially emphasized. Besides the classical design criteria, the relationships between decision making, prediction, parameter identification and experimental design are considered from the point of view of extended identifiabilities. The problem of model structure identification is also considered. This book can be used as a textbook for graduate students majoring in hydrogeology or related subjects. It is also a reference book for hydrogeologists, petroleum engineers, environmental engineers, mining engineers and applied mathematicians.