Applied Groundwater Modeling
Applied Groundwater Modeling
Art and science have their meeting point in method.
Edward George Bulwer-Lytton
This second edition is motivated by the many significant developments in groundwater modeling since the first edition was published in 1992. The increased computational speed and capacity of present day multicore computers as well as the availability of sophisticated graphical user interfaces (GUIs) and geographical information systems have transformed groundwater modeling. But more importantly, new ways of calibrating models and analyzing uncertainty and new powerful codes that provide enhanced modeling tools are revolutionizing the science of groundwater modeling. In this second edition, we discuss many of the important advances in applied groundwater modeling introduced since 1992 and also update the treatment of fundamentals of groundwater flow modeling covered in the first edition. The chapters on model calibration and forecasting ( Chapters 9 and 10 in the second edition) are entirely new and include discussion of new tools for parameter estimation and uncertainty analysis in forecast simulations. Similar to the first edition, our book is intended as an introduction to the applied science of modeling groundwater flow. We focus on groundwater modeling practice. For a more theoretical approach to groundwater modeling, the reader is referred to textbooks by Diersch (2014) and Bear and Cheng (2010) . Quantitative analysis of groundwater flow is essential to all hydrogeological problems, and groundwater models are the essential tools in such analyses. Groundwater flow models solve for what cannot be fully observed or measured-the distribution of head in space and time. Important associated information such as water budgets, flow rates, and flowpaths to and from surface water bodies and wells can be calculated from the head distribution. The focus of our book is mastering groundwater flow models, a critical first step for a groundwater modeler. Although many groundwater problems can be solved by analyzing groundwater flow alone, some problems require analysis of the movement of solutes or contaminants in the subsurface. A transport model includes representation of advective transport, dispersion, and chemical reactions to solve for solute or contaminant concentrations. Transport modeling is beyond the scope of our textbook but is covered in detail by Zheng and Bennett (2002) . However, the starting point for transport modeling is a good groundwater flow model because a transport code uses output from a groundwater flow model. Moreover, some transport problems can be addressed by considering only advective transport using a particle tracking code as a postprocessor to a groundwater flow model to calculate flowpaths and travel times. We discuss those types of problems in a chapter on particle tracking ( Chapter 8 in the second edition) that was revised and updated from the first edition. Mastery of groundwater modeling requires both art and science. The science of groundwater modeling includes basic modeling theory and numerical solution methods. There are many textbooks that provide advanced, intermediate, and elementary treatments of the science and underlying mathematics of numerical modeling of groundwater flow. Since 1992, applied groundwater science has expanded to include theory and methods for parameter estimation (inverse solutions) and uncertainty analysis, and there are books devoted exclusively to those topics (e.g., Doherty, 2015 ; Aster et al., 2013 ; Hill and Tiedeman, 2007 ). Although our text provides some of the background information for applying groundwater models to field problems, we assume that the reader knows the basic principles of hydrogeology and modeling as covered in standard textbooks such as Fitts (2013) , Kresic (2007) , Todd and Mays (2005) , Sch