Groundwater Modeling and Beyond: MODFLOW-and-More-2019 Special Issue.

Abstract

This Foreword introduces the fifth special issue of Groundwater comprised of MODFLOW and More conference presentations hosted at the Integrated GroundWater Modeling Center (IGWMC). The theme for the 2019 edition of the “MODFLOW and More” conference series was “Groundwater Modeling and Beyond.” The papers selected for inclusion in this special issue highlight many aspects of the 2019 conference theme. It is well accepted that the development and application of computational models is a critical element of environmental analysis and decision-making. In many circumstances, particularly where predictions are required under changing stresses, there can be few alternatives. Perhaps as victims of our own success, however, those of us who use models as one among many tools to evaluate systems (referred to, incompletely, as “modelers”) are tasked with representing increasingly complex systems. Consequently, many quantitative hydro(geo)logists feel driven to construct equally complex models. Complexity can take many forms, including the mathematical rigor of the equations of state, the level of detail in the conceptual system model, spatial and temporal discretization, and parameterization. Time-and-again, however, in previous “MODFLOW and More” conferences, other venues and publications, it has been demonstrated that increasing simulation complexity offers no guarantee of improved reliability. How, then, to inspire confidence and provide value? In light of the growing challenges imposed by an ever-changing climate, population growth, and the global struggle for improved and equitable living standards, the Organizing Committee of the 2019 conference challenged attendees to explore whether our increasingly sophisticated models are sufficiently reliable to help solve the problems we face, and how we can further adapt and improve our methods and codes to meet these challenges. One area of emphasis was the use of groundwater models to evaluate the transport of chemicals, nutrients, and energy. Aspects of this issue were tackled in the presentations of Chris Langevin (“Hydraulic-Head Formulation for Density-Dependent Flow and Transport”), David Krcmar (“Assessing the Impact of a Heated Basement on Groundwater Temperatures in Bratislava, Slovakia”), and Al Valocchi (“Flux-Corrected Transport with MT3DMS for Positive Solution of Transport”). A second area of focus was the challenge of developing models to evaluate and predict the sustainable yield of integrated groundwater and surface water systems. Aspects of this issue were tackled in the presentations of Lauren Thatch (“Integrated Hydrologic Modeling to Untangle the Impacts of Water Management During Drought”) and Hoang Tran et al. (“Simulating Groundwater-Streamflow Connections in the Upper Colorado River Basin”). Though water resource availability is often evaluated on a local to regional scale, there is increasing interest in understanding and simulating water resources on national, continental, and even global scales. The development and application of water resource models on these scales pose additional challenges. Robert Reinecke tackles one particularly vexing issue—that of determining the appropriate discretization for “giant”-scale models—and provides some recommendations in his presentation (“Importance of Spatial Resolution in Global Groundwater Modeling”). Where suitable data are available, the process of calibrating our models can provide valuable feedback regarding their reliability. Though valuable, the calibration of increasingly large and sophisticated models is not for the faint-of-heart. Challenges posed by calibration of such models are touched upon to some degree in each of the foregoing articles, and are a focus of the presentation by John Doherty (“Decision-Support Modeling: Data Assimilation and Strategic Abstraction”), which combines elements of his 2019 Darcy Lecturer series to challenge modelers to combine the use of the sophisticated modeling tools together with data assimilation and abstraction techniques to identify the appropriate level of model complexity to support decision-making. The recognition of the foregoing challenges is further demonstrated by the selection of one of the co-conveners (Reed Maxwell) as the 2020 Darcy Lecturer, who provides three lectures related to important aspects of these topics. One thing is for certain: there are many motivated and talented scientists working worldwide to meet these challenges. We hope that the themes encompassed by the selection of articles provided in this special issue of Groundwater inspire your modeling research and practice, and that you find the opportunity to share your experiences, expertise, and lessons-learned at the next “MODFLOW and More” conference, to be held at Colorado School of Mines in Golden, Colorado in the early summer of 2021.