Use Of Groundwater Models Research Articles

A fully-explicit discontinuous Galerkin hydrodynamic model for variably-saturated porous media

Groundwater flows play a key role in the recharge of aquifers, the transport of solutes through subsurface systems or the control of surface runoff. Predicting these processes requires the use of groundwater models with their applicability directly linked to their accuracy and computational efficiency. In this paper, we present a new method to model water dynamics in variably-saturated porous media. Our model is based on a fully-explicit discontinuous-Galerkin formulation of the 3D Richards equation, which shows a perfect scaling on parallel architectures. We make use of an adapted jump penalty term for the discontinuous-Galerkin scheme and of a slope limiter algorithm to produce oscillation-free exactly conservative solutions. We show that such an approach is particularly well suited to infiltration fronts. The model results are in good agreement with the reference model Hydrus-1D and seem promising for large scale applications involving a coarse representation of saturated soil.

The Value of Groundwater Modeling to Support a Pump and Treat Design

AbstractA wide range of rules, algorithms, and models are available to design an effective pump and treat remediation system. Often, one refers to the effectiveness of the developed pump and treat system to demonstrate how valuable the use of a groundwater model can be. An economic valuation of the groundwater model is usually missing. This study provides a framework that puts the discussion concerning the use of groundwater models in an economic perspective. It is not only demonstrated that a more effective pump and treat system can be designed using a groundwater model, but also the economic implications of using a groundwater model are calculated. A set of economic decision rules is applied to determine the economic value of a groundwater model. It is shown that investing in a groundwater model can be economically worthwhile. The remediation time is reduced, remediation costs are saved and the property can be sold more early. These benefits outweigh the costs of developing a groundwater model, and hence a positive net benefit (NB) is determined.

Groundwater flow model management and case studies in Emilia-Romagna (Italy)

The use of groundwater modeling to support the planning and management of water resources is a possible goal of a long and detailed course of study and research. The present work concerns some applications carried out within the aquifers of the Emilia-Romagna plain in northern Italy. The main features of the developed and available mathematical models are reported as well as the geological and hydrogeological description of the analyzed aquifers. The main operational choices that have characterized the implementation of all models and their continuous development and updating are discussed. Activity has been focused to maintain active the data stream between the models to improve their functionality along with time to give a basis for models management. Models have been used in different applications which indicate the potential for their use with targeted objectives of planning and management. Two examples at two different scales are given: the first shows the application to the entire aquifer of the Emilia-Romagna region, which has been able to adapt simulations to new groundwater bodies defined in accordance with 2000/60/EC directive, the current regulatory framework for the planning of water resources. This framework provides for the establishment of programs of measures whose level of effectiveness can be estimated with the support of models. The second concerns a more detailed scale model in reference to a specific evaluation of feasibility of an intervention of artificial recharge. The management approach used here is the result of over 10 years development and application and now allows to apply numerical models in a role of systematic service in support of the institutions involved in planning and management of groundwater resources.

About this title ‐ Groundwater Resources Modelling: A Case Study from the UK

The UK is a country with over 150 years of widespread exploitation of its principal aquifers for public water supply. Increasing demands, greater awareness of environmental pressures and more exacting legislation has heightened the need for quantitative models to predict the impacts of groundwater use. In the UK this has culminated in a unique national, regulator-led programme for England and Wales to develop conceptual and numerical models of the principal bedrock aquifers. The outcomes of this programme will be of interest to the international hydrogeological community, particularly as international legislation such as the European Water Framework Directive requires management of water issues across administrative boundaries with a varied cast of stakeholders. The collection of papers provides a contrast between practitioner- and research-based approaches to assess and predict the anthropogenic impacts and environmental pressures. Many insights are provided on how the regular use of groundwater models may address the environmental challenges of the future.

The National Groundwater Modelling System: providing wider access to groundwater models

Abstract The National Groundwater Modelling System (NGMS) is a map-based, client–server system for holding groundwater models and supporting documentation. Models can be run, new ‘what-if’ scenarios created, and time series and spatial data rapidly viewed and exported. Use of the system will result in greater standardization of data formats, model codes and methods used by the Environment Agency without stifling technological progress. NGMS enables a wider audience of water resource staff to access groundwater models. The system is being used to improve representation of groundwater in Catchment Abstraction Management Strategies and to forecast the potential impacts of climate change upon water resources. However, the day-to-day, operational use of groundwater models by the Environment Agency remains a challenge that requires engagement with other specialists (e.g. hydrologists and IT systems specialists). Considerable effort is required to roll out the system, train people and adapt operational decision-making processes to bring NGMS into regular and safe use.

Editor’s message: Groundwater modeling fantasies—part 2, down to earth

Creating a model structure and determining values of model parameters is not a science, but rather an intuitive exercise, hopefully carried out with some wisdom concerning how natural systems function. Whether warranted or not, whether useful or not, parameter estimation has become a major part of model creation and this evolution has been fueled by the recent wide availability of automatic estimation software. In some sense, this wide availability has promulgated greater fallacious use of groundwater models. Automatic estimation software is truly a wonderful convenience when used properly, but it is no more than a convenience—and it should not be the primary objective of a modeling analysis to use it. The most-common estimation technique relies on the rather arbitrary assumption that a minimized least-squares objective function fit is the best one. There are other equally valid objective functions and estimation approaches, rarely used today, and these would give different parameter estimates in the same model. Error structure is another assumption rarely tested when fitting models to data. Should we be minimizing the error that is the square of absolute differences between model predictions and observations or perhaps the square of the differences in logarithm of model predictions and observations, or perhaps differences of another function of model predictions and observations? These all assume different error distributions. The choice between the first two possibilities is most often expressed in automatic estimation software via weighting of observation values. The selection is usually made by a modeler who is oblivious to the issues involved. This selection makes a huge difference in the estimated values of model parameters, but is not often admitted to be a major ambiguity in results. The selection yields additional uncertainty in model predictions. Deciding on the simplicity or complexity of a model when doing automatic calibration, here meaning determining the number of parameters that will be estimated, by turning a knob on a mathematical objective function, is one of many totally arbitrary possible approaches to simplification—and is not necessarily better or worse than other mathematical or scientific-judgment/human-intuition-based approaches. An objective function is merely one artificial construct to express what is desired from the model fit. There is no correct objective and no correct approach to regularization, and various such objectives will give different model complexities and different parameter estimates. Whether some are better than others is a matter of discussion, never to be fully resolved. In the experience of this writer, if there are more than perhaps ten parameters in a groundwater model of an actual area, some of the parameters become highly correlated and their individual values cannot be distinctly determined by automatic estimation. We might have a good discussion about how many parameters are appropriate to estimate for your current model.

Combined use of groundwater modeling and potential zone analysis for management of groundwater

A methodology for groundwater evaluation has been developed by the combined use of numerical model and spatial modeling using GIS. The developed methodology has been applied on the sub-basin of the Banganga River, India. Initially, the groundwater potential zones have been delineated by spatial modeling. Different thematic maps of the basin like geology, geomorphology, soil, drainage, slope factor and landuse/landcover have been used to identify the groundwater potential zones. Further, the groundwater flow model for the study area has been developed in the MODFLOW. The groundwater flow vector map has been developed and superimposed on the potential zone map to validate the results of spatial modeling. Finally, the different scenarios have been conceptualized by varying the discharge of the wells and purposing the location for new rainwater harvesting structures. Results reveal that increasing the discharge of the wells in the potential zones put less stress on the aquifer. The suggested locations of rainwater harvesting structures also help to reduce the overall decline of groundwater in the area. The hydrological and spatial modeling presented in this study is highly useful for the evaluation of groundwater resources and for deciding the location of rainwater harvesting structures in semi-arid regions.

Groundwater Modeling in Integrated Water Resources Management—Visions for 2020

Groundwater modeling is undergoing a change from traditional stand-alone studies toward being an integrated part of holistic water resources management procedures. This is illustrated by the development in Denmark, where comprehensive national databases for geologic borehole data, groundwater-related geophysical data, geologic models, as well as a national groundwater-surface water model have been established and integrated to support water management. This has enhanced the benefits of using groundwater models. Based on insight gained from this Danish experience, a scientifically realistic scenario for the use of groundwater modeling in 2020 has been developed, in which groundwater models will be a part of sophisticated databases and modeling systems. The databases and numerical models will be seamlessly integrated, and the tasks of monitoring and modeling will be merged. Numerical models for atmospheric, surface water, and groundwater processes will be coupled in one integrated modeling system that can operate at a wide range of spatial scales. Furthermore, the management systems will be constructed with a focus on building credibility of model and data use among all stakeholders and on facilitating a learning process whereby data and models, as well as stakeholders' understanding of the system, are updated to currently available information. The key scientific challenges for achieving this are (1) developing new methodologies for integration of statistical and qualitative uncertainty; (2) mapping geological heterogeneity and developing scaling methodologies; (3) developing coupled model codes; and (4) developing integrated information systems, including quality assurance and uncertainty information that facilitate active stakeholder involvement and learning.

The Role of Uncertainty in the Use of Ground Water Models for Administration of Water Rights

Competing demands for water resources are creating high profile disputes throughout the western United States. Models are increasingly being used to help sort out the disputes. Invariably, the models themselves end up being the object of court cases due to the inherent uncertainty of modeling natural systems (Cosens 2006). As the water use issues were brought to a head by persistent drought in the eastern Snake River Plain in southeastern Idaho, the Idaho Department of Water Resources (IDWR) embarked on developing a ground water model which would become the basis for conjunctively managing the surface and ground water resources. Recognizing that model uncertainty has been used in the past to undermine the use of scientific models in natural resource management, IDWR attempted to address model uncertainty through a consensus approach. With a priori knowledge of the major points of dispute, IDWR invited the primary water users to have their hydrologic consultants participate in the re-formulation of the ground water model of the eastern Snake River Plain aquifer. In some respects, this constituted using a social approach to address the issue of model uncertainty. A similar approach was successfully used in developing a surface water model in the Milk River Basin in Montana (Cosens 2006). The purpose of this paper is to draw on experiences gained in the eastern Snake River Plain in Idaho to propose some concepts of the use of models in supporting conjunctive administration decisions and the role of uncertainty in that process.

Road de-icing salt as a potential constraint on urban growth in the Greater Toronto Area, Canada

North America's fifth most populated municipality — the Greater Toronto Area (GTA) — is undergoing rapid urban development with serious questions being raised regarding the long-term impacts of urban growth on the quality and quantity of ground and surface water. Degradation of groundwater quality by NaCl de-icing salt is the primary concern since there are no cost effective alternatives to NaCl de-icing salt and there is little evidence that salt loadings to the subsurface can be significantly reduced. In 2001, the issue acquired a new sense of urgency when de-icing chemicals containing inorganic chloride salts (with or without ferrocyanide de-caking agents) were designated as toxic under the Canadian Environmental Protection Act. To heighten concerns, future growth in the GTA will inevitably take place in areas where groundwater is regularly used for potable supply. Studies using groundwater flow and transport models show that significant deterioration of groundwater quality can be expected in shallow aquifers as a result of urban development with chloride concentrations approaching the drinking water quality standard of 250 mg/l. Results demonstrate that urban planning needs a fresh approach that explicitly includes groundwater protection and aquifer management in the decision-making process, clearly defines acceptable environmental performance standards and makes greater use of groundwater models to evaluate alternative urban designs.

Estimating Ground Water Yield in Small Research Basins

AbstractAn analysis of ground water recharge in 32 small research watersheds shows the average flow of ground water out of the watershed (deep seepage) is 45% of streamflow and ranges from 8 to 350 mm/year when apportioned over the watershed area. It is time to meld ground water and small watershed science. The use of well networks and the evaluation of ground water well hydrographs or the use of ground water models to estimate deep seepage from small research basins is highly recommended. Future investigators are now armed with better tools necessary to estimate all the water and nutrients and have no need to quietly assume deep seepage is zero.

Assessing impacts of basin management and environmental change in the Eastern Murray Basin

The Lower Murrumbidgee groundwater model was developed to improve the understanding of the regional flow system, and to evaluate the impact of large scale land management options and climate change on the water and salt balance for the major regional aquifers within the Eastern Murray Basin (Punthakey et al., 1994). The model covers approximately 39,000 km 2 equivalent to 13% of the Murray Geological Basin, and comprises three layers. Each layer represents a major regional aquifer system, the Shepparton, Calivil and Renmark. The model was calibrated using observed potentiometric data from 1980 to 1985. Comparison of contours of observed heads and modelled heads for the Shepparton, Calivil and Renmark showed that the modelled heads matched the observed head contours closely. The Lower Murrumbidgee groundwater model has shown that large areas of the current irrigation areas and districts will be affected by rising groundwater by 2020 under the ‘Do nothing’ scenario. The ‘Deep groundwater pumping’ scenario appeared to offer the best long-term option for controlling high water tables while at the same time offering the possibility for trading existing surface water entitlements. The use of groundwater models to investigate the impacts of environmental change within the Basin such as planting trees along riverine corridors and their impact on shallow water tables in the Shepparton aquifer was investigated. The ‘Shallow groundwater pumping’ scenario appeared to control the rate of rise in water table in the Shepparton, although the disposal of large quantities of saline groundwater pumped from the Shepparton presents a major disposal problem. An increase in irrigation recharge in the Irrigation Areas and Districts, and on Private Irrigation Properties would result in unacceptably high water tables in the CIA, Wah Wah, and in the northeastern part of the model domain. Any proposal for increased irrigation would therefore have to be evaluated closely for impacts. The model can be used to provide a window into the future of likely impacts to the area under a range of scenarios. The implementation of a specific option will however depend on its economic merit to the community and the area.

Along the waterfront

James W. Mercer, of GeoTrans, Inc. (Herndon, Va.), will present the 26th Henry W. Shaw Lecture in Civil Engineering on April 15, 1988, at North Carolina State University, Raleigh. The title of his talk will be “Use of Groundwater Models: The Settlement Process at the Chem‐Dyne Hazardous Waste Site.”The National Water Well Association's Special Recognition Award was presented to AGU member Fletcher G. Driscoll of White Bear Lake, Minn.