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Dr. Longcang SHU Prof. of Hydrogeology College of Hydrology & Water Resources. Numerical Simulation of Groundwater. Contents. Chapter 1 Introduction Chapter 2 Equations & Numerical Methods Chapter 3 The Conceptual Model Chapter 4 Boundaries Chapter 5 Sources and Sinks
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Dr. Longcang SHU Prof. of Hydrogeology College of Hydrology & Water Resources Numerical Simulation of Groundwater
Contents Chapter 1 Introduction Chapter 2 Equations & Numerical Methods Chapter 3 The Conceptual Model Chapter 4 Boundaries Chapter 5 Sources and Sinks Chapter 6 Calibration and Application Process Chapter 7 Case Study
References 1. Anderson, M.P., and W.W. Woessner, Applied Groundwater Modeling-simulation of flow and advective transport, Academic Press, Inc. 1992. 2. Maidment D.R., et al, Handbook of Hydrology, McGraw-Hill, INC. 1993. 3. Ground Water 4. Water Resources Research 5. Journal of American Water Resources Association
1. What changes can be expected in groundwater levels in the aquifers beneath Beijing, in the year 2020? 2. How will a change in stream stage affect the water table in an adjacent alluvial aquifer in Jining, Shandong Province?
Hydrogeologists are often called upon to predict the behavior of groundwater systems by answering questions like these.
Providing answers to these seemingly simple questions involves formulating a correct conceptual model, selecting parameter values to describe spatial variability within the groundwater flow system, as well as spatial and temporal trends in hydrologic stresses and past and future trends in water levels.
The best tool available to help hydrogeologists meet the challenge of prediction is usually a groundwater model.
1.1 What is a Model? A model is any device that represents an approximation of a field situation. Physical Model Mathematical Model
Physical models such as laboratory sand tanks simulate groundwater flow directly.
A mathematical model simulates groundwater flow indirectly by means of a governing equation thought to represent the physical processes that occur in the system, together with equations that describe heads or flows along the boundaries of the model (boundary conditions).
For time-dependent problems, an equation describing the initial distribution of heads in the system also is needed (initial conditions). Mathematical models can be solved analytically or numerically.
Mathematical Model A mathematical model simulates groundwater flow indirectly by means of a governing equation thought to represent the physical processes that occur in the system, together with equations that describe heads or flows along the boundaries of the model (boundary conditions).
1. Models are worthless because they require too many data and therefore are too expensive to assemble and run. Furthermore, they can never be proved to be correct and suffer from a lack of scientific certainty.
2. Models are essential in performing complex analyses and in making informed predictions.
1.2 Why Model? Most groundwater modeling efforts are aimed at predicting the consequences of a proposed action. It requires calibration.
Models can also be used in an interpretive sense to gain insight into the controlling parameters in a site-specific setting or as a framework for assembling and organizing field data and formulating ideas about system dynamics. It does not necessarily require calibration.
Functions of model: A hydrogeologic simulation model is developed to reach a management decision. Simulation models serve at least three roles in this regard:
1. To provide insight to the hydrologic processes operative in the study area;
2. To develop predictions of system behavior under changed conditions;
3. To test alternative hypotheses on system behavior to guide site investigation plans and to increase the confidence level in the management decision.
1.3 Modeling Steps 1. Conceptual model: 2. Mathematical model: 3. Calibration: Calibration is done by trial-and-error adjustment of parameters or by using an automated parameter estimation code. 4. Verification: The purpose of model verification is to establish greater confidence in the model by using the set of calibrated parameter values and stresses to reproduce a second set of field data. 5. Prediction:
Successful modelers understand the science behind the models they use and have considerable experience in applying models to practical problems. In the process, one learns how to describe the problem domain, select boundary conditions, assign model parameters, and calibrate the model.
Groundwater models can be divided broadly into two categories: 1. Groundwater flow model: to solve for the distribution of head; 2. Groundwater solute transport model: to solve for concentration of solute, usually contaminants, as affected by advection, dispersion, and chemical reactions.
