USGS

System and Boundary Conceptualization
in Ground-Water Flow Simulation

Techniques of Water-Resources Investigations of the United States Geological Survey, Book 3, Applications of Hydraulics, Chapter B8

 

By Thomas E. Reilly

 

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CONTENTS

Abstract

Introduction

Selection and simulation of physical features of ground-water systems as boundary
conditions in ground-water flow models

Streams

Lakes and reservoirs

Wetlands

Springs

Recharge at the water table

Earth materials of low hydraulic conductivity

Inter-basin flow

Ground-water evapotranspiration

Spatial changes in density of water

Ground-water divides

Artificial boundaries that are not physical features

Examples of the conceptualization of boundary conditions for two ground-water models

Conceptualization of the Albuquerque Basin, New Mexico ground-water flow system

Boundary conditions associated with physical features at the lateral extent of the model

Boundary conditions associated with physical features at the bottom of the model

Boundary conditions associated with physical features at the top of the model

Water budget for the system

Conceptualization of the Long Island, New York ground-water flow system

Boundary conditions associated with physical features at the lateral extent of the model

Boundary conditions associated with physical features at the bottom of the model

Boundary conditions associated with physical features at the top of the model

Water budget for the system

Summary and Conclusions

Acknowledgments

Selected References

Appendix 1. List of “Packages” in the U.S. Geological Survey Modular Three-Dimensional
Ground-Water Flow Model (MODFLOW) used to represent physical features of a
ground-water system as mathematical boundary conditions

Techniques of Water-Resources Investigations of the U.S. Geological Survey

Abstract

Ground-water models attempt to represent an actual ground-water system with a mathematical counterpart. The conceptualization of how and where water originates in the ground-water-flow system and how and where it leaves the system is critical to the development of an accurate model. The mathematical representation of these boundaries in the model is important because many hydrologic boundary conditions can be mathematically represented in more than one way. The determination of which mathematical representation of a boundary condition is best usually is dependent upon the objectives of the study. This report focuses on the specific aspect of describing different ways to simulate, in a numerical model, the physical features that act as hydrologic boundaries in an actual ground-water system. The ramifications, benefits, and limitations of each approach are enumerated, and descriptions of the representation of boundaries in models for Long Island, New York, and the Middle Rio Grande Basin, New Mexico, illustrate the application of some of the methods.


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