The Groundwater Project

Getting Started with MODFLOW

Publication year: 2023
Number of pages: 242

ISBN: 978-1-77470-030-3

Author:

Richard B. Winston: Maryland, USA

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Last Update: 30 January 2024
Released: 6 November 2023​

Description

Numerical modeling of groundwater flow systems was once accessible only to modeling specialists in the hydrogeological community. Software such as MODFLOW—the most frequently used groundwater modeling program in the world—and associated graphical user interfaces (GUIs) have made modeling possible for most groundwater scientists. This book provides the bridge from understanding to implementing models by introducing the basics of MODFLOW version 6 and providing readers who have a working knowledge of groundwater flow with a guide through construction of their first groundwater model.

The author helps the reader understand the conceptual basis of MODFLOW while avoiding detailed mathematics. The book begins with how to install the program and use it to simulate groundwater flow. Exercises lead the reader step-by-step through model set up so that they can apply it to their own field data. The exercises use the free graphical user interface ModelMuse but are explained in a way that allows the reader to use another GUI if they prefer. The hands-on learning culminates in a final exercise that demonstrates how a MODFLOW model is constructed for a field site.

This “getting started” guidebook is intended to help the user go beyond the basics. MODFLOW is a powerful tool for gaining insight into hydrogeological controls on flow in a groundwater system. Accordingly, users can apply MODFLOW to further refine their thinking at all stages of their project—including the early stages in which they develop and improve the underlying conceptual model.

Thus, this book Getting Started with MODFLOW enables hydrogeologists who do not specialize in modeling to participate in flow simulation to predict and investigate groundwater flow and head in response to human activities and natural phenomena. The book provides wider accessibility to this powerful tool for those working in education, research, management, protection, and remediation of groundwater flow systems.

Interview with Author

Contents

1 INTRODUCTION

1.1 Assumptions in Modflow

1.2 First Steps

2 INSTALLING MODFLOW

2.1 Installing Modflow and Modpath

2.2 Installing Modelmuse

2.3 Installing Listinganalyst

3 ORIENTATION TO MODELMUSE

3.1 Defining the Initial Grid

3.2 The Main Modelmuse Window

3.3 Activating Modflow Packages

3.4 Data Sets

3.5 Data Visualization

3.6 Run Modflow

3.7 Objects

3.8 Import Model Results

4 CREATING A SIMPLE MODFLOW MODEL

4.1 Run an Example Modflow Model

4.2 Model Requirements

4.3 Starting a New Modflow Model

4.4 Define Stress Periods

4.5 Specify Hydraulic Conductivity

4.6 Defining Specified Head Boundaries

4.7 Running the Model

4.8 View Model Results

4.9 Modflow Input and Output Files

5 DISCRETIZATION IN TIME AND SPACE

5.1 Consistent Units

5.2 The Grid

5.2.1 Stuctured Grids
5.2.2 Discretization by Vertices
5.2.3 Unstructured Grids
5.2.4 Grid Design
5.2.5 Active Cells

5.3 Stress Periods

5.3.1 Time Step Multipliers
5.3.2 Steady State Versus Transient

6 INITIAL CONDITIONS

7 REPRESENTATION OF PROPERTIES OF GEOLOGIC MATERIALS

7.1 The Node Property Flow Package

7.2 The Storage Package

7.3 Ghost Node Correction Package and Xt3D Option

7.3.1 The Ghost Node Correction Package
7.3.2 The XT3D Option

8 BOUNDARY CONDITIONS

8.1 Specified Heads: The Constant Head Package

8.2 Specified Flows

8.2.1 The Well Package
8.2.2 The Recharge Package

8.3 Head-Dependent Boundaries: Drain, River, and General Head Boundaries

8.3.1 Cell Size and Conductance

8.4 The Evapotranspiration Package

8.5 Opportunities to Learn More by Working with Modflow Models

9 OTHER PACKAGES

9.1 The Iterative Model Solution Package

9.2 The Output Control Option

9.3 The Streamflow Routing Package

9.4 The Horizontal Flow Barrier Package

10 TIME-VARIABLE INPUT

10.1 Time Series Files

10.2 Time Array Series Files

11 OBSERVATION UTILITY

12 ADVANCED PACKAGES

12.1 Skeletal Storage, Compaction, and Subsidence (CSUB) Package

12.2 Multi Aquifer Well (MAW) Package

12.3 Lake (LAK) Package

12.4 Unsaturated Zone Flow (UZF) Package

12.5 Water Mover (MVR) Package

12.6 Buoyancy (BUY6) Package

12.7 Viscosity (VSC) Package

12.8 Time-Varying Hydraulic Conductivity (TVK) And Time-Varying Storage (TVS) Packages

12.9 Groundwater Flow (GWF) Exchange Package

13 NEXT STEPS

14 EXERCISES

15 REFERENCES

16 BOXES

BOX 1 Some Details of How Modflow 6 Works

BOX 2 Contents of the Modflow 6 Distribution Folder

BOX 3 Test Your Knowledge of Structured Grids

BOX 4 Effect of Time Step Size on Model Accuracy

BOX 5 Step by Step Instructions, Model PS1A

BOX 6 Step-by-Step Instructions for Using Zonebudget With Model PS1A

BOX 7 Step by Step Instructions for Model Ps1B1

BOX 8 Step by Step Instructions for Model PS1B2

BOX 9 Step by Step Instructions for Model PS1B3

BOX 10 Step by Step Instructions for Model PS1B4

BOX 11 Step by Step Instructions for PS2A

BOX 12 Step by Step Instructions for PS2B

BOX 13 Step by Step Instructions for PS2C

BOX 14 Step by Step Instructions for PS2C1

BOX 15 Step by Step Instructions for PS2D

BOX 16 Step by Step Instructions for PS2D1

BOX 17 Step by Step Instructions for PS3BASE

BOX 18 Step by Step Instructions for PS3A

BOX 19 Step by Step Instructions for PS3B

BOX 20 Step by Step Instructions for PSMP

BOX 21 Step by Step Instructions for PSMP, Simulation 1

BOX 22 Step by Step Instructions for PSMP, Simulation 2

BOX 23 Step by Step Instructions for PSMP, Simulation 3

17 EXERCISE SOLUTIONS

18 ABOUT THE AUTHOR