Introduction to MODFLOW

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Introduction to MODFLOW
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Versions of MODFLOW

• MODFLOW
• MODFLOW-88
• MODFLOW-96
• MODFLOW-2000
• MODFLOW-2005

This class will use the documentation for
MODFLOW-2005 as a primary reference. Class
projects will be done with this version. The
report and program can be downloaded to your
computer from USGS web site
http//water.usgs.gov/nrp/gwsoftware/modflow2005/m
odflow2005.html
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MODFLOW-2005 Documentation

• Techniques and Methods 6-A16
• MODFLOW-2005, the U.S. Geological Survey
  modular ground-water model the Ground-Water
  Flow Process by Arlen Harbaugh
• Concepts,
• Input instructions, and
• Programmer guide for the core packages
• Replaces TWRI 6-A1, MODFLOW-96, and MODFLOW-2000
  reports
• There will continue to be separate reports for
  additional packages

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MODFLOW-2005 is an updated version of MODFLOW-2000

• Structural changes to support Local Grid
  Refinement (LGR)
• LGR will be discussed later
• Structural Enhancements also facilitate
  interfacing with other models
• E.g. GSFLOW (PRMS coupled to MODFLOW) being
  developed by Prudic, Niswonger, Leavesley, and
  Markstrom
• E.g. GWM, GWT, and SEAWAT

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MODFLOW-2005 is an updated version of MODFLOW-2000

• Uses parameter structure to ease the modification
  of data input values.
• Provides expanded data input capabilities.
• Program is designed to minimize changes that
  would impact existing MODFLOW users.

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Design objectives and how they were met

• Portable run on all computers with minimal
  modification
• Strict adherence to FORTRAN standards
• Easy to understand
• Modular program structure
• Modular data input
• Modules transfer data via subroutine arguments
  rather than through COMMON
• Documentation is modular
• Concepts are separated from the programming, but
  linked

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Design objectives and how they were met

• Easy to enhance
• Either by modifying the model program
• Modular structure
• Method of equation formulation using conductance,
  RHS, and HCOF
• Or by using with other programs (Pre and post
  processors)
• Flexible I/O
• Efficient
• FORTRAN
• Solvers use one-dimensional arrays

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Parameter Estimation

• Parameter Estimation is removed from MODFLOW-2005
• Separate programs will provide Parameter
  Estimation
• A new version of UCODE is on the web
• Observations are included in MODFLOW-2005
• Sensitivity is removed for now
• UCODE provides the capability to compute
  sensitivities using perturbation
• Sensitivity will be added again to MODFLOW-2005
  in the future

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Should MODFLOW-2000 Users Switch to MODFLOW-2005?

• No need to switch until you need some new
  functionality for example
• LGR
• New parameter estimation functionality
• PRMS-MODFLOW
• Same input files will work
• GLOBAL file is no longer allowed
• All output goes to LIST file
• Programs such as UCODE and GWM will include a
  file that serves the purpose of the former
  MODFLOW-2000 GLOBAL file
• The modflow.bf batch file capability is no
  longer supported
• .BAT files can be used to obtain this
  functionality.

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MODFLOW 2005 PROCESSES

• Previous MODFLOW tasks (prior to MF2K) are now
  defined as the
• Global Process
• GLO Controls Overall Program Operation
• Equation Solving Processes
• GWF Ground-water Flow Process

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MODFLOW 2005 PROCESSES

• As Initially released, MODFLOW also includes
  other processes
• OBS - Observation Process
• SEN - Sensitivity Process
• PES - Parameter Estimation Process
• GWT - Ground-water Transport Process
• Other Processes being developed including
• FMP Farm Process
• We are going to concentrate on the GWF
  Ground-water Flow Process and discuss the others
  later in the class

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GLOBAL PROCESS

• Controls overall program flow
• Activates capabilities (Packages)
• Opens package data files (Input and Output)
• Reads data for space and time discretization (DIS
  file)
• Reads parameter files (Multplier and Zone)
• Has a global level listing file
• The Global Process does not solve an equation

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GROUNDWATER FLOW PROCESS(abbreviated list)

• GWF Process Packages User Prospective
• BAS6 Basic Package
• Hydrologic Packages
• BCF6 Block Centered Flow Package
• LPF Layer Property Flow Package
• RCH Recharge Package
• RIV River Package
• WEL Well Package
• DRN Drain Package
• GHB General Head Boundary Package
• EVT Evapotranspiration Package
• STR Stream/Aquifer Package
• HFB6 Horizontal Flow Barrier Package
• CHD Constant-Head Package
• Solution Packages
• SOR Slice-Successive Over-relaxation
• SIP Strongly Implicit Procedure
• PCG Preconditioned Conjugate Gradient

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MODFLOW-2005 will evolve

• Initial ground-water flow capabilities
• BCF, LPF, HUF,HFB,CHD,RIV, WEL, DRN, GHB, RCH,
  EVT, STR, MNW, FHB, IBS,SIP, PCG, GMG, DE4
• Recently added capabilities
• ETS, DRT, RES, SUB, LAK, SFR, GAG, UZF
• New options in LPF
• CONSTANTCV (keeps CV constant)
• NOCVCORRECTION (does not apply vertical flow
  correction)
• STORAGECOEFFFICIENT (does not multiply SS by
  thickness)
• THICKSTART (computes thickness based on initial
  head)

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GROUNDWATER FLOW PROCESS

• GWF Process Procedures Programmer Prospective
• DF Define
• AL Allocate
• RP Read and Prepare
• ST Stress
• AD Advance
• FM Formulate
• AP Solve Equations
• OC Output Control
• BD Calculate Water Budget
• OT Output

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GROUNDWATER FLOW PROCESS Primary Modules

• Example RIV6FM
• The first three characters designate the package
  (river)
• The fourth character is the version number (6)
• The last two characters represent the procedure
  (formulate)

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Example Module Flowchart And Code
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MODFLOW user perspective

• Input Data
• ASCII text files
• Output Data
• ASCII text files
• Binary files
• Graphical user interface (GUI)
• Code Execution

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MODFLOW user perspective

• BASIC INPUT ITEMS
• Grid
• Time stepping
• Solution parameters
• Hydraulic parameters (includes material
  properties)
• Boundary Conditions
• Stresses (source-sinks)
• Output options
• BASIC OUTPUT ITEMS
• Hydraulic Heads
• Drawdown
• Flow rates
• Mass Balance
• Optional info at specified times
• Iteration information
• Binary files containing heads, drawdowns and flow
  rates in compressed form

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GUI

• Allows you to develop a nice image of model
  features on the computer screen and manipulate
  the model inputs graphically
• Creates the text files and executes MODFLOW.
• You never need to see the text files or know the
  commands that are necessary to run MODFLOW ...
  until something goes wrong!

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GUI

• Pros and Cons
• Inevitably something does not work correctly
• Need to have the ability to look at and
  understand the content of the model files and
  control the commands.
• Likely to dislike the tedium associated with the
  portion of the course where we work with text
  files

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File formats

• Original code MODFLOW88 expects to have FORMATTED
  DATA SETS
• exact about placement of data in columns of the
  file
• Occasionally see files in an old format (may have
  no spaces)
• MODFLOW96 provides the option of using either
  FREE or FORMATTED DATA SETS
• Translator was released with MODFLOW-2000
• Takes MODFLOW88 or MODFLOW96 files and convert
  them to MODFLOW-2000/2005
• HUF package allows geometry of the geology
  defined separately from the layers and have code
  simplify it to individual values for each model
  cell

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File formats

• Prior to MODFLOW-2000, MODFLOW required a
  different number in each model cell, now have
  flexibility in populating the cells with
  parameter values
• Parameters
• MODFLOW calculates value for each cell based on
• Parameter file (PVAL) defines values used to
  replace parameters specified in the files where
  parameters are defined (can use SEN in 2000)
• Multiplier files (MULT) - specify multiplier
  arrays which can be used to calculate layer
  variables
• Zone files (ZONE) specify the cells in a layer
  (arrays) that are associated with a parameter

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Next LEARNING MODFLOW

• Global Process
• Overview of Common Packages
• Basic
• Utility Module
• Output Control
• BCF
• WEL
• RIV
• RCH
• EVT
• STR
• DRN
• GHB
• LPF
• Once use to input for several packages, others
  are the same
• Best way to learn is to build a model
• In class, we will build a model for a simple
  problem
• Work on class project

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GLOBAL PROCESS DATA

• Name File Contains the names of most input and
  output files and controls the parts of the model
  program that are active.
• Discretization File Contains data that defines
  the physical size of the finite difference grid
  and the fundamental components of time
  discretization.
• Multiplier File Contains data to define
  multiplier arrays.
• Zone File Contains data to define zone arrays.

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NAME FILEContains the names of most input and
output files and controls the parts of the model
program that are active.
Example Name File twri.nam

• For each simulation, in free format
• Ftype Nunit Fname
• Ftypeis the file type with special character
  values. It is not case specific.
• Nunitis the Fortran unit to be used when reading
  from or writing to a file.
• Fnameis the name of the file. Pathnames maybe
  specified.

Name File is read on unit 99. Comments are
indicated by the character in column 1.
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FTYPE

• Basically key words that are fixed
• List for the forward run listingif this file
  is not present, the Global file is used for the
  forward run listing as well as for the global
  listing
• The GLOBAL FILE was only supported in
  MODFLOW-2000. In MODFLOW-2005, all of the listing
  is in the LIST file.
• It must be the first non-comment record.

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FTYPE CONTINUED

• Global Process Files
• DIS Discretization
• MULT Multiplier Array
• ZONE Zone Array
• GWF Process Packages
• BAS6 Basic
• OC Output Control
• BCF6 Block-Centered Flow
• LPF Layer Property Flow
• HFB6 Horizontal Flow Barrier
• RCH Recharge
• RIV River
• WEL Well

• DRN Drain
• GHB General-Head Boundary
• EVT Evapotranspiration
• STR Stream-Aquifer
• CHD Constant-Head
• GWF Solvers Packages
• SIP Strongly Implicit Procedure
• SOR Slice-Successive Over- Relaxation
• PCG Preconditioned Conjugate Gradient
• DE4 Direct Solution

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FTYPE CONTINUED

• Data Files
• DATA(BINARY) A binary (unformatted) file such as
  those used to save
• cell-by-cell budget data. Rewound for
  parameter estimation
• DATA A formatted (text) file such as those used
  to save heads and drawdown, and for input of
  data from files that are separate from primary
  package input files. Rewound for parameter
  estimation.
• Data Files For Parameter estimation (we probably
  wont use these)
• DATAGLO(BINARY) A binary file (unformatted)Not
  rewound
• DATAGLO A formatted (text) fileNot
  rewound

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DISCRETIZATION FILEContains data that defines
the physical size of the finite difference grid
and the fundamental components of time
discretization.

• All discretization data in one place
• Elevations always included even if GWF does not
  need because there is a good chance other
  processes will need it
• Not always included originally in order to save
  memory

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DISCRETIZATION FILEContains data that defines
the physical size of the finite difference grid
and the fundamental components of time
discretization.

• Horizontal Discretization
• Columns are numbered starting from the left side
  of the grid
• Rows are numbered starting from upper edge of
  grid
• Horizontal grid dimensions are specified in
  variables DELR and DELC.
• All cells in a column have the same width so
  there is one value of DELR for each of the
  columns.
• There is one value of DELC for each of the rows

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DISCRETIZATION FILE CONTINUED

• Vertical Discretization
• Layers are numbered from the top layer down.
• Elevation of the top of layer 1 is defined in
  addition to the bottom elevation of every layer.
• Cell thickness is calculated from the elevation
  information.
• Below each layer, except for the bottom layer,
  there may be a confining unit where only vertical
  flow is treated (Quazi 3d).
• For the confining units, the elevation of the
  bottom of bed is defined.

For each layer, the present or absents of a
quazi-3D confining bed must be indicated (LAYCBD).
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DISCRETIZATION FILE CONTINUED

• Time Discretization
• The fundamental component of time is the time
  step.
• Time steps are grouped into stress periods.
• Time dependent input data can be changed every
  stress period.
• Specified by user each stress
• period
• PERLEN Length of stress period
• TSMULT Time step multiplier
• NSTP Number of time steps in a stress
  period

If TSMULTgt1, the length of the first time step
(?t1) is determined from the following equation
for a geometric series
And for 2mNSTP,
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DISCRETIZATION FILE CONTINUED

• MODFLOW can simulate steady state (SS) or
  transient conditions (TR).
• A single stress period length is specified for
  steady state and only a single time step is
  required.
• Individual stress periods in a single simulation
  maybe either steady state or transient.
• The steady state and transient stress periods can
  occur in any order.

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DISCRETIZATION FILE CONTINUED

• Within the listing outputs, units of length and
  time may be labeled
• ITMUNI indicates the time label
• 0 undefined 3 hours
• 1 seconds 4 days
• 2 - minutes 5 years
• LENUNI indicates the length label
• 0 undefined 2 - meters
• 1 - feet 3 centimeters
• Note Be sure to use consistent units for all
  input data!

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DISCRETIZATION FILE CONTINUED

• Spatial
• NROW Number of rows
• NCOL Number of columns
• NPER Number of stress periods
• ITMUNI Time unit
• LENUNI Length unit
• LAYCBD Quazi 3D confining layer indicator. There
  is one value for each layer.
• LAYCON 1?Confining unit
• LAYCON0?No confining unit
• DELR Cell width along the row, there is one
  value for each NCOL columns. This data is read
  using a utility package (U1DREL)

Discretion File Data
Discretion File Data Example
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DISCRETIZATION FILE CONTINUED

• DELC Cell width along the columns, there is one
  value for each NROW rows. This data is read
  using a utility package (U1DREL)
• Top Top elevation for Layer 1. This data is
  read using a utility package (U2DREL)
• BOTM The bottom elevation. There is one for each
  layer and quazi 3D confining layer. This data
  is read using a utility package (U2DREL)

Discretion File Data
Discretion File Data Example
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DISCRETIZATION FILE CONTINUED

• Temporal
• PERLEN The length of a stress period
• NSTP Number of time steps in a stress period
• TSMULT Multiplier for the length of successive
  time steps
• Ss/Tr Is a character variable that indicates if
  a stress period is transient or steady state,
• TR Transient
• SS Steady State
• Note The four temporal variables are read for
  each stress period.

Discretion File Data
Discretion File Data Example
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Data to Define Terms for the Flow Equation

• Arrays one value for every cell in one or more
  layers
• Example Hydraulic Conductivity, Initial Head
• Lists one or more values at cells that are
  identifed by layer, row, and column
• Example Wells, Streams
• Methods of defining data
• Values directly read from files
• Values constructed from parameters

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PARAMETERS

• Generic meaning of PARAMETER
• Any input data for a model
• Meaning of PARAMETER IN MODFLOW-2005
• A specially designed value that can define input
  values for many cells
• Changing the parameter value changes all of the
  associated input values
• Parameters are used in the Parameter-Estimation
  Process because there is not enough data to
  estimate all types of inputs for all cells.
• Parameters are a convenient way to specify input
  data even if not using the Parameter-Estimation
  process.

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PARAMETER DEFINITION

• Parameters can only be specified for part of the
  input data
• LPF, CHD, GHB, RIV, DRN, WEL, RCH, EVT, HFB allow
  parameters
• Array parameters
• For each layer, specify multiplier and zone
  arrays
• NONE is a special multiplier array
• ALL is a special zone array
• If an array is defined using parameters, values
  for all cells in all layers must be defined by
  the parameters i.e. cannot define values for
  some cells using parameters and some without
  using parameters
• Additive parameters
• List parameters
• Can mix parameters with non-parameter data
• Additive parameters

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PARAMETERS

• Layer or Array Data
• A value is required for every cell in one or more
  horizontal of the grid (e.g. hydraulic
  conductivity)
• Data can either be read using the utility modules
  or using parameters, but the same method must be
  used consistently for any data type (e.g. if
  parameters are used to define hydraulic
  conductivity in a layer, then parameters must be
  used to define hydraulic conductivity for all the
  layers).

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PARAMETERS

• List Data
• One or more values at cells that are identified
  by layer, row, and column (examples wells,
  stream cells)
• Data values are required for only some of the
  cells (e.g. cell that have river nodes).
• MODFLOW-2005 allows only some list data to be
  defined using parameters (e.g. streambed
  conductance, but not stage or river bottom
  elevation).
• Parameters can be used, or one line of data can
  be read for each cell for which the data is
  required.
• It is generally possible to define some values in
  the list by directly reading and other values in
  the same list through parameters.

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PARAMETERS

• When parameters are used for list data, the data
  value for the cell is calculated as the product
  of the parameter value, which may apply to many
  cells, and a cell multiplier or factor, which
  applies only to the cell.

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PARAMETERS

• When parameters are used for array data,
  multipliers are defined using multiplier arrays.
• There may be a different multiplier array for
  each layer and each parameter type .
• If a specific parameter type has more than one
  parameter values for a layer, a zone array is
  used to assign specific values to specific cells.
• There can be a different zone array for each
  layer and each parameter type.

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PARAMETERS

• The data value in a cell can be determined by
  more than one parameter.
• If two or more parameters of the same type
  include the same cell, the final data value
  equals the sum of the contributions for all of
  the parameters.
• When two or more parameters are used to define
  the value for cells, the parameters are said to
  be additive.

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PARAMETERS
Multiplier Array for P1

• Example Use of two parameters to determine layer
  data values for the same cells.
• It is desired to have a hydraulic conductivity
  distribution (layer data) vary linearly from 10
  to 100 from the left side to the right side.
• Let P1 and P2 be the two parameters with
  multiplier arrays shown on the right.

Multiplier Array for P2
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PARAMETERS
P110 and P2100

• The contributions from both parameters will be
  added as indicated in the upper right table.
• The final result is shown in the lower right
  table.
• Note The same distribution could have been
  created other ways.

Final Result
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PARAMETERS
Parameter P1 Data List

• Example Use of two parameters to determine list
  data values for the same cells.
• Streambed conductance is assumed to be a mixture
  of two types of material coarse grained (P1) and
  fine grained (P2)
• Parameters P1 and P2 both include the five cells
  where the two river bed materials are intermixed.

Parameter P2 Data List
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MULTIPLIER FILE

• TEXT
• The character in column 1 and any type of
  characters there after up to 199 in number. Used
  for comments.
• NML
• The number of multiplier arrays to be defined.
• MLTNAM
• Name of multiplier array. May be up to 10
  characters in length and is not case sensitive.
• FUNCTION
• Optional keyword indicating that a multiplier
  array will be constructed from other multiplier
  arrays.

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MULTIPLIER FILE

• RMLT(NCOL,NROW) U2DREL
• The multiplier array.
• MLTNAM1, MLTNAM2, MLTNAM3
• Are names of the multiplier arrays that have
  already been defined.
• Op1, op2, op3
• Are arithmetic operators used to define a
  multiplier array based other multiplier arrays.
  The operators , -, and / are allowed.

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MULTIPLIER FILE
Example Multiplier Array Input Using FUNCTION
keyword
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ZONE FILE

• NZN
• The number of zone arrays to be defined.
• ZONNAM
• The name of a zone array May be up to 10
  characters in length and is not case sensitive.
• IZON(NCOL,NROW) U2DINT
• A zone name.

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ZONE FILE
Zone File Example