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Introduction to MODFLOW

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Title: Conceptual Model Development Subject: Intro to Ground-Water Modeling with MODFLOW Author: Tom REilly, Herb Buxton, Eve Kuniansky, Keith Halford, Bruce Campbell – PowerPoint PPT presentation

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Title: Introduction to MODFLOW


1
Introduction to MODFLOW
2
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
3
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

4
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

5
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.

6
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

7
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

8
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

9
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.

10
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

11
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

12
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

13
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

14
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)

15
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

16
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)

17
Example Module Flowchart And Code
18
MODFLOW user perspective
  • Input Data
  • ASCII text files
  • Output Data
  • ASCII text files
  • Binary files
  • Graphical user interface (GUI)
  • Code Execution

19
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

20
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!

21
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

22
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

23
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

24
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

25
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.

26
NAME FILE Contains 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.
27
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.

28
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

29
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

30
DISCRETIZATION FILE Contains 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

31
DISCRETIZATION FILE Contains 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

32
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).
33
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,
34
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.

35
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!

36
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
37
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
38
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
39
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

40
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.

41
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

42
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).

43
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.

44
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.

45
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.

46
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.

47
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
48
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
49
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
50
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.

51
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.

52
MULTIPLIER FILE
Example Multiplier Array Input Using FUNCTION
keyword
53
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.

54
ZONE FILE
Zone File Example
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