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Introduction to Groundwater Modelling - PDF

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					Introduction to Groundwater Modelling
                 C. P. Kumar
                         Scientist ‘F’

              National Institute of Hydrology
             Roorkee – 247667 (Uttaranchal)
                          India


               Email: cpkumar@yahoo.com
      Webpage: http://www.angelfire.com/nh/cpkumar/
Presentation Outline
 Groundwater in Hydrologic Cycle
 Why Groundwater Modelling is needed?
 Mathematical Models
 Modelling Protocol
 Model Design
 Calibration and Validation
 Groundwater Flow Models
 Groundwater Modelling Resources
Groundwater in Hydrologic Cycle
Types of Terrestrial Water

                Surface
                 Water




                                 Soil
                               Moisture




                Ground water
    Pores Full of Combination of Air and Water
      Unsaturated Zone / Zone of Aeration / Vadose
                     (Soil Water)




                    Zone of Saturation (Ground water)

Pores Full Completely with Water
                       Groundwater


Important source of clean water
   More abundant than SW




            Baseflow              Linked to SW systems

                                     Sustains flows
                                       in streams
            Groundwater Concerns?



pollution




             groundwater mining
                 subsidence
Problems with groundwater
 Groundwater overdraft / mining / subsidence

 Waterlogging

 Seawater intrusion

 Groundwater pollution
Why Groundwater Modelling is needed?
Groundwater

•   An important component of water resource systems.

•   Extracted from aquifers through pumping wells and
    supplied for domestic use, industry and agriculture.

•   With increased withdrawal of groundwater, the quality
    of groundwater has been continuously deteriorating.

•   Water can be injected into aquifers for storage and/or
    quality control purposes.
    Management of a groundwater system, means
    making such decisions as:

•   The total volume that may be withdrawn annually from the aquifer.

•   The location of pumping and artificial recharge wells, and their
    rates.

•   Decisions related to groundwater quality.


    Groundwater contamination by:

    Hazardous industrial wastes

    Leachate from landfills

    Agricultural activities such as the use of fertilizers and pesticides
MANAGEMENT means making decisions to achieve goals without
violating specified constraints.

Good management requires information on the response of the
managed system to the proposed activities.

This information enables the decision-maker, to compare alternative
actions and to ensure that constraints are not violated.

Any planning of mitigation or control measures, once contamination
has been detected in the saturated or unsaturated zones, requires
the prediction of the path and the fate of the contaminants, in
response to the planned activities.

Any monitoring or observation network must be based on the
anticipated behavior of the system.
A tool is needed that will provide this information.

The tool for understanding the system and its behavior
and for predicting this response is the model.

Usually, the model takes the form of a set of
mathematical equations, involving one or more partial
differential equations. We refer to such model as a
mathematical model.

The preferred method of solution of the mathematical
model of a given problem is the analytical solution.
The advantage of the analytical solution is that the
same solution can be applied to various numerical
values of model coefficients and parameters.

Unfortunately, for most practical problems, because of
the heterogeneity of the considered domain, the
irregular shape of its boundaries, and the non-analytic
form of the various functions, solving the mathematical
models analytically is not possible.

Instead, we transform the mathematical model into a
numerical one, solving it by means of computer
programs.
Prior to determining the management scheme for any aquifer:

 We should have a CALIBRATED MODEL of the aquifer, especially,
 we should know the aquifer’s natural replenishment (from
 precipitation and through aquifer boundaries).

 The model will provide the response of the aquifer (water levels,
 concentrations, etc.) to the implementation of any management
 alternative.
 We should have a POLICY that dictates management objectives
 and constraints.
 Obviously, we also need information about the water demand
 (quantity and quality, current and future), interaction with other
 parts of the water resources system, economic information, sources
 of pollution, effect of changes on the environment---springs, rivers,...
      GROUND WATER MODELING

              WHY MODEL?

•To make predictions about a ground-water
 system’s response to a stress

•To understand the system

•To design field studies

•Use as a thinking tool
    Use of Groundwater models
•   Can be used for three general purposes:
•   To predict or forecast expected artificial
    or natural changes in the system.
    Predictive is more applied to deterministic
    models since it carries higher degree of
    certainty, while forecasting is used with
    probabilistic (stochastic) models.
    Use of Groundwater models
•   To describe the system in order to analyse
    various assumptions
•   To generate a hypothetical system that
    will be used to study principles of
    groundwater flow associated with various
    general or specific problems.
ALL GROUND-WATER HYDROLOGY WORK IS MODELING

      A Model is a representation of a system.

 Modeling begins when one formulates a concept of a
                 hydrologic system,
     continues with application of, for example,
            Darcy's Law to the problem,
                      and may
    culminate in a complex numerical simulation.
Ground Water Flow Modelling

                      A Powerful Tool
             for furthering our understanding
               of hydrogeological systems



    Importance of understanding ground water flow models
      Construct accurate representations of hydrogeological systems
      Understand the interrelationships between elements of systems
      Efficiently develop a sound mathematical representation
      Make reasonable assumptions and simplifications
      Understand the limitations of the mathematical representation
      Understand the limitations of the interpretation of the results
Introduction to Ground Water Flow Modelling

                      Predicting heads (and flows) and
                        Approximating parameters
                                                                             h(x,y,z,t)?
                                                            Poten
    Solutions to the flow equations                              tiome
                                                                       tri
       Most ground water flow models are                          Surfa c
                                                                        ce
       solutions of some form of the ground
       water flow equation
                                                                                      x
       The partial differential equation needs
       to be solved to calculate head as a                              q
       function of position and time,                       K
       i.e., h=f(x,y,z,t)
                                                            ho x
       “e.g., unidirectional, steady-state flow                        x h(x)
                                                                                x
       within a confined aquifer
        Darcy’s Law           Integrated                        0               x
         dh    q          h        q       x                   qx                     qx
         dx
            =−
               K
                 ⇒      ∫h0 dh = − K   ∫   0
                                               dx ⇒ h − h0 = −
                                                               K
                                                                      h( x ) = h0 −
                                                                                      K
    Groundwater Modeling
The only effective way to test effects of
groundwater management strategies
Takes time, money to make model
Conceptual model
    Steady state model
          Transient model
The model is only as good as its calibration
   Processes we might want to model


• Groundwater flow
  calculate both heads and flow


• Solute transport – requires information
  on flow (velocities)
   calculate concentrations
                MODELING PROCESS




ALL IMPORTANT MECHANISMS & PROCESSES MUST BE INCLUDED IN
          THE MODEL, OR RESULTS WILL BE INVALID.
TYPES OF MODELS
 CONCEPTUAL MODEL QUALITATIVE DESCRIPTION OF SYSTEM
 "a cartoon of the system in your mind"

 MATHEMATICAL MODEL MATHEMATICAL DESCRIPTION OF
 SYSTEM

 SIMPLE - ANALYTICAL (provides a continuous solution over the
 model domain)

 COMPLEX - NUMERICAL (provides a discrete solution - i.e. values are
 calculated at only a few points)

 ANALOG MODEL e.g. ELECTRICAL CURRENT FLOW through a
 circuit board with resistors to represent hydraulic conductivity and
 capacitors to represent storage coefficient

 PHYSICAL MODEL e.g. SAND TANK which poses scaling problems
Mathematical Models
Mathematical model:

 simulates ground-water flow and/or
 solute fate and transport indirectly by
 means of a set of governing equations
 thought to represent the physical
 processes that occur in the system.

 (Anderson and Woessner, 1992)
Components of a Mathematical Model

• Governing Equation
(Darcy’s law + water balance equation)
with head (h) as the dependent variable
• Boundary Conditions
• Initial conditions (for transient problems)
        Derivation of the Governing Equation


     R Δx Δy                              Q


                         q



Δz

                  Δx
          Δy
                       1. Consider flux (q) through REV
                       2. OUT – IN = - ΔStorage
                       3. Combine with: q = -K grad h
  Law of Mass Balance + Darcy’s Law =
  Governing Equation for Groundwater Flow
---------------------------------------------------------------

   div   q = - Ss (∂h ⁄∂t)      (Law of Mass Balance)

     q = - K grad h                      (Darcy’s Law)


             div (K grad h) = Ss (∂h ⁄∂t)
                                                (Ss = S / Δ z)
         General governing equation
 for steady-state, heterogeneous, anisotropic
     conditions, without a source/sink term

∂      ∂h   ∂      ∂h   ∂      ∂h
   ( Kx ) +    ( Ky ) +    ( Kz ) = 0
∂x     ∂x   ∂y     ∂y   ∂z     ∂z


         with a source/sink term

∂      ∂h   ∂      ∂h   ∂      ∂h
   ( Kx ) +    ( Ky ) +    ( Kz ) = − R *
∂x     ∂x   ∂y     ∂y   ∂z     ∂z
General governing equation for transient,
heterogeneous, and anisotropic conditions


∂      ∂h   ∂      ∂h   ∂       ∂h      ∂h
   ( Kx ) +    ( Ky ) +    ( K z ) = Ss    − R*
∂x     ∂x   ∂y     ∂y   ∂z      ∂z      ∂t


                        Specific Storage
                        Ss = ΔV / (Δx Δy Δz Δh)
                          Δh
Δh

                                                      b



                    S=V/AΔh
                     S = Ss b Confined aquifer
 Unconfined aquifer
  Specific yield               Storativity

                               Figures taken from Hornberger et al. (1998)
   General 3D equation
    ∂      ∂h   ∂      ∂h   ∂       ∂h      ∂h
       ( Kx ) +    ( Ky ) +    ( K z ) = Ss    − R*
    ∂x     ∂x   ∂y     ∂y   ∂z      ∂z      ∂t


                      ∂      ∂h   ∂      ∂h     ∂h
 2D confined:            (T x ) +    (T y ) = S    −R
                      ∂x     ∂x   ∂y     ∂y     ∂t


2D unconfined:         ∂        ∂h   ∂        ∂h     ∂h
                          ( hK x ) +    ( hK y ) = S    −R
                       ∂x       ∂x   ∂y       ∂y     ∂t


  Storage coefficient (S) is either storativity or specific yield.
                       S = Ss b & T = K b
Types of Solutions of Mathematical Models

• Analytical Solutions: h= f(x,y,z,t)
  (example: Theis equation)

• Numerical Solutions
    Finite difference methods
    Finite element methods

• Analytic Element Methods (AEM)
Limitations of Analytical Models

The flexibility of analytical modeling is
limited due to simplifying assumptions:
    Homogeneity, Isotropy, simple geometry,
    simple initial conditions…


Geology is inherently complex:
    Heterogeneous, anisotropic, complex
    geometry, complex conditions…




This complexity calls for a more
powerful solution to the flow equation        Numerical modeling
       Numerical Methods
hAll numerical methods involve
 representing the flow domain by a
 limited number of discrete points called
 nodes.
hA set of equations are then derived to
 relate the nodal values of the
 dependent variable such that they
 satisfy the governing PDE, either
 approximately or exactly.
• Numerical Solutions

 Discrete solution of head at selected nodal points.
 Involves numerical solution of a set of algebraic
 equations.


 Finite difference models (e.g., MODFLOW)
 Finite element models (e.g., SUTRA)
             Finite Difference Modelling


3-D Finite Difference Models
  Requires vertical discretization (or layering) of model


 K1
 K2
 K3
 K4
    Finite difference models
     may be solved using:

• a computer program
  (e.g., a FORTRAN program)

• a spreadsheet (e.g., EXCEL)
Finite Elements: basis functions, variational principle,
                    Galerkin’s method, weighted residuals

  • Nodes plus elements; elements defined by nodes

  • Properties (K, S) assigned to elements

  • Nodes located on flux boundaries
  • Able to simulate point sources/sinks at nodes
  • Flexibility in grid design:
      elements shaped to boundaries
      elements fitted to capture detail

   • Easier to accommodate anisotropy that occurs at an
     angle to the coordinate axis
Hybrid

Analytic Element Method (AEM)
Involves superposition of analytic solutions. Heads are
calculated in continuous space using a computer to do
the mathematics involved in superposition.

The AE Method was introduced by Otto Strack.
A general purpose code, GFLOW, was developed by
Strack’s student Henk Haitjema, who also wrote a
textbook on the AE Method: Analytic Element Modeling
of Groundwater Flow, Academic Press, 1995.

Currently the method is limited to steady-state,
two-dimensional, horizontal flow.
Modelling Protocol
       What is a “model”?
Any “device” that represents approximation
to field system
  Physical Models
  Mathematical Models
    Analytical
    Numerical
 Modelling Protocol
Establish the Purpose of the Model
Develop Conceptual Model of the System
Select Governing Equations and Computer Code
Model Design
Calibration
Calibration Sensitivity Analysis
Model Verification
Prediction
Predictive Sensitivity Analysis
Presentation of Modeling Design and Results
Post Audit
Model Redesign
Purpose - What questions do you want the
model to answer?

   Prediction; System Interpretation; Generic
   Modeling
   What do you want to learn from the model?
   Is a modeling exercise the best way to
   answer the question? Historical data?
   Can an analytical model provide the answer?
       System Interpretation: Inverse Modeling: Sensitivity
        System Interpretation: Inverse Modeling: Sensitivity
       Analysis
        Analysis
       Generic: Used in aahypothetical sense, not necessarily
        Generic: Used in hypothetical sense, not necessarily
       for aareal site
        for real site
Model “Overkill”?

 Is the vast labor of characterizing the system,
 combined with the vast labor of analyzing it,
 disproportionate to the benefits that follow?
ETHICS
 There may be a cheaper, more effective
 approach
 Warn of limitations
ConceptualasModel but not simpler.” Albert
“Everything should be made simple as possible,
Einstein


      Pictorial representation of the groundwater
      flow system
      Will set the dimensions of the model and
      the design of the grid
      “Parsimony”….conceptual model has been
      simplified as much as possible yet retains
      enough complexity so that it adequately
      reproduces system behavior.
Select Computer Code
  Select Computer Model
  Code Verification
     Comparison to Analytical Solutions; Other
     Numerical Models
  Model Design
     Design of Grid, selecting time steps,
     boundary and initial conditions, parameter
     data set

 Steady/Unsteady..1, 2, or 3-D;
  Steady/Unsteady..1, 2, or 3-D;
 …Heterogeneous/Isotropic…..Instantaneous/Continuous
  …Heterogeneous/Isotropic…..Instantaneous/Continuous
Calibration
Show that Model can reproduce field-
measured heads and flow (concentrations if
contaminant transport)
Results in parameter data set that best
represents field-measured conditions.
Calibration Sensitivity Analysis
     Uncertainty in Input Conditions
     Determine Effect of Uncertainty on
     Calibrated Model
Model Verification
Use Model to Reproduce a Second Set of
Field Data


Prediction
Desired Set of Conditions
Sensitivity Analysis
  Effect of uncertainty in parameter values and
  future stresses on the predicted solution
Presentation of Modelling
Design and Results
        Effective Communication of
        Modeling Effort
          Graphs, Tables, Text etc.
Postaudit
 New field data collected to
 determine if prediction was correct
 Site-specific data needed to
 validate model for specific site
 application


Model Redesign
 Include new insights into system
 behavior
NUMERICAL MODELING

  DISCRETIZE

  Write equations of GW Flow between each node
                  Darcy's Law
                  Conservation of Mass

  Define         Material Properties
                 Boundary Conditions
                 Initial Conditions
                 Stresses

  At each node either H or Q is known, the other is unknown
                  n equations & n unknowns
                  solve simultaneously with matrix algebra

  Result         H at each known Q node
                 Q at each known H node

  Calibrate      Steady State
                 Transient

  Validate

  Sensitivity

  Predictions

  Similar Process for Transport Modeling only Concentration and Flux is unknown
NUMERICAL MODELING
Model Design
                  MODELs NEED

                    Geometry
      Material Properties (K, S, T, Φe, R, etc.)
Boundary Conditions (Head, Flux, Concentration etc.)

       Stress - changing boundary condition
               Model Design

•   Conceptual Model
•   Selection of Computer Code
•   Model Geometry
•   Grid
•   Boundary array
•   Model Parameters
•   Boundary Conditions
•   Initial Conditions
•   Stresses
       Concept Development
• Developing a conceptual model is the initial
  and most important part of every modelling
  effort. It requires thorough understanding
  of hydrogeology, hydrology and dynamics
  of groundwater flow.
Conceptual Model

A descriptive representation
of a groundwater system that
incorporates an interpretation of the
geological & hydrological conditions.
Generally includes information about
the water budget. May include
information on water chemistry.
   Selection of Computer Code
• Which method will be used depends largely
  on the type of problem and the knowledge of
  the model design.
• Flow, solute, heat, density dependent etc.
• 1D, 2D, 3D
           Model Geometry
• Model geometry defines the size and the
  shape of the model. It consists of model
  boundaries, both external and internal, and
  model grid.
               Boundaries
• Physical boundaries are well defined
  geologic and hydrologic features that
  permanently influence the pattern of
  groundwater flow (faults, geologic units,
  contact with surface water etc.)
              Boundaries
• Hydraulic boundaries are derived from the
  groundwater flow net and therefore
  “artificial” boundaries set by the model
  designer. They can be no flow boundaries
  represented by chosen stream lines, or
  boundaries with known hydraulic head
  represented by equipotential lines.
HYDRAULIC BOUNDARIES

            A streamline (flowline) is also a
            hydraulic boundary because by
            definition, flow is ALWAYS
            parallel to a streamflow. It can
            also be said that flow NEVER
            crosses a streamline; therefore it
            is similar to an IMPERMEABLE
            (no flow) boundary

            BUT

            Stress can change the flow
            pattern and shift the position of
            streamlines; therefore care must
            be taken when using a
            streamline as the outer boundary
            of a model.
TYPES OF MODEL BOUNDARY


          NO-FLOW BOUNDARY
          Neither HEAD nor FLUX is
          Specified. Can represent a
          Physical boundary or a flow
          Line (Groundwater Divide)



           SPECIFIED HEAD OR
           CONSTANT HEAD BOUNDARY
           h = constant
           q is determined by the model.
           And may be +ve or –ve according
           to the hydraulic gradient developed
TYPES OF MODEL BOUNDARY (cont’d)


                SPECIFIED FLUX BOUNDARY
                q = constant
                h is determined by the model
                (The common method of simulation
                is to use one injection well for each
                boundary cell)



                 HEAD DEPENDANT BOUNDARY
                 hb = constant
                 q = c (hb – hm)
                 and c = f (K,L) and is called
                 CONDUCTANCE
                 hm is determined by the model and
                 its interaction with hb
                       Boundary Types
Specified Head/Concentration: a special case of constant head (ABC, EFG)

Constant Head /Concentration: could replace (ABC, EFG)

Specified Flux: could be recharge across (CD)

No Flow (Streamline): a special case of specified flux (HI)

Head Dependent Flux: could replace (ABC, EFG)

Free Surface: water-table, phreatic surface (CD)

Seepage Face: pressure = atmospheric at ground surface (DE)
Boundary conditions in Modflow
• Constant head boundary
• Head dependent flux
   – River Package
   – Drain Package
   – General-head Boundary Package
• Known Flux
   –   Recharge
   –   Evapotranspiration
   –   Wells
   –   Stream
• No Flow boundaries
           Initial Conditions
• Values of the hydraulic head for each active
  and constant-head cell in the model. They
  must be higher than the elevation of the cell
  bottom.
• For transient simulation, heads to resemble
  closely actual heads (realistic).
• For steady state, only hydraulic heads in
  constant head-cell must be realistic.
          Model Parameters
• Time
• Space (layer top and bottom)
• Hydrogeologic characteristics
  (hydraulic conductivity, transmissivity,
  storage parameters and effective porosity)
                    Time
• Time parameters are specified when
  modelling transient (time dependent)
  conditions. They include time unit, length
  and number of time steps.
• Length of stress periods is not relevant for
  steady state simulations
                    Grid
• In Finite Difference model, the grid is
  formed by two sets of parallel lines that are
  orthogonal. The blocks formed by these
  lines are called cells. In the centre of each
  cell is the node – the point at which the
  model calculates hydraulic head. This type
  of grid is called block-centered grid.
                      Grid
• Grid mesh can be uniform or custom, a
  uniform grid is better choice when
  – Evenly distributed aquifer characteristics data
  – The entire flow field is equally important
  – Number of cells and size is not an issue
                      Grid
• Grid mesh can be custom when
  – There is less or no data for certain areas
  – There is specific interest in one or more smaller
    areas
• Grid orientation is not an issue in isotropic
  aquifers. When the aquifer is anisotropic,
  the model coordinate axes must be aligned
  with the main axes of the hydraulic
  conductivity.
•   Regular vs irregular grid spacing

    Irregular spacing may be used to obtain
    detailed head distributions in selected areas
    of the grid.


    Finite difference equations that use irregular
    grid spacing have a higher associated error
    than FD equations that use regular grid spacing.
Considerations in selecting the size of
the grid spacing

Variability of aquifer characteristics (K,T,S)

Variability of hydraulic parameters (R, Q)

Curvature of the water table

Vertical change in head

Desired detail around sources and sinks (e.g., rivers)
MODEL GRIDS
                  Grids
h It is generally agreed that from a practical
  point-of-view the differences between grid
  types are minor and unimportant.
h USGS MODFLOW employs a body-centred grid.
     Boundary array (cell type)
• Three types of cells
  – Inactive cells through which no flow into or out
    of the cells occurs during the entire time of
    simulation.
  – Active, or variable-head cells are free to vary
    in time.
  – Constant-head cell, model boundaries with
    known constant head.
    Hydraulic conductivity and
         transmissivity

• Hydraulic conductivity is the most critical
  and sensitive modelling parameter.
• Realistic values of storage coefficient and
  transmissivity, preferably from pumping test,
  should be used.
          Effective porosity

• Required to calculate velocity, used mainly
  in solute transport models
Calibration and Validation
Calibration parameters are uncertain parameters
whose values are adjusted during model calibration.



Identify calibration parameters and their reasonable
ranges.



Typical calibration parameters include hydraulic
conductivity and recharge rate.
In a real-world problem, we need to establish model
specific calibration criteria and define targets including
associated error.


                         Calibration Targets
                              associated error
            calibration
            value
                      +/−0.80 m
             20.24 m

                                          Target with smaller
                                          associated error.
      Target with relatively
      large associated error.
        Targets used in Model Calibration

• Head measured in an observation well is known
as a target.

• The simulated head at the node representing the
observation well is compared with the measured head.

• During model calibration, parameter values are
adjusted until the simulated head matches the observed
value.

• Model calibration solves the inverse problem.
        Calibration to Fluxes

When recharge rate (R) is a calibration
parameter, calibrating to fluxes can help in
estimating K and/or R.
In this example, flux information
helps calibrate K.

                               q = KI

H1
                              H2
In this example, discharge
information helps calibrate R.
            Calibration - Remarks

• Calibrations are non-unique.

• A good calibration does not ensure that
  the model will make good predictions.

• You can never have enough field data.

• Modelers need to maintain a healthy skepticism
  about their results.

• Need for an uncertainty analysis to accompany
  calibration results and predictions.
        Uncertainty in the Calibration

Involves uncertainty in:

     Targets

     Parameter values


     Conceptual model including boundary conditions,
     zonation, geometry etc.
        Ways to analyze uncertainty
            in the calibration

Sensitivity analysis is used as an uncertainty
analysis after calibration.


Use an inverse model (automated calibration)
to quantify uncertainties and optimize the
calibration.
      Uncertainty in the Prediction



Reflects uncertainty in the calibration.


Involves uncertainty in how parameter values
(e.g., recharge) will vary in the future.
  Ways to quantify uncertainty
       in the prediction



Sensitivity analysis


Stochastic simulation
How do we “validate” a model so that
we have confidence that it will make
accurate predictions?
        Modeling Chronology
1960’s Flow models are great!

1970’s Contaminant transport models are great!

1975   What about uncertainty of flow models?
1980s Contaminant transport models don’t work.
       (because of failure to account for heterogeneity)

1990s Are models reliable?
“The objective of model validation is to
determine how well the mathematical
representation of the processes describes
the actual system behavior in terms of the
degree of correlation between model
calculations and actual measured data”.
     How to build confidence in a model

Calibration (history matching)

“Verification”
        requires an independent set of field data

Post-Audit: requires waiting for prediction to occur

Models as interactive management tools
              KEEPING AN OPEN MIND

Consider all dimensions of the problem before coming
                  to a conclusion.

Considering all the stresses that might be imposed and
 all the possible processes that might be involved in a
         situation before reaching a conclusion.

  KEEPING AN OPEN MIND is spending 95% of your
TIME DETERMINING WHAT YOU THINK IS HAPPENING
and only 5% of your TIME DEFENDING YOUR OPINION.

   AVOID the common human TRAP of REVERSING
              THOSE PERCENTAGES.
Groundwater Flow Models
Groundwater Flow Models

•   The most widely used numerical groundwater flow model is
    MODFLOW which is a three-dimensional model, originally
    developed by the U.S. Geological Survey.
•   It uses finite difference scheme for saturated zone.
•   The advantages of MODFLOW include numerous facilities
    for data preparation, easy exchange of data in standard
    form, extended worldwide experience, continuous
    development, availability of source code, and relatively low
    price.
•   However, surface runoff and unsaturated flow are not
    included, hence in case of transient problems, MODFLOW
    can not be applied if the flux at the groundwater table
    depends on the calculated head and the function is not
    known in advance.
          MODFLOW

√ USGS code
√ Finite Difference Model

• MODFLOW 88
• MODFLOW 96
• MODFLOW 2000
MODFLOW

    (Three-Dimensional Finite-Difference Ground-Water Flow
    Model)
•   When properly applied, MODFLOW is the recognized
    standard model.
•   Ground-water flow within the aquifer is simulated in
    MODFLOW using a block-centered finite-difference
    approach.
•   Layers can be simulated as confined, unconfined, or a
    combination of both.
•   Flows from external stresses such as flow to wells, areal
    recharge, evapotranspiration, flow to drains, and flow
    through riverbeds can also be simulated.
MT3D

(A Modular 3D Solute Transport Model)


•   MT3D is a comprehensive three-dimensional numerical
    model for simulating solute transport in complex
    hydrogeologic settings.


•   MT3D is linked with the USGS groundwater flow simulator,
    MODFLOW, and is designed specifically to handle
    advectively-dominated transport problems without the need
    to construct refined models specifically for solute transport.
FEFLOW

(Finite Element Subsurface Flow System)

FEFLOW is a finite-element package for simulating 3D and 2D
fluid density-coupled flow, contaminant mass (salinity) and
heat transport in the subsurface.


HST3D

(3-D Heat and Solute Transport Model)

The Heat and Solute Transport Model HST3D simulates
ground-water flow and associated heat and solute transport in
three dimensions.
SEAWAT

(Three-Dimensional Variable-Density Ground-Water Flow)


•   The SEAWAT program was developed to simulate three-
    dimensional, variable- density, transient ground-water flow
    in porous media.

•   The source code for SEAWAT was developed by
    combining MODFLOW and MT3D into a single program
    that solves the coupled flow and solute-transport equations.
SUTRA

(2-D Saturated/Unsaturated Transport Model)


•   SUTRA is a 2D groundwater saturated-unsaturated
    transport model, a complete saltwater intrusion and energy
    transport model.

•   SUTRA employs a two-dimensional hybrid finite-element
    and integrated finite-difference method to approximate the
    governing equations that describe the two interdependent
    processes.

•   A 3-D version of SUTRA has also been released.
SWIM

(Soil water infiltration and movement model)

•   SWIMv1 is a software package for simulating water
    infiltration and movement in soils.
•   SWIMv2 is a mechanistically-based model designed to
    address soil water and solute balance issues.
•   The model deals with a one-dimensional vertical soil
    profile which may be vertically inhomogeneous but is
    assumed to be horizontally uniform.
•   It can be used to simulate runoff, infiltration,
    redistribution, solute transport and redistribution of
    solutes, plant uptake and transpiration, evaporation, deep
    drainage and leaching.
VISUAL HELP

    (Modeling Environment for Evaluating and Optimizing
    Landfill Designs)

•   Visual HELP is an advanced hydrological modeling
    environment available for designing landfills, predicting
    leachate mounding and evaluating potential leachate
    contamination.

Visual MODFLOW

    (Integrated Modeling Environment for MODFLOW and
    MT3D)

•   Visual MODFLOW provides professional 3D groundwater
    flow and contaminant transport modeling using
    MODFLOW and MT3D.
Groundwater Modelling Resources
Groundwater Modeling Resources
Kumar Links to Hydrology Resources
   http://www.angelfire.com/nh/cpkumar/hydrology.html

USGS Water Resources Software Page
   water.usgs.gov/software

Richard B. Winston’s Home Page
   www.mindspring.com/~rbwinston/rbwinsto.htm

Geotech & Geoenviron Software Directory
   www.ggsd.com

International Ground Water Modeling Center
   www.mines.edu/igwmc
Ground Water Modelling Discussion Group

An email discussion group related to ground water modelling and
analysis. This group is a forum for the communication of all aspects
of ground water modelling including technical discussions;
announcement of new public domain and commercial softwares; calls
for abstracts and papers; conference and workshop announcements;
and summaries of research results, recent publications, and case
studies.

Group home page   : http://groups.yahoo.com/group/gwmodel/
Post message      : gwmodel@yahoogroups.com
Subscribe         : gwmodel-subscribe@yahoogroups.com
Unsubscribe       : gwmodel-unsubscribe@yahoogroups.com
List owner         : gwmodel-owner@yahoogroups.com
Visual MODFLOW Users Group

Visual MODFLOW is a proven standard for professional 3D
groundwater flow and contaminant transport modeling using
MODFLOW-2000, MODPATH, MT3DMS AND RT3D. Visual
MODFLOW seamlessly combines the standard Visual MODFLOW
package with Win PEST and the Visual MODFLOW 3D-Explorer to give
a complete and powerful graphical modeling environment.

This group aims to provide a forum for exchange of ideas and
experiences regarding use and application of Visual MODFLOW
software.

Group home page   : http://in.groups.yahoo.com/group/visual-modflow/
Post message      : visual-modflow@yahoogroups.co.in
Subscribe         : visual-modflow-subscribe@yahoogroups.co.in
Unsubscribe       : visual-modflow-unsubscribe@yahoogroups.co.in
List owner         : visual-modflow-owner@yahoogroups.co.in
   THANKS




HAPPY MODELLING

				
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