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Define Modeling Objectives

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The first step in defining your conceptual model is to Define the Modeling Objectives, as shown below.  Modeling Objectives are divided into two sections:

 

Flow Objectives

Transport Objectives

 

 

 

 

Visual MODFLOW Flex supports numerous groundwater flow models developed by the USGS and others. For the purposes of clarity and to distinguish them from particular regional and site-specific models, these models are referred to as "engines".  Visual MODFLOW Flex currently supports the following engines:

 

Engines supported in Visual MODFLOW Flex

Flow

Transport

Utilities

 

MODFLOW-2000

MODFLOW-2005

MODFLOW-LGR

MODFLOW-NWT

MODFLOW-USG1

MODFLOW-SURFACT2

SEAWAT3

 

 

MT3DMS

RT3D

 

 

 

MODFLOW-SURFACT2

SEAWAT3

 

ZONEBUDGET and

MODPATH

 

Notes:

1 - MODFLOW-USG uses unstructured grids and is supported under a separate workflow process as compared to the standard numerical workflow.

2 - MODFLOW-SURFACT is a commercial groundwater modeling engine that supports coupled groundwater flow and transport simulations.

3 - SEAWAT is a coupled variable density groundwater flow and transport model

 

Flow Objectives

 

The first step in the workflow for developing and running numerical models in Visual MODFLOW Flex is to define the modeling objectives. This entails selecting the desired flow and transport simulation options.  The selected combination of flow options (e.g. saturated groundwater flow) and transport options (e.g. reaction and sorption models) will narrow the list of available flow and transport engines and generate associated input variables (including units and default values).  The purpose of this step is to develop the necessary inputs required to build the model based on your understanding of the relevant physical processes present within the study area.

 

The flow engines supported in Visual MODFLOW Flex are presented in the table below, which provides a preview of what engines are available based on your selected flow and simulation types.

 

Flow Engines and Modeling Objectives Supported in Visual MODFLOW Flex

Flow Type

Saturated Flow

Variably Saturated Flow1

 

Zone Budget

 

MODPATH

 

Transport

Simulation
 Type

Constant Density

Variable Density

Groundwater

Vapor Flow

UZF

V

BC

V

BC

Engines

 

 

 

MF-2000

 

 

 

 

 

 

MF-2005

 

 

 

 

 

MF-NWT

 

 

 

 

 

MF-LGR

 

 

 

 

 

 

 

 

MF-USG

 

 

 

 

 

 

 

 

SEAWAT

 

 

 

 

 

 

SEAWAT

MF-SURFACT

 

 

MF-SURFACT

Notes:

1 - Abbreviations for variably saturated flow processes in the Vadose Zone:

     UZF = unsaturated zone flow package is based on 1-D unsaturated flow of a diffusion wave pseudo soil

     V = Van Genuchten relative permeability and saturation relationship

     BC = Brooks-Corey relative permeability and saturation relationship

 

 

Under Property Settings, you can modify the default flow parameters.

 

MODFLOW-LGR & MODFLOW-USG and Transport

The MODFLOW-LGR and MODFLOW-USG flow engines do not currently support contaminant transport with MT3DMS or RT3D.

 

The Start Date of the model corresponds to the beginning of the simulation time period. It is important to define a relevant start date since your field measurements (observed heads and pumping schedules) will be defined with absolute (calendar) date measurements, and must lie within the simulation time period.

 

 

Start Date

The start date will be used to retrieve pumping well and head/concentration observation data for the model run.  When you define well data with absolute (calendar) dates, it is important that your start date reflects the actual start time for the model run. Absolute time well data must fall on or after that start date. Otherwise, these data will not be included in the simulation.

 

Also the start date cannot be changed once it has been set. If you inadvertently set the wrong start date, you can import your pumping well data and observation data in relative times (e.g. starting at 0), and you will see no difference in the numerical model inputs/outputs.

 

 

Setting the Start Date

Visual MODFLOW Flex uses a standard Windows date picker; a few tips are shown below on how to use this. By default, the current date will be set as the Start Date but you are encouraged to set this to an appropriate date for your model simulation.

 

Click on the button shown below, to load the Windows date picker.

 

 

 

 

The standard Windows calendar will appear.

Click on the month in the header (as shown below):

 

 

 

All months for the current year will appear as shown below.

Click on the year in the header:

 

 

 

A range of years will then appear as shown below.

Click on the range of years in the header:

 

 

 

A list of years for the previous decade will appear.

You can then use the  <  or > buttons to change the year.

Once you have reached the desired year (2000 for this example), select this on the calendar as shown below:

 

 

 

A list of months will then appear for that year.

Select January for this example, as shown below.

 

 

 

 

Finally, select "1" from the calendar as shown below:

 

 

 

The selected date will then appear for the Start Date.

 

 

Transport Objectives

 

An explanation of the Transport Objectives is available in the section Numerical Model - Define Objectives

 

Contaminant transport simulation can be enabled and setup in the conceptual model workflow. The species concentrations (for sinks/sources) can be defined while you define your conceptual boundary conditions.  However, the transport properties (initial concentrations, dispersion, etc.), are defined in the Numerical Model workflow, after you have defined a grid, and completed the "Convert to Numerical Model" step. This is explained in the section Define Properties (Numerical Model)

 

Click (Next Step) to proceed.

 


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