**Introduction to WinFlow**

*WinFlow* is a powerful yet easy-to-use groundwater flow model. WinFlow is similar to Geraghty & Miller's popular QuickFlow model which was developed by one of the authors of QuickFlow. The most notable improvement of WinFlow over *QuickFlow *is
its compatibility with Windows. WinFlow is a true Windows program incorporating a multiple document interface (MDI). See also - WinTran. It couples the steady-state groundwater flow model from WinFlow with a contaminant
transport model.

WinFlow is an interactive analytical model that simulates two-dimensional steady-state and transient groundwater flow. The steady-state module of WinFlow
simulates groundwater flow in a horizontal plane using analytical functions developed by Strack (1989). The transient module of WinFlow uses equations developed by Theis (1935) and by Hantush and Jacob (1955) for confined and
leaky aquifers, respectively. Each module uses the principle of superposition to evaluate the effects from multiple analytical functions (wells, etc.) in a uniform regional flow field.

WinFlow's steady-state module simulates the effects of the following analytic elements in two-dimensional flow: wells, uniform recharge, circular
recharge/discharge areas, and line sources or sinks. Any number of these elements may be added to the model including a uniform regional hydraulic gradient. WinFlow depicts the flow field using streamlines, particle traces, and
contours of hydraulic head. The streamlines are computed semi-analytically to illustrate groundwater flow directions. Particle-tracking techniques are implemented numerically to compute travel times and flow directions. Both
confined and unconfined aquifers are simulated with the steady-state module.

The transient module in WinFlow simulates the effects of wells, circular ponds, linesinks, and a uniform regional gradient for confined and leaky aquifers.
Numerical particle-tracking is also available in WinFlow's transient module. The transient module computes hydraulic heads using the Theis (1935) equation for confined aquifers and the Hantush and Jacob (1955) equation for
leaky aquifers.

WinFlow is simple to use and highly interactive, allowing you to create an analytical model in minutes. WinFlow features standard Windows pull-down menus and
dialogs to facilitate the model design. WinFlow is recomputed and recontoured either by selecting a menu item or by pressing a toolbar button. Streamlines and particle traces are added interactively and recomputed each time new
wells or other elements are added.

WinFlow can import a Drawing Interchange Format (DXF) file (from AutoCAD, for example) to use as a digitized base map. QuickFlow and ModelCad-format map files
may also be imported into WinFlow. The digitized map gives the modeler a frame of reference for designing the analytical model.

WinFlow produces report-quality graphics using any Windows device driver. Output may also be exported to a wide variety of file types including SURFER, Geosoft,
Spyglass, Windows Metafiles, and AutoCAD-compatible DXF files.

**WinFlow Features**

The features that WinFlow has in common with QuickFlow include the following:

- Simulates both steady-state and transient flow
- Simulates both unconfined and confined aquifers
- Simulates effects of wells, linesinks, ponds, and recharge
- Imports map files in DXF format, QuickFlow format, or ModelCad format
- Visualizes model results with water-level contour maps
- Illustrates groundwater flowpaths using streamlines and particle traces
- Simple data input
- Linesinks and ponds included in the Transient model
- Calibration targets and calculation of calibration statistics
- Each analytic element may have a title with full font selection
- Double-click an element to edit
- Click and drag to reposition elements, streamlines, or particles
- Click and drag to resize linesinks and ponds
- Multiple document interface (MDI) allows multiple models to be open at the same time
- Cut, copy, and paste elements to/from the clipboard
- Maps may be printed using any Windows device driver
- Coordinates and head are displayed as the cursor is moved
- Full context-sensitive help system (the entire manual is on-line)
- DXF file import from within WinFlow
- Common commands are available on the Toolbar
- Drag-and-drop input files into the WinFlow Window

**Applying WinFlow**

WinFlow is a powerful tool for analyzing two-dimensional groundwater flow problems. WinFlow can be applied to a wide variety of groundwater problems including
the following:

**WinFlow for Wellhead Protection:**
to delineate the capture zone around a groundwater supply well (travel times can be plotted on the capture zone or the capture zone can be computed for a given time, e.g., one year).

**WinFlow for Design of Remediation Systems:**
to evaluate a pump-and-treat cleanup system including selection of the number, location, and pumping rates of recovery wells. Injection wells and drains/trenches may also be evaluated.

**WinFlow for Regional Flow Modeling:**
Otto Strack originally designed the analytic element technique for application to regional flow problems. At a regional scale, vertical gradients are often negligible making a two-dimensional simulation a reasonable approximation. WinFlow includes calibration targets and calculation of statistics to aid in regional model calibration.

**WinFlow for Pumping Test Analysis and Design:**
the transient model in WinFlow offers a powerful way of selecting the optimal placement and monitoring schedule for observation wells. WinFlow can also be used to analyze test results by calibrating to the spatial distribution of drawdown at selected times (analogous to a distance-drawdown test). The calibration statistics mentioned above aid in evaluation of the test results.

A flexible user interface using pull-down menus and simple dialogs in WinFlow provides you with an easy method of setting up the model and rapidly getting to a
solution. The analytical model is developed in several steps as follows:

- Digitize a base map in a CAD package such as AutoCAD.
- Export the drawing to a DXF-format file.
- Double-click on the WinFlow icon to run WinFlow.
- Load the digitized map into WinFlow.
- Specify aquifer parameters.
- Choose a solution type (steady-state or transient).
- Add analytic elements to the model (wells, ponds, etc.).
- Calculate the model and contour the results.
- Add streamlines or particle traces to define flow paths.
- Create a graphical or summary output of the results.

These steps can be performed in WinFlow in a matter of minutes after the base map has been digitized. The base map is optional; however, it provides you with a
frame of reference in designing the analytical model.

WinFlow requires you to specify a few simple pieces of information or data to define the analytical model. Data can be classified in four different ways: (1)
fundamental data required by all problems; (2) data required for only transient applications; (3) data required for particle-tracking analysis; and (4) optional data.

Fundamental Data are required for all analytical models created by WinFlow. These data include:

- Regional gradient and direction of flow
- Hydraulic conductivity
- Aquifer top elevation and bottom elevation
- Reference head

Regional gradient and direction of flow are used to superimpose a uniform groundwater flow field on the analytical model. You must define the regional gradient
which has units of [L/L] (dimensionless) and the direction of flow. The direction of flow is entered in degrees with 0.0 degrees representing east, 90.0 degrees representing north, etc. You may enter a gradient of 0.0. You may
want to do this if you are computing drawdowns. Note that in unconfined aquifers, the gradient is defined at the reference point and may change throughout the model as the saturated thickness, and hence the transmissivity
changes.

Hydraulic conductivity is assumed to be homogeneous throughout the infinite aquifer and has units of [L/T], e.g., ft/d. The aquifer top and bottom elevations
have units of length [L], e.g., ft, and are used to compute transmissivity. In addition, the steady-state module in WinFlow allows for conversion to unconfined flow. Therefore, if the head falls below the top of the aquifer,
the model becomes unconfined.

The reference head defines a point where the head is known. In the steady-state model, the reference head is always constant and never changes during
simulations. The reference head may or may not be constant in the transient model, depending upon a user-selectable option. All computations are based upon the reference head which should be located as far from wells, ponds,
etc., as possible. The reference head is analogous to a constant head in a numerical model.

WinFlow assumes that you are using consistent units throughout the analysis. For example, if you are using length [L] units of feet and time [T] units of days,
hydraulic conductivity will be expressed in units of ft/d and pumping rates will be in units of ft^{3}/d (not gallons per minute).

__Transient flow__ problems require three additional data types in WinFlow including:

- Storage coefficient [dimensionless]
- Hantush leakage factor (denoted by L or B) [L]
- Time value to compute solution [T]

The Hantush Leakage factor denoted by the letter L or B has units of length (Hantush, 1956). The leakage factor is only required for leaky aquifers. It should
be set to zero for confined flow.

__Particle-tracking__ analyses in WinFlow require that porosity be defined. The porosity (dimensionless) is used to compute the average linear groundwater flow velocity at discrete points within the system.

__Optional Data__ types define the analytic elements of the model. These elements include the following information:

- Well locations and pumping rates
- Recharge rate
- Pond locations and recharge/discharge rates
- Linesink locations and recharge/discharge rates
- Calibration targets

All of the elements above are available for the steady-state model and all but recharge are simulated by the transient model.

__Wells __are defined by the coordinates of the center of the well, a pumping rate, and a well radius. The pumping rate has units of [L^{3}/T] such as ft^{3}/d.
A positive pumping rate indicates production and a negative rate indicates injection.

__Recharge__ is defined only for steady-state models and has units of [L/T] such as ft/d. The recharge is distributed over the entire infinite plane of the model. An ellipse defines the shape and position of the water-table mound created if there is no regional gradient. You must define the center coordinates of the ellipse, the length of the a-axis and b-axis of the ellipse, and the angle between the a-axis (long axis) of the ellipse and the x-axis of the model. The recharge rate should be a positive value.

__Ponds__ are circular recharge or discharge areas. Ponds are defined in a manner similar to wells. The coordinates of the center of the pond are given along with the radius of the pond. The pond infiltration rate has units of [L/T] and is computed by dividing the total discharge rate into or out of the pond by the area of the pond. Thus, the pond infiltration/discharge rate has the same units as recharge. A positive rate indicates infiltration and negative indicates discharge from the aquifer.

__Linesinks__ are linear recharge or discharge features. The linesink is defined by providing the coordinates of each end point and either an infiltration/discharge rate or a head. If the linesink is defined in terms of head, the model will compute a discharge rate based on the given head value (assumed to be at the center of the linesink). Linesink discharge/infiltration rates have units of [L^{2}/T]
which is computed by dividing the total discharge rate by the length of the line. Thus, the linesink rate (or strength) is a rate per unit length. The sign convention for linesinks is the same as wells; positive indicates
pumping or production and negative signifies injection or infiltration.

After defining all aquifer properties and analytic elements, you run WinFlow by selecting Calc from the main menu and Recalculate from the pull-down menu.
WinFlow will the compute the hydraulic head on a regular grid of points and contour the results. To illustrate groundwater flow directions and travel times in WinFlow, you may add any number of particle traces. Reverse particle
tracking is used to compute capture zones and forward tracking to create a flow net.

WinFlow Tutorial

See also - WinTran. It couples the steady-state groundwater flow model from WinFlow with a contaminant transport model.