Single-event Wind Erosion

Evaluation Program

SWEEP

User Manual

DRAFT

February, 2008

USDA-ARS

Wind Erosion Research Unit

Manhattan, Kansas, USA

Table Of Contents

Page

Introduction	1

Installation	1

SWEEP Science	2

Introduction	2

Soil Surface Conditions	2

Erosion Processes Simulated	3

Outputs	5

Interface Reference	7

Menu Bar	8

File	8

Run	8

View	9

Help	11

Tabs	12

Field Tab	13

Biomass Tab	14

Soil Layers Tab	16

Soil Surface Tab	18

Weather Tab	20

Making a SWEEP Run	25

Viewing Outputs	25

Soil Erosion Viewer	26

References	28

Appendix	29

Loading SSURGO Data	29

Downloading SSURGO Soil Data	30

Residue Cover Estimation	33

Random Roughness Estimation	37

SWEEP Command Line Options	43

Introduction

The Single-event Wind Erosion Evaluation Program (SWEEP) is a process-based computer model that simulates wind erosion for a single-day storm event. The model consists of the EROSION submodel of the Wind Erosion Prediction System (WEPS) model coupled with a simple graphical user interface.

Installation

SWEEP can be downloaded at: www.weru.ksu.edu/weps

This is the WEPS model web page from which one can download a number of WERU products. The process to download the SWEEP model only is described next.

Click 'Downloads' at the top of the screen. This will take you to WEPS Download Registration screen. After entering registration information you will proceed to the Downloads Page for WEPS. Click the latest WEPS version to download the installation program. The download file consists of an executable file that will allow the user to install WEPS and SWEEP products onto your Windows computer. When you install and get to the 'Setup Type" screen, choose the 'Custom Installation' option and be sure to at least choose the options (i.e., remove the red X) for the 'SWEEP'. Follow the prompts to install SWEEP on your computer. Of course you are free to install any other options you wish. This process will put an icon on your computer desktop for the options you chose as well as make them accessible through "Start" > "Programs" > "USDA Applications".

Contact WERU if you need assistance at:

Phone:	785-537-5542

E-mail:	weps@weru.ksu.edu

SWEEP Science

Introduction

This section briefly describes the science behind the Single-event Wind Erosion Evaluation Program (SWEEP). The science portion of SWEEP, is the EROSION submodel of the Wind Erosion Prediction System (WEPS). For an in-depth description of the equations used in this model, see the WEPS Erosion Submodel Technical Description (Hagen, 1995).

The objective of the SWEEP model is to simulate the components of soil loss/deposition over a rectangular field in response to wind speed, wind direction, field orientation, and surface conditions, on a sub-hourly basis (Fig. 1). In SWEEP, barriers may be placed on any or all field boundaries as well as within the field. When barriers are present, the wind speed is reduced in the sheltered area on both the upwind and downwind sides of the barriers. The model determines the threshold friction velocity at which erosion can begin for each surface condition. When wind speeds exceed the threshold, the model calculates the loss/deposition over a series of individual grid cells representing the field. The soil/loss deposition is divided into components of saltation/creep and suspension, because each has different transport modes, as well as off-site impacts. Finally, the field surface is periodically updated to simulate the changes caused by erosion.

Parameters Describing Soil Surface Conditions

Surface roughness is represented by both random roughness and oriented roughness. The parameters used are standard deviation of the surface heights for random roughness and the height, width of ridge tops, and spacing of ridges for oriented roughness.

Surface cover is represented at three levels (Fig. 2). At the first level, surface rock, aggregates and crust compose 100 percent of the cover. At the second level, the parameter is the fraction of the crusted surface covered with loose, erodible soil. When there is no crust, this parameter is zero. At the third level, the parameter is the fraction of total surface covered by flat, random biomass.

The aggregate density and size distribution are soil parameters that determine soil mobility. The dry mechanical stabilities of the clods and crust are input parameters that indicate their resistance to abrasion from impacts by eroding soil. Surface soil wetness is also input and used to increase the threshold friction velocity at which erosion begins.

Uniformly distributed standing biomass is 5 to 10 times more effective in controlling wind erosion than is flat biomass, and thus, standing biomass is treated separately. The wind friction velocity above standing biomass is depleted by the leaves and stems to obtain the friction velocity at the surface that is used to drive erosion (Fig. 3). Leaves are represented by a leaf area index and stems are represented by a stem silhouette area index.

Erosion Processes Simulated

Soil transport during wind erosion occurs in three modes: creep-size aggregates, 0.84 to 2.0 mm (0.033 - 0.079 in.) in diameter, roll along the surface; saltation-size aggregates, 0.10 to 0.84 mm (0.004 - 0.033 in.) in diameter, hop over the surface; and suspension-size aggregates, less than 0.01 mm (0.004 in.) in diameter, move above the surface in the turbulent flow. Variations in friction velocity, aggregate density, and sediment load obviously may change the mass of aggregates moving in a given mode. Saltation and creep are simulated together because they have a limited transport capacity that depends mainly upon friction velocity and surface roughness. The suspension component is simulated with no upper limit on its transport capacity at the field scale. A portion of the suspension component is simulated as PM-10 (i.e., particulate matter less than 10 micrometers (0.0004 in.) in diameter), which is regulated as a health hazard.

Multiple physical erosion processes are simulated in the SWEEP model, and these are illustrated for a single grid cell in Fig. 4. The two sources of eroding soil are emission of loose soil and entrainment of soil abraded from clods and crust. These sources are apportioned between saltation/creep and suspension components on the basis of the source process and soil characteristics. Particulate matter less than 10 microns (PM10) is considered a component of suspension. Three processes deplete the amount of moving saltation/creep. These include trapping in surface depressions, interception by plant stems/leaves, and breakage of saltation/creep size particles and aggregates into suspension-size.

Simulation of surface rearrangement is accomplished by allowing emissions to deplete the loose soil and armor the surface in the upwind field area. In contrast, processes such as abrasion of the protruding aggregates and trapping in depressions dominate in downwind areas and lead to smoothing the surface and a build-up of loose saltation/creep. A build-up of saltation/creep often occurs, because the transport capacity may be satisfied, but abrasion of clods/crust continues to create additional saltation/creep-size soil.

Typical behavior of the downwind soil discharge simulated along a line transect for the saltation/creep and suspension components is illustrated in Fig. 5. The suspension component keeps increasing with downwind distance, even though saltation/creep reaches transport capacity. This is because the sources for suspension-size soil are usually active over the entire field. These sources include emissions from impacts on loose soil, abrasion from clods/crust, and breakage from impacting saltation/creep-size aggregates. Moreover, the suspension component has a transport capacity many times larger than that of saltation/creep, so on large fields it is the 'freightliner' for moving soil whereas saltation/creep is merely the 'pickup truck'. The vertical extent of the suspension component at transport capacity is on the order of a few kilometers while the vertical limit of saltation/creep is on the order of approximately one meter.

Outputs

The SWEEP model calculates total, suspension, and PM-10 soil loss/deposition at each grid cell in the field. The grid cell data are summarized reported to users as averages over the field for selected periods. The model also calculates the components of soil discharge crossing each field boundary. These are reported to users, according to the size ranges of aggregates as saltation/creep, suspension, and PM-10. These latter outputs are useful for evaluating off-
site impacts in any given direction from the eroding field.

Interface Reference

The installation process described previously, should put the SWEEP icon on your desktop, if you chose that option. The program is also accessible through "Start > All Programs > USDA Applications > WEPS 1.0 > SWEEP". Click the desktop icon or access the program through the "Start" menu to begin the SWEEP interface. The SWEEP interface (Fig. 6) should appear at startup and consists of menu and tool bars and five input screens arranged in tabs across the top of the screen. Output options include text output files as well as 3D graphical output capabilities for the entire day as well as subdaily (e.g., hourly) plots.

Menu Bar

The menu bar is at the top of the SWEEP screen to allow easy access to the main functions of the model. Each item on the menu bar is described next.

File

The 'File' menu is a drop down list of various computer operations pertaining to SWEEP files. The File menu contains the following options:

New - Allows user to create a new input file from scratch (Ctrl-N).

Open - Allows user to open an existing input file (Ctrl-O).

Save - Saves the currently displayed input file to its current file name (Ctrl-S).

Save As - Saves the currently displayed input file under a different file name (Ctrl-A).

Load Soil File - Opens a file chooser to select a WEPS generated soil file (*.ifc) which is then used to populate the soil tabs.

Load SSURGO File - Opens a list of soils previously obtained from the NRCS Soil Survey Geographic (SSURGO) database. This opens a window titled 'Select SSURGO Soil'. Navigate through the database tree to find the soil survey area (or county) desired then select a soil. A full description of how to navigate to select a soil as well as how to download soil data from the SSURGO database and convert them to the correct file format is available in the Appendix of the SWEEP User Guide.

Exit - Exit the SWEEP program (Alt-F4).

Run

This menu allows the user to run SWEEP using the current inputs specified on the SWEEP screen. Before running a SWEEP simulation, the user should save the input file first. The 'Run' menu on the SWEEP screen displays the following options:

'Run' - Begin a SWEEP simulation using the current selected inputs (Ctrl-R).

'Find Threshold' - Opens a window that allows the user to select a wind station for which to calculate wind speed threshold at which erosion will occur as well as other wind parameters by direction and month (Ctrl-H). Once a stations is selected, clicking the 'Run' button on the window generates a table that displays the following information by month and direction. Generation of the Threshold Table may take several minutes to complete. See Figure 7.

•	Threshold (m/s) - Wind speed from the specified direction at which erosion begins based on the given surface conditions (soil and biomass).

•	Winds > Threshold (%) - Percent of winds coming from the specified direction for this month that exceeds the threshold wind speed for that direction.

•	Dir Prob (%) - Probability of wind coming from the specified direction for the month.

•	Thresh Prob (%) - Probability of any wind exceeding the threshold wind speed from any direction for the month.

View

This menu allows the user to view input or output for the most recent (i.e., most current) SWEEP run. The View menu on the SWEEP screen displays the following options:

'Input Text' - Displays the current SWEEP input file.

'Output Text' - Displays the most recent output file (Ctrl - Shift - T).

'Graph Total' - Displays the Sweep Soil Erosion Viewer that allows the user to view 3-D plots of various SWEEP outputs for the day (Ctrl - Shift - G ).

'Graph Subdaily' - Displays the Sweep Soil Erosion Viewer that allows the user to view 3-D plots of various SWEEP outputs for each time period (e.g., hour) of the day (Ctrl - Shift - D).

'Threshold Run' - Displays the result of the 'Find Threshold' obtained under the 'Run' menu. To open a previously created Threshold Run table, one must open an input file for the previously created run.

'Load Old Run' - Loads a previous run to the SWEEP window.

Tools

This menu contains miscellaneous tool options for SWEEP, including:

'Configure' - Displays a tabbed window with the following various configuration options for SWEEP (Ctrl - Shift -C).

•	'Files' - Tab that allows the user to select executable files and command-line arguments (see Appendix of the WEPS User Manual for the command-line argument definitions):

SWEEP exe - Enter the path and file name for the default SWEEP executable or click the folder icon to display a file chooser.

SWEEP cmd - Enter the default SWEEP command-line arguments (see Appendix for argument list).

Soil DB - Enter the default directory (which includes subdirectories) for soil database files. These files can be WEPS 'ifc' files or soil SSURGO Access database files (click the path or click the folder icon to display a file chooser). If the file SDMDataAccess.nrcs.usda.gov.db is in the specified directory, the user also has the option of selecting soil data directly from NRCS Soil Data Mart (internet access required).

Soil DB spec - Enter the JDBC:OBDC driver specification for accessing SSURGO soil data in a Microsoft Access database file. This field should be left blank if the "Soil DB" field specifies a directory containing "ifc" soil files.

Work Directory - Enter the path and file name for the default SWEEP working directory or click the folder icon to display a file chooser.

Wind DB file - Enter the path and file name for the default wind database file or click the folder icon to display a file chooser.

Wind Index File - Enter the path and file name for the default wind database index file or click the folder icon to display a file chooser.

•	'Run' - Tab for run options:

Inputs - Enter the number of simulation grid points in the x and y directions as well as the number for surface updating interval. This interval is the time between surface update calculations in seconds. If the "Turn off surface updating" box is checked, the surface conditions will not be updated as a result of erosion. Note that the default number of grid points in each direction is 30 for a field without barriers and 60 for a field with barriers. Significantly increasing the number of grid cells may result in model instability.

Outputs - Click the check box to enable outputs for the listed items.

•	'Email' - Tab for email settings:

Sender Addr - Enter the default email address of the sender.

SMTP Server - Enter your mailhost SMTP server address.

Comments - Default recipient for comments to WEPS developers.

Bugs - Default recipient for a bug report.

'Email' - Displays a window allowing the user to send email comments to WERU, providing the computer is connected to the Internet and the email configuration options are properly configured. The user can also attach current SWEEP run files to the messages (Ctrl - Shift - E).

Help

This menu contains help options for SWEEP, including:

'About' - Displays the Build Date, Release Number, and Java Runtime Version used for SWEEP.

'Help' - Displays a window containing the SWEEP online help system (F1).

'User Guide' - Opens a copy of the SWEEP User Guide in PDF format (must have capability to read PDF files).

Button Bar

At the top of the SWEEP window (below the menu bar) is a series of buttons with icons, designed to help the user in the operation of SWEEP.

This button allows user to create a new SWEEP run from scratch. This has the same function as selecting 'New' under 'File' on the menu bar.

This button opens an existing SWEEP run. This has the same function as selecting 'Open' under 'File' on the menu bar.

This button saves the currently displayed SWEEP run to its current file name. This has the same function as selecting 'Save' under 'File' on the menu bar.

This 'Run' button begins a SWEEP simulation run.

This button displays graph of the grid soil loss for the day along with other outputs for the current run (see Figure 10). A run must have been completed before the graph is displayed.

This graph displays the graph window of the grid soil loss for sub-periods for the day (e.g., hourly) for the current run (see Figure 11). A run must have been completed before the graph is displayed.

Tabs

Each input item is arranged into tabs just below the menu bar. Click on the tab to access input page. Contents of each tab is described next. A range of absolute values, which are valid for SWEEP, are given for each parameter where applicable. Values out of range have not been extensively tested and effects on model outputs are unknown. Values that are outside Methods for estimating some parameters from other known properties are also given.

Field Tab

The Field tab (Fig. 6) describes the field dimensions and orientation. It also describes barrier placement and properties. A Field View panel (Fig. 8) is located to the upper right of the SWEEP Field tab. This panel is for viewing only and is not editable. It is designed to give the user a view of the field size, shape, and orientation (green). The placement of any barriers present is also displayed (red). The field tab parameters are defined next.

X-Length -	The length of the simulation region in the X-direction, meters.

Absolute range: 10.0 to 1600.0

Y-Length -	The length of the simulation region in the Y-direction, meters.

Absolute range: 10.0 to 1600.0

Angle -	Orientation of the simulation region in degrees, clockwise from North (i.e., North = 0.0, East = 90.0, etc.).

Absolute range: 0.0 to 360.0

Add New Barrier -	Allows the user to add a barrier to the field and provide a reference name for that barrier.

Absolute range: 0 to 500

Remove Selected -	Allows the user to remove the selected barrier from the field.

Barrier Table

The barrier table is at the bottom of the field tab and allows easy addition of barriers and editing of their properties. Clicking on a barrier in the Field View panel highlights the properties for that barrier in the Barrier Table below. Note that although up to five hundred barriers may be simulated, large numbers (>5) of barriers and barriers within the field borders have not been extensively tested. Barriers at an angle to the field borders are also allowed but are similarly not extensively tested.

Barrier -	Displays the reference name for the barrier specified by the user when clicking the "Add Barrier" button.

Type-	Select from a list of previously defined barrier types by clicking the down arrow to the right of the cell. Upon selection of a barrier, the properties will be entered. The properties may be edited in which case the type name will be changed to <custom>. One may also choose <custom> to specify barrier properties from scratch.

X1, Y1 -	The X,Y coordinate of the first linear barrier end point, meters.

Absolute range: 0.0 to ?

X2, Y2 -	The X,Y coordinate of the second linear barrier end point, meters.

Absolute range: 0.0 to ?

Height -	The average height of the barrier, meters.

Absolute range: 0.0 to ?

Width -	The average width of the barrier, meters.

Absolute range: 0.0 to ?

Porosity -	The Average barrier optical porosity (1.0 - silhouette area), m2/m2.

Absolute range: 0.0 to 1.0 (i.e., 1.0 = solid barrier)

Biomass Tab

The Biomass tab describes the crop and biomass conditions on the soil surface.

Residue average height -	The average height of standing residue, meters.

Absolute range: 0.0 to 3.0

Residue stem area index -	The residue stem area index, m2/m2. This represents the area of the stems only (no leaves) per square meter as viewed parallel to the soil surface. The user may also click the "Estimate" button to the right of the input field to open an input window to estimate residue stem area index based on average temperature for the day (o C) and elevation (meters). The value in this field may also be edited if desired.

Absolute range: 0.0 to 3.0

Estimated by: RSAI = stem diameter (m) * stem height (m) * stem population (#/m2)

Residue leaf area index -	The residue leaf area index, m2/m2.

Absolute range: 0.0 to 3.0

Residue flat cover -	The flat biomass cover, m2/m2. The user may also click the button to the right of the input field to display photo examples (see Appendix) of residue cover for wheat straw. Placing the cursor over the photo displays the amount of residue below the photo. Clicking on a photo closes the window and enters the cover value into the filed. The value in this field may be edited if desired.

Absolute range: 0.0 to 1.0

Growing crop average height -

The average height of the growing crop, meters.

Absolute range: 0.0 to 3.0

Growing crop stem area index -

The growing crop stem area index, m2/m2. This represents the area of the stems only (no leaves) per square meter as viewed parallel to the soil surface. The user may also click the "Estimate" button to the right of the input field to open an input window to estimate growing vegetation stem area index based on average temperature for the day (o C) and elevation (meters). The value in this field may also be edited if desired.

Absolute range: 0.0 to 3.0

Estimated by: CSAI = stem diameter (m) * stem height (m) * stem population (#/m2)

Growing crop leaf area index -

The growing crop leaf area index, m2/m2.

Absolute range: 0.0 to 12.0

Row spacing -	The row spacing cover, meters. Use a value of 0.0 if not planted in rows (e.g., broadcast seeded).

Absolute range: 0.0 to ?

Seed placement -	Specify location of seed as either on the ridge top or in the bottom of the furrow. The value doesn't matter if no ridges exist or if broadcast seeded.

Soil Layers Tab

The Soil Layers tab describes the soil properties in each layer of the soil. Note that the current version of SWEEP only accounts for the surface layer properties when simulating erosion. Simulating erosion for lower layers is described at the end of the Soil Layers tab discussion.

Number of layers -	The number of soil horizons or layers for which properties are reported. NOTE: Only the top layer (layer 1) is used in the current version of SWEEP.

Absolute range: 1 to 3

Thickness -	The thickness of each soil layer, millimeters.

Absolute range: 0.0 to ?

Bulk density -	The oven dry weight of the less than 2 mm soil material per unit volume of dry soil, Mg/m3.

Absolute range: 0.001 to 1.8

Sand fraction -	Mineral particles 0.05 to 2.0 mm in equivalent diameter as a weight fraction of the less than 2.0 mm fraction, kg/kg.

Absolute range: >0.0 to 1.0

Estimated by: sand = 1.0 - (silt + clay)

Very fine sand fraction -	Mineral particles 0.05 to 0.1 mm in equivalent diameter as a weight fraction of the less than 2 mm fraction, kg/kg.

Absolute range: 0.0 to 1.0

Silt fraction -	Mineral particles 0.002 to 0.05 mm in equivalent diameter as a weight fraction of the less than 2.0 mm fraction, kg/kg.

Absolute range: >0.0 to 1.0

Estimated by: silt = 1.0 - (sand + clay)

Clay fraction -	Mineral particles less than 0.002 mm in equivalent diameter as a weight fraction of the less than 2.0 mm fraction, kg/kg.

Absolute range: >0.0 to 1.0

Estimated by: clay = 1.0 - (silt + sand)

Rock volume fraction -	The volume fraction of the layer occupied by the 2.0 mm or larger (20 mm or larger for wood fragments) on a whole soil basis, m3 /m3.

Absolute range: 0.0 to 1.0

Avg aggregate density -	The oven dry weight of the less than 2 mm soil aggregates per unit volume of dry soil aggregates, Mg/m3.

Absolute range: 0.6 to 2.5

Estimated by:

ag den = 2.01 *(0.72 + 0.00092 * layer depth) for layer depth =< 300 mm

ag den = 2.0

for layer depth > 300 mm

Avg dry aggregate stability -	Mean of natural log of aggregate crushing energies, ln(J/kg).

Absolute range: 0.1 to 7.0

Estimated by:

ag stab = 0.83 + 15.7 * clay - 23.8 * clay 2

GMD of aggregate sizes -	Soil aggregate geometric mean diameter of the modified log-
normal distribution, mm.

Absolute range: 0.03 to 30.0

Estimated by:

ag gmd = exp(l.343 - 2.235 * sand - 1.226 * silt - 0.0238*sand/clay + 33.6 * om + 6.85*CaCO3)*(1.0 +0.006*layer depth)

GSD of aggregate sizes -	Soil aggregate geometric standard deviation of the modified log-normal distribution, dimensionless.

Absolute range: 1.0 to 20.0

Estimated by:

ag gsd = 1.0 / (0.0203 + 0.00193(aggr. gmd) + 0.074 / (aggr.gmd) 0.5)

Minimum aggregate size -	Lower limit of the modified log-normal aggregate size distribution, mm.

Absolute range: 0.001 to 5.0

Estimated by: ag min = 0.01

Maximum aggregate size -	Upper limit of the modified log-normal aggregate size distribution, mm.

Absolute range: 1.0 to 1000.0

Estimated by:

ag max = (ag gsd) p * (ag gmd) + 0.84

where p = 1.52 * (ag gmd)-0.449

Soil wilting point water content -

The amount of soil water retained at 15 bars (1500 kPa), expressed as a percentage of the less than 2 mm, oven-dry soil by volume, Mg/Mg.

Absolute range = 0.0 to ??

Estimated by: Saxton, et al. (1986)

Soil wilting point water content -

The amount of soil water retained at 15 bars (1500 kPa), expressed as a percentage of the less than 2 mm, oven-dry soil by volume, Mg/Mg.

Absolute range = 0.0 to ??

Estimated by: Saxton, et al. (1986)

At the bottom of the 'Soil Layers' tab are two arrow boxes. The left arrow can be used to cycle the lower layers to the surface. This may be useful in simulating fields that have had their surfaces removed, such as for construction. The right arrow cycles the layers down creating a "blank" layer at the surface. This may be useful in simulating an amendment to the original surface. Note! This function cannot be reversed and the user may have to reload the soil if the layers are cycled past the desired layer. The user is therefore advised to save the soil file before performing any cycling of layers to avoid loss of soil data.

Soil Surface Tab

The Soil Surface tab describes the physical properties of the soil surface.

Surface crust fraction -	Fraction of surface covered with consolidated soil, as opposed to aggregated soil, m2/m2.

Absolute range = 0.0 to 1.0

Surface crust thickness -	Average thickness of the consolidated zone in the surface layer, mm.

Absolute Range: 0.0 to 23.0

Loose material on crust -	Fraction of total crusted surface area covered with loose material on the crust, m2/m2.

Absolute range = 0.0 to 1.0

Loose mass on crust -	Mass of the loose, saltation-size soil on top of the surface crusted area, kg/m2.

Absolute range = 0.0 to 3.0

Estimated by: 0.0

Crust density -	The density of the soil crust, Mg/m3.

Absolute range = 0.6 to 2.0

Estimated by: aggregate density

Crust stability -	Mean of natural log of crust crushing energies, ln(J/kg).

Absolute range = 0.1 to 7.0

Estimated by: aggregate stability

Allmaras random roughness -	The standard deviation of elevation from a plane of a random soil surface, including any flat biomass adjusted as suggested by Allmaras et al. (1966), mm. The user may also click the button to the right of the input field to display photo examples (see Appendix) of random roughness. Placing the cursor over the photo displays the roughness below the photo. Clicking on a photo closes the window and enters the roughness value into the filed. The value in this field may be edited if desired.

Absolute range = 1.0 to 70.0

Ridge height -	The height of soil ridges from bottom of furrow to top of ridge, mm. NOTE: If no ridges, then specify 0.0.

Absolute range = 0.0 to 500.0

Estimated by: 0.0

Ridge spacing -	Spacing between ridge tops, mm. NOTE: If no ridges, then specify 0.0, if ridge height > 0.0 then a spacing must be specified.

Absolute range = 10.0 to 2000.0.

Estimated by: 10.0

Ridge width -	Width of the top of the ridge (i.e. bed width), mm. NOTE: If no ridges, then specify 0.0.

Absolute range = 10.0 to 4000.0

Estimated by: 10.0

Ridge orientation -	Direction parallel to the tillage ridge, clockwise from true North, degrees.

(i.e., North/South = 0.0 or 180, East/West = 90.0)

Absolute range = 0.0 to 180.0

Estimated by: 0.0

Dike spacing -	Spacing between dikes in the furrow, mm. NOTE: If no dikes, then specify 0.0.

Typical Range: 0.0 to 1000.0

Snow depth -	Average depth of snow on the soil surface, mm.

Typical Range: 0.0 to 1000.0

Hourly surface water content -

The near surface water content for each hour of the day, Mg/Mg.

Absolute Range: 0.0 to 0.50

Weather Tab

The Weather tab describes the weather parameters for the simulation location (Figure 9). Parameters on this Tab include:

Air density -	The average density of the air at the simulation location for the day, kg/m3. The user may also click the "Estimate" button to the right of the input field to open an input window to estimate air density based on average temperature for the day (o C) and elevation (meters). The value in this field may also be edited if desired.

Absolute Range: 0.7 to 1.5

Wind direction -	Wind direction (degrees) for the 1 to 3 periods of the day with the fastest wind speeds, measured clockwise from North.

Typical Range: 0.0 to 359.9

Anemometer height -	The height of the anemometer above the soil surface at which the wind speeds were measured, m

Absolute range: 0.5 to 30.0

Aerodynamic roughness at anemometer site -

Aerodynamic roughness at the site where wind speeds were measured, mm

Absolute Range: 0.5 to 2000.0

Zo location flag -	Select the location where the wind data was measured: either measured at a weather station that was remote from the simulation site or measured at the field simulation site. If wind speeds were measured at a remote location - Zo is specified under the 'Aerodynamic roughness at anemometer site'. If wind speeds were measured on the simulation field location - Zo varies based on field surface and is calculated within sweep ('Aerodynamic roughness at anemometer site' is ignored).

Clicking this button displays a window with fields to enter the Weibull wind speed distribution parameters below for the location to be used to simulate wind speeds. Once the parameters are entered and the user clicks 'Calculate and return', SWEEP calculates wind speeds for the day based on the parameters. If the Weibull parameters are unknown or the user has measured wind data, the button should not be clicked, and wind speeds should be entered into the table at the bottom of the Weather Tab.

Fraction of time winds are calm -

The fraction of time intervals that are calm for the day, hr/hr. NOTE: This is only available when "Weibull" is selected.

Absolute range: 0.0 to 1.0

Weibull "c" factor -	The scale parameter "c" for the Weibull distribution describing the wind speed distribution for the site, m/s. NOTE: This is only available when "Weibull" is selected.

Absolute range: 0.0 to 30.0

Weibull "k" factor -	The shape parameter "k" for the Weibull distribution describing the wind speed distribution for the site, unitless. NOTE: This is only available when "Weibull" is selected.

Absolute range: 1.0 to 3.0

Number of intervals/day to run EROSION -

The number of time steps erosion is calculated for each day. The is equal to the number of wind speeds input for the day. Note:

no. time step = 24 means hourly updates

no. time step = 48 means 30 minute updating

no. time step = 96 means 15 minute updating

Absolute range: 24 to 96

Wind table -	Wind speeds for each time interval of the entire day in meters/second. Wind data are typically averages for the period. More frequent than hourly estimates of wind speed will likely improve accuracy of estimated erosion. Likewise the maximum "instantaneous" wind speed for each time period is better than an hourly average.

Absolute range: 0.0 to ??

Notes: The number of wind speeds must equal the "Number of interval/day to run EROSION" parameter entered previously. If wind speeds are only available for every 3 hours (common with older data sets) then repeat the wind speed for the adjacent two hours with missing data. Similarly, if wind speeds are only available for daylight hours, values must be entered for the night time periods. The data can be cut and pasted from a text file or spread sheet provided that each wind speed is delimited by a tab or white space.

Making a SWEEP Run

All available input parameters must have a value for SWEEP to successfully run. The user has three options for populating the input parameters on the tabs. One may, 1) open a previously saved run, which may be run as is or parameters may be modified and then run, 2) load a soil file which populates soil dependent parameters allowing the user to populate remaining parameters, 3) populate all parameters from scratch. The user must save newly created run parameters under a file name through the File menu prior to a run. If the user tries to make a run without saving parameters to a file, a prompt will appear asking the user to save the data to a file. Note that known characters that are invalid in SWEEP file names include: \ / < > | ? * & " ~ ` '

When available input parameters have been populated within each tab and the file saved, selecting 'Run' from the Run menu begins a SWEEP simulation. You may briefly see a run dialog window appear on the screen during the simulation run. A run typically takes less than a few seconds.

Viewing Outputs

After the run completes, the user may click the "View" menu to select options to view the text input file parameters, view the text output file, and open the Soil Erosion Viewer, a simple 3-D graphical program to view graphs of the total grid data or view the subdaily graphical data. One may also view the previously generated threshold run table. The output file is placed by default in the same directory as the input file and has the same name as the input file name with a '.egrd' extension.

The output file is the raw output from the model and has in-line documentation describing each section of output. The output file provides the following information. First, it echoes the input values. It then provides erosion loss (kg/m of border width) passing each border of the field in terms of total, creep+saltation, suspension, and PM10. Next, it provides the amount of soil leaving each field grid cell in terms of total, creep+saltation, suspension, and PM10. Negative values are a net loss and positive values are a net gain (i.e., deposition). Finally it gives averages for field and boundary losses for total, creep+saltation, suspension, and PM10.

Soil Erosion Viewer

The SWEEP Soil Erosion Viewer is a simple graphical viewer that provides 3-D plots of field erosion loss and a table of field grid data being plotted. The Soil Erosion Viewer is accessed using the "Graph" menu items under the SWEEP "View" menu bar option or clicking the 'Graph Total' button on the tool bar. Right clicking within the graph area displays formatting and other customizing options for the viewer.

Daily Total Output

Figure 10 shows the graph window for soil loss for the day. A menu at the top of the Soil Erosion Viewer screen provides the following graphing functions.

The drop down list near the top of the screen allows the user to select various SWEEP output parameters to plot and include total, saltation/creep, suspension, or PM10 soil loss by grid cell for the day.

To the right of the drop down list are two buttons that allow the user to rotate the graphical view to the right or to the left.

Below the graphical output is a table depicting the selected output for each grid cell followed by a listing to loss totals for the entire field.

At the bottom of the window are summary information for field and boundary loss.

Subdaily Output

Figure 11 shows the graph window of the grid soil loss for sub-periods for the day (e.g., hourly). The number of intervals per day for which erosion is calculated is set under the "Weather" Tab. By changing the number of intervals, the user can select the time interval between erosion calculations (e.g., 24 = hourly or 48 = ½ hour intervals).

The drop down list on the left of the top of the screen allows the user to select various SWEEP output parameters to plot.

The drop down list at the center top of the screen allows the user to select the time period os the day to plot. Clicking the right or left arrow keys allows the user to step forward or back through the time periods of grid loss output. The appropriate plot and grid data are displayed below for the selected time interval.

To the right of the drop down lists are two buttons that allow the user to rotate the graphical view to the right or to the left.

Below the graphical output is a table depicting the selected output for each grid cell followed by a listing to loss totals for the entire field.

References

Allmaras R.R., R.E. Burwell, W.E. Larson, and R.F. Holt. 1966. Total porosity and random roughness of the interrow zone as influenced by tillage. USDA Conservation Research Report 1966, Vol. 7, p. 1-22.

Hagen, L.J. 1995. Wind Erosion Prediction System (WEPS) Technical Description: Erosion submodel. Proceedings of the WEPP/WEPS Symposium. Soil and Water Conservation Society, Ankeny, IA.

Saxton, K. E., W.J. Rawls, J.S. Romberger, and R. I. Papendick. 1986. Estimating generalized soil-water characteristics from texture. Soil Sci. Soc. Amer. J. 50(4):1031-1036.

Appendix

Loading SSURGO Data

Soil data for a SWEEP simulation run may be obtained from the Natural Resources Conservation Service - Soil Survey Geographic (SSURGO) database file. Accessing this database will allow the population of many of the soil parameters on the SWEEP screen. Clicking on the SWEEP 'File' menu and then clicking 'Load SSURGO File', opens a window titled 'Select SSURGO Soil' (Fig. 12). Navigate through the database tree to find the soil survey area (or county) desired. Navigation is performed by clicking on the 'key' symbol to open the display to the next level of the tree. To close a level of the tree, click the 'key' symbol to close the level of the tree. The soil files are listed according to the soil map unit symbol, map unit name, surface texture, and local phase. Selecting a soil then displays its components and the percentage that each component contributes to the map unit. The user can choose to select the dominant soil for the field or select the most erodible soil of the field. Click on a soil component to highlight it and click the 'Select' button at the top of the screen (or double click the component with the left mouse button). This action returns the user to the main SWEEP screen and converts the soil from the SSURGO database to a WEPS soil file format. SWEEP then loads the data into many of the Soil Layer and Soil Surface tabs. Clicking the 'Cancel' button in the 'Select SSURGO Soil' window aborts the selection of a new soil. The 'Question' button opens the general help system for SWEEP.

Downloading SSURGO Soil Data

This section describes how to download soil data from the NRCS Soil Data Mart and how to extract it for use within WEPS and SWEEP. A Microsoft Access database is available for importing the data in the export file. You must have Microsoft Access 97 or later installed on your PC.

Soil data for NRCS and most other users in the US, is currently available for download from the NRCS Soil Data Mart at: http://soildatamart.nrcs.usda.gov/ . Soil survey data that is exported from the Soil Data Mart is in what is referred to as "SSURGO" (Soil Survey Geographic) format. To obtain soil data for a Soil Survey Area of interest, go to the Soil Data Mart and click 'Select State' at the top of the Soil Data Mart screen. Select the desired state then click 'Select Survey Area' or 'Select County'. Select the soil survey area, then click 'Download Data'. On the download screen select 'Tabular Data Only', select the version of Microsoft Access on your computer, and enter your e-mail address, then click 'Submit Request'. You will see a message stating "Your request has been logged. At a later time you will receive an e-mail with a link to download the export file. The format of an export file name is: soil_ssasymbol.zip, where 'ssasymbol' is the soil survey symbol of the corresponding soil survey area.

After the export file has been copied to your PC, it must be unzipped by using either WinZip or a similar program. For additional information, please see the file named README.txt in the root directory that is created by unzipping the export file. For additional soil survey areas, each zip file should be copied and unzipped into individual directories. When an export file is unzipped, the following directory hierarchy is produced in the directory to which the export file was unzipped:

\spatial

\tabular

The top-level directory contains the following files:

soil_metadata_ssasymbol.txt - a Federal Geographic Data Committee (FGDC) metadata file in plain ASCII format.

soil_metadata_ssasymbol.xml - the same FGDC metadata file in XML format.

readme.txt - a text file containing additional information.

The root directory will also contain a zipped, empty MS Access SSURGO template database, if one was requested as part of the download. The non-extension part of the zipped template database file name varies, but if one was included, it will be the only file in the top-level directory with an extension of "zip". This file should be unzipped as well.

The directory "tabular" contains any tabular data that was requested. The directory "spatial" contains any spatial data that was requested. Note that spatial data is not required or recommended (due to large file sizes) for WEPS or SWEEP. It is possible to request tabular data from the Soil Data Mart without including the corresponding spatial data, and vice versa.

Tabular data is provided as a set of ASCII delimited files. Each file corresponds to a table in the SSURGO 2.1 data model. The tabular data isn't particularly useful until it has been imported into the MS Access SSURGO template database. Current Soil Data Mart downloads include a template database. If a template database was not included in the export file, you can download one from the following URL:

http://soildatamart.nrcs.usda.gov/templates.aspx

To import tabular data, load the template file into MS Access. A 'SSURGO Import' screen will display, asking for the full path to the tabular data directory (Fig. 13). Type (or cut and paste) the full path of the tabular directory and click 'OK'. A list of database tables will appear and a folder will be created in the top level directory. The folder will have the base name (non-extension part) of the template name. At the same time, an MS Access database file (*.mdb), which contains the data required for WEPS, will be created in the template folder. To import more than one soil survey area into a single MS Access database, run the Import macro specifying the full path to the directory the SSURGO data was unzipped into. Repeat the Import macro for each area desired. When done, save the template database with the imported data to a new name (*.mdb).

The SWEEP interface extracts data from the following SSURGO data files located in the \tabular directory:

chfrags.txt

chorizon.txt

chtexgrp.txt

comp.txt

crstrcts.txt

legend.txt

mapunit.txt

muaggatt.txt

version.txt

If multiple soil survey areas are imported into a single MS Access database, the database may become very large. To reduce the size of the Access database file, one may run the Export macro and delete the SSURGO data (*.txt) files created in the tabular directory that are not listed above before importing into a template Access database.

Residue Cover Estimation

These photographs (Figs. 14 - 20) may be used as a guide to determine relative residue flat cover diagonal tape is approximately 4ft 6 in. values. These photos were taken at an oblique angle to provide an image similar to that seen by an observer standing a few feet from the plot. The diagonal tape in the photographs is approximately 1.37 meters (4.5 ft).

Random Roughness Estimation

This section contains descriptions of soil surface random roughness, defined as the standard deviation of the elevation from a plane across an area (mm). Random roughness does not take into account oriented roughness. Random roughness is primarily the result of aggregate size distribution, but is also affected by various types of tillage tools. Random roughness values for typical agricultural management operations are listed in Table 1. Photographs (Figs. 21 - 29) can also be used as a guide to determine relative random roughness values. These photos were taken at an oblique angle to provide an image similar to that seen by an observer standing a few feet from the plot. The sides of the frame in the photographs is 1 meter (3.28 ft).

Table 1.	Random roughness values for typical management operations based on a silt loam soil (Ag. Handbook 537).

Field Operation	Random Roughness

(inches)

Field Operation	Random Roughness

(inches)

Chisel, sweeps

1.2	Fertilizer applicator,

anhydrous knife

0.6
Chisel, straight point	1.5	Harrow, spike	0.4
Chisel, twisted shovels	1.9	Harrow, tine	0.4
Cultivator, field	0.7	Lister	0.8
Cultivator, row	0.7	Manure injector	1.5
Cultivator, ridge till	0.7	Moldboard plow	1.9
Disk, 1-way	1.2	Mulch threader	0.4
Disk, heavy plowing	1.9	Planter, no-till	0.4
Disk, Tandem	0.8	Planter, row	0.4
Drill, double disk	0.4	Rodweeder	0.4
Drill, deep furrow	0.5	Rotary hoe	0.4
Drill, no-till	0.4	Vee ripper	1.2
Drill, no-till into sod	0.3

SWEEP Command Line Options

Input parameters for SWEEP that must be provided for the simulation period include the field and barrier dimensions, as well as biomass, soil, hydrology, and weather parameters. Wind speed can be entered either as Weibull distribution parameters or listed as average wind speeds for each time period throughout the day. Command line options may be set through the "Files" tab on the "Configuration" panel accessible under the "Tools" menu. Options not specified are set to default values internally in the model. Valid command line options for SWEEP are:

Command Line Options

Usage:	tsterode -i"input_filename" -x# -y# -t# -u -E -Plot -? -h

Valid command line options:

-? or -h	Display the available command line options.

-x#	Number of grid points in x direction (min. = 3; max. = 500). The submodel calculates the loss/deposition over a series of individual, equal-sized grid cells representing the entire simulation region. The more grid points, the smaller the area in each grid cell. The recommended total number of grid cells is 30 for a field without a barrier and 60 for a field with a barrier. Increasing the number of grid cells increases the accuracy of the soil loss/deposition estimates, as well as increases the run time. If not specified, the number of grid points is calculated within the model.

-y#	Number of grid points in y direction (min. = 3; max. = 500). The submodel calculates the loss/deposition over a series of individual, equal-sized grid cells representing the entire simulation region. The more grid points, the smaller the area in each grid cell. The recommended total number of grid cells is 30 for a field without a barrier and 60 for a field with a barrier. Increasing the number of grid cells increases the accuracy of the soil loss/deposition estimates, as well as increases the run time. If not specified, the number of grid points is calculated within the model.

-t#	Interval for surface updating in seconds (min. = 60 seconds; max. = 86400 seconds). This is used to specify a fixed surface updating interval and is primarily for testing and evaluation purposes. Because the erosion code contains an update loop dependent upon the number of time intervals/day and an inner loop that allows more frequent surface updating to occur, the interval must be evenly divisible into both the number of time intervals/day and 24 (hours in a day). If these conditions are not met, the program aborts with an error message.

-u	Disable erosion surface updating.

-i"input_filename"	Specify input filename. The input filename must be specified and listed before the -Einp, -Erod, -Egrd, and -Emit options. Quotes are required if spaces are within the file name.

-Einp	Writes (echos) the input file to "input_filename.einp". This is useful for debugging purposes. The "input_filename" is the same name as the input filename with a ".eimp" extension, and will be created in the same directory specified for the input filename.

-Erod	Output erosion summary (kg/m2) (positive values are soil loss). The one line output in the file contains the following: Total loss, saltation plus creep, suspension, PM10, and the input filename.

The "-Erod' option requires that the input file (-i"input_filename") be specified as a command line argument before the "-Erod" option, e.g.:

tsterode -iinput_filename.ext -Erod

The "input_filename" in the erosion summary is the same name as the input filename with a ".erod" extension, and will be created in the same directory specified for the input filename.

-Egrd	Output grid summary results (kg/m2) (positive values are soil loss). The "-Egrd' option requires that the input file (-i"input_filename") be specified as a command line argument before the "-Egrd" option, e.g.:

tsterode -iinput_filename.ext -Egrd

The "input_filename" in the grid summary is the same name as the input filename with a ".egrd" extension, and will be created in the same directory specified for the input filename.

-Emit	Output hourly erosion results (kg/m2) (positive values are soil loss). The "-Emit' option requires that the input file (-i"input_filename") be specified as a command line argument before the "-Emit" option, e.g.:

tsterode -iinput_filename.ext -Emit

The "input_filename" in the hourly erosion results is the same name as the input filename with a ".emit" extension, and will be created in the same directory specified for the input filename.

-Eplt	Enable printing of a file that can be used to plot various data. The data is appended to the file for each run.

-Esgrd	Output all grid cell values for selected grid cell variables (e.g., RR, ridge ht, friction velocity, etc.) as well as the standard erosion results for each subdaily period. Each "period" is identified by the "yy mm dd hr variable_name_title" prior to the grid cell values. The "-Esgrd' option requires that the input file (-i"input_filename") be specified as a command line argument before the "-Esgrd" option, e.g.:

tsterode -iinput_filename.ext -Esgrd

The "input_filename" in the grid summary is the same name as the input filename with a ".sgrd" extension, and will be created in the same directory specified for the input filename.