Exercises Introduction: Evaluating Wind Erosion Problems with WEPS

These exercises are designed to provide the user with step-by-step examples of some common tasks performed with the WEPS model. These exercises cover many topics including basic model operation, file management, and building and editing field management rotations within the Management/Crop Rotation Editor of WEPS (MCREW). The focus of the exercises should be on learning to use WEPS for conservation planning. Although the exercise scenarios use locations in various parts of the United States, the skills learned in each exercise are intended to build the users proficiency with WEPS that are applicable in many locations. Therefore new users are encourages to complete all the exercises regardless of location of the scenario. Since WEPS is constantly being improved and parameters modified, the results you get may not exactly match those reported in the exercises. This is not unexpected.

Note: As the WEPS model finishes a given run, it may sometimes display a warning that one or more of the crops simulated did not reach maturity. This is not uncommon, especially for crops that are harvested before reaching maturity such as forage crops. If such a message is obtained, click "OK" to complete the run. If most of the years crops reach about 95% maturity the run is OK to use. However, if many of the years crops are lower than 95%, check to make sure planting and harvesting dates for the crop are as expected for the location being simulated. If it still does not reach 95%, contact the Natural Resources Conservation Service (NRCS) Database Manager or NRCS Wind Erosion Specialist. The user should resolve such maturity issues for crops that are harvested after reaching maturity.

Definitions and Considerations

Projects and Runs: A "WEPS Project" is a directory that can be thought of as a working area where WEPS simulation runs are created and stored. A project stores all the parameters and files for the current simulation run being prepared within the WEPS interface, as well as any past WEPS simulation runs. For example, a particular project may represent a directory for an individual farm under which all the simulation runs for each field and management alternatives on that farm are stored. When a project is saved, all of the information contained on the current interface screen is stored in the project directory. Multiple WEPS projects can be created and given various names by the user. One can also remove unnecessary WEPS project and run directories from within the WEPS interface via the pertinent options under the "Project" menu. A Project directory can be accessed through the Project menu and Project management or soil files accessed through their respective Project folder icon .

A "WEPS Run" refers to a single simulation of a field with all associated input and output files. Each run is stored in a separate folder or subdirectory which by default is located under the current WEPS project directory. A WEPS run subdirectory is created every time a simulation run is made. A WEPS run subdirectory stores a copy of all input files used to make the simulation run, together with the output files generated from those inputs. Thus, one is able to recall the identical WEPS run at a later date (and presumably get the same outputs when using the same version of WEPS 1.0 and the weather generators/databases) because the original input files are still available. Typically, 're-running' a previous run is not necessary since the outputs are stored in the run directory and can be reviewed via the ViewOutput menu. However, if additional outputs not generated with the original run are desired, it will be necessary to load the previous run and re-run it using the desired output options. The run directories make it relatively easy to archive or remove WEPS runs as alternative erosion planning scenarios are tested for a field or farm. If, for example, a change is made to create a different management alternative, all the information pertaining to this new scenario will be saved to a new subdirectory under a new WEPS run name, when the simulation is made.

File and project naming in WEPS should be considered carefully. Management or project names should be long enough to uniquely describe them but not so long so that the name is difficult to view in file chooser windows. Some special characters are not allowed in file or directory names used in WEPS. Known characters that are not allowed or recommended include: @ ? ' ` & ~ / \ < > | : * "

Templates: A "Template" is a pre-built management rotation file or soil file. Management templates are accessed through the Management Template folder icon and are intended to be used as a template from which to create other management files and saved to a different name and location. Soil templates are NRCS Soil Survey Geographic (SSURGO) database files and individual soils are accessed through the Soil Template folder icon . It is recommended that the user not edit or otherwise change template file or names.

Simulation Region Orientations and Angles: Field orientation and direction of tillage within the simulation region in WEPS are independent and measured relative to true North (0 degrees). Angles are important in WEPS because wind directions are simulated to mimic the historic wind direction distribution for the selected location. As such wind direction varies from day to day and therefore erosion losses will also vary relative to field angle or ridge orientation. The field orientation in WEPS should be rotated to represent the actual orientation on the landscape. Note that the field will only rotate in a range of ±45 degrees. By rotating and adjusting the field length and width, the user should be able to obtain the desired field size and orientation for a field. Tillage direction should also be entered relative to true North. For example, if a rectangular field has its long side oriented 20.0 degrees from true North and tillage is performed parallel to that long side of the field, the tillage direction should also be entered as 20.0 degrees within the Management Editor.

Plant Damage: Although soil loss is the primary concern in wind erosion, damage to plants should also be considered. Crops can be damaged by blowing soil particles, exposure of plant roots, burial of plants by drifting soil, or desiccation and twisting of plants by the wind. In several exercises, we will examine and take into account the crop tolerance to blowing soil. The NRCS has published a table listing the tolerance of various crops to blowing soil (USDA-
NRCS,2000; National Agronomy Manual; Table 502-4, pg 502-19). This table should be referred to as needed during the exercises (Table 1.1). Crops can tolerate greater amounts of blowing soil than shown, but yield and quality may be affected adversely.

Table 1.1	Crop tolerances used by Natural Resource Conservation Service (NRCS) to design wind erosion control methods (USDA-NRCS, 2000).

Tolerant #	Moderate Tolerance	Low Tolerance	Very Low Tolerance
"T"	2 ton/ac	1 ton/ac	0 to 0.5 ton/ac
Barley	Alfalfa (mature)	Broccoli	Alfalfa (seedlings)
Buckwheat	Corn	Cabbage	Asparagus
Flax	Onions (> 30 days)	Cotton	Cantaloupe
Grain Sorghum	Orchard Crops	Cucumbers	Carrots
Millet	Soybeans	Garlic	Celery
Oats	Sunflowers	Green/Snap Beans	Eggplant
Rye	Sweet Corn	Lima Beans	Flowers
Wheat	Peanuts	Kiwi Fruit
Peas	Lettuce
Potatoes	Muskmelons
Sweet Potatoes	Onion (seedlings)
Tobacco	Peppers
Spinach
Squash
Strawberries
Sugar Beets
Table Beets
Tomatoes
Watermelons
# Crop tolerance is defined as the maximum wind erosion that a growing crop can tolerate, from crop emergence to field stabilization, without an economic loss to stand, yield, or quality.

Reference:

USDA-NRCS. 2000. National Agronomy Manual, Part 502-Wind Erosion, 190-V NAM. 3rd Edition. Washington, D. C.