WEPS Glossary and Definitions
Abrasion
Breakdown of clods, crusts, and plant material by the impact of saltating soil particles moved by the wind in saltation. The impacting particles may also abrade. Abrasion causes soil aggregates to break down progressively as wind erosion continues.
Aggregation, Soil	
The cementing or binding together of soil particles into a secondary unit, aggregate, or granule.
Air-Dry Weight	
Weight of a substance after it has been allowed to dry to equilibrium with the atmosphere.
Available Water Holding Capacity
The capacity of a soil to hold water in a form available to plants, usually expressed in inches of water per inch of soil depth. Commonly defined as the amount of water held between field capacity and wilting point.
Avalanching
The increase in rate of soil flow with distance downwind across an area being eroded by wind.
Calcareous Soil
Soil containing sufficient free calcium carbonate or magnesium carbonate to effervesce visibly when treated with cold 0.1 N hydrochloric acid. High content of lime (up to about 5 percent), particularly in the clay fraction, appreciably increases erodibility by wind.
CLIGEN
CLIGEN is the weather generator developed for the Water Erosion Prediction Project (WEPP) model. It is used with WEPS to generate an average annual air temperature as well as daily precipitation, maximum and minimum temperatures, solar radiation, and dew point temperature.
Climatic Erosivity
The relative influence of climate on field erodibility by wind in different regions, specifically the effects of average wind-speed and effective soil surface moisture.
Clod			
A compact, coherent mass of soil greater than 2 millimeters in equivalent diameter often created by tillage or other mechanical disturbance of the soil.
Coarse Fragments	
Rock or mineral particles greater than2 millimeters in diameter.
Critical Wind Erosion Period
Period of the year when the greatest amount of wind erosion can be expected to occur from a field under an identified management system. It is the period when vegetative cover, soil surface conditions, and expected erosive winds, result in the greatest potential for wind erosion.
Crop Residue Management	
Maintaining stubble, stalks, and other crop residue on the soil surface or partially incorporated into the surface layer to reduce erosion, conserve soil moisture, and improve soil tilth.
Crop Tolerance to Wind Erosion
The maximum wind erosion that a growing crop can tolerate, from crop emergence to field stabilization, without an economic loss to crop stand, crop yield or crop quality. 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.
Crust			
A thin surface layer, where aggregates are bound together and the surface is sealed. It is more compact and mechanically stable than the soil material immediately beneath it. Crust is characterized by its dense, platey structure, which becomes less distinct with depth until it merges with the soil below. Crust is a transitory condition.
Deposition
The accumulation of eroded soil material on the land surface when the velocity of the transporting agent (wind or water) is reduced.
Desert Pavement
A non-erodible soil surface devoid of erodible materials or consisting of gravel or stones left on the land surface. It occurs in desert regions as a result of the removal of fine materials by wind or water erosion. Desert pavement is virtually non-erodible.
Detachment
The removal of transportable fragments of soil material from the soil mass by an eroding agent, usually falling raindrops, running water, wind, or windblown soil particles. Detachment is the process that makes soil particles or aggregates available for transport.
Drought Year
Any year when precipitation is less than 80 percent of the long-term normal.
Dry Aggregate
A compound or secondary air-dry soil particle that is not destroyed by dry sieving.
Dryness Index
The ratio of net solar energy received at the surface to the energy needed to evaporate the total precipitation received at the same site. If the dryness ratio is 2.0, then twice as much energy is available as is needed to evaporate the precipitation received. Therefore, the soil surface would be relatively dry much of the time and plants would suffer water deficits periodically without supplemental irrigation. As the index gets larger, soil surface dryness and plant water stress intensify.
Dust Storm	
A strong turbulent wind carrying large amounts of soil particles in suspension.
Empirical Model
 Values rely on experience and observation without reference to scientific principles.
EPIC
The Erosion Productivity Calculator (EPIC) crop growth model simulates a variety of crops and plant communities while accounting for nutrient and water stresses. It calculates daily production of masses of roots, leaves, stems, and reproductive organs and also leaf and stem areas. The WEPS CROP sub-model was adapted from EPIC.
Erosive Wind Energy (EWE)
The capacity of winds above the threshold velocity to cause erosion, based on the cube of wind-speed and the duration of erosive winds (greater than 8 m/s).
Erosive Wind Energy (EWE) Distribution
The weighted distribution of erosive wind energy over time at any geographic location.
Fibric Organic Soil Materials
The least decomposed of all the organic soil materials containing very high amounts of fiber that are well preserved and readily identifiable as to botanical origin.
Hemic Organic Soil Materials
Intermediate in degree of decomposition between the less decomposed fibric and the more decomposed sapric materials.
Isoline
A line on a map or chart along which there is a constant value of a variable such as wind velocity or climatic erosivity.
Isolated Field
A field where the rate of soil flow is zero at the windward edge of the field due to the presence of a stable border. An isolated field is not protected by barriers and is exposed to open wind velocities. The Wind Erosion Equation applies to conditions on an isolated field.
Knoll
An abrupt change in topography, characterized by windward slope change greater than 3 percent and windward slope less than 500 feet long.
Knoll Erodibility
The increase in wind erosion potential resulting from the compression of wind flow-lines and accompanying increased velocity over the crest of knolls. A knoll erodibility factor is used to adjust estimated erosion where these conditions occur.
Loess
Soil material transported and deposited by wind, consisting predominantly of silt-sized particles.
Management Period
A period of time during a cropping sequence when cover and management effects are approximately uniform or otherwise result in uniform rates of erosion during the period.
MOSES
Modular Soil Erosion System interface for all erosion prediction models
Organic Soil
A soil that contains a high percentage (greater than 20 percent) of organic matter throughout the solum.
Oven-Dry Weight
The weight of a substance after it has been dried in an oven at 105 degrees C, to equilibrium.
PM-2.5
 Airborn "fine particulates" less than 2.5 microns in size. PM-2.5 pariculates are small enough to be taken into the body's respiratory system, are difficult or impossible for the lungs to expel and have been linked to a number of respiratory problems. Agriculture is usually a small part of PM-2.5 pollution. EPA has stated that about half of the PM-2.5 pollution takes the form of "secondary particles". These particles form in the atmosphere when emissions of sulfur dioxide (SO2) and oxides of nitrogen (NOx) react with ammonia. The main sources of SO2 are the burning of fossil fuels in boilers at power plants and other facilities. The main sources of NOx are industrial smokestacks or power plant boilers and vehicle exhaust.
PM-10
Airborn particulates less than 10 microns in size. The 1990 Federal Clean air Act made states responsible for monitoring and controlling the amount of small airborne particulates (PM-10). PM-10 pariculates are small enough to be taken into the body's respiratory system and have been linked to a number of respiratory problems. 
Precipitation- Effectiveness (PE) Index
An index of the effectiveness of precipitation, calculated from mean monthly precipitation and mean monthly temperature at a specific geographical location. A modified P-E index is used to represent effective surface soil moisture in calculation of the WEQ climatic factor C.
Preponderance
A ratio which expresses how much of the erosive wind energy occurs parallel to the prevailing wind erosion direction, as compared to the amount of erosive wind energy occurring perpendicular to the prevailing direction. A preponderance of 1.0 indicates that as much wind erosion force occurs perpendicular to the prevailing direction as occurs parallel to that direction. A higher preponderance indicates more of the force is parallel to the prevailing wind erosion direction.
Prevailing Wind Direction
The direction from which winds most commonly occur. This may not be the same as the prevailing wind erosion direction.
Prevailing Wind Erosion Direction
The direction of erosive winds where there is potential for the greatest amount of soil to be moved, relative to the erosive force of winds from other directions.
Process Based Model
-Scientific- a particular method of making of doing something in which there are a number of scientific steps.
Random Roughness
Random roughness is the non-oriented surface roughness that is sometimes referred to as cloddiness. Random roughness is described as the standard deviation (in inches) of the soil surface elevations, measured at regular intervals from a fixed, arbitrary plane above a tilled soil surface, after oriented (ridge) roughness has been accounted for. Random roughness is usually created by the action of tillage implements.
Reference Condition
A standard wind tunnel condition for small grain equivalent determination where small grain stalks 10 inches long are lying flat on the soil surface in l0-inch rows which are perpendicular to the wind direction, with stalks oriented parallel to the wind direction.
Relative Field Erodibility
An index of relative erodibility under field conditions. Wind tunnel erodibility is adjusted for the effect of unsheltered distance and of the resistance of soil textural classes to breakdown of surface crusts by abrasion and avalanching. Compared to the wind tunnel, erodibility of a field surface is greater because the longer unsheltered distance allows abrasion and avalanching to occur.
Ridge Roughness
The degree of oriented roughness is determined by the height and width of ridges formed by tillage and planting implements or by any other means of creating systematically spaced ridges. Ridges provide sheltered zones that trap moving soil particles.
Saltation
Soil movement in wind where particles skip or bounce along the soil surface in response to wind forces. Particles in the size range from 0.1 to 0.5 mm (0.004 to 0.02 in) usually move in this manner.
Sapric Organic Soil Materials
The most highly decomposed of the organic materials, having the highest bulk density, least amount of plant fiber, and lowest water content at saturation.
Soil Discharge
The mass of soil moving perpendicular to a vertical plane per unit width of the plane per unit time 
[M/ (W T)]. eg. tons/100 ft. wide/year 
Soil Flux
 The mass of soil moving perpendicular to a unit area of a plane per unit time [M/(L2 T)]. eg. tons/ac/yr.
If the plane is vertical, then the soil flux direction is horizontal; 
If the plane is horizontal, then the soil flux direction is vertical. 
(Also see "Soil Discharge") 
Soil Loss Tolerance (T)
T is expressed as the average annual soil erosion rate (tons/acre/year) that can occur in a field with little or no long term degradation of the soil resource thus permitting crop productivity to be sustained for an indefinite period of time.
Soil Surface Moisture
Adsorbed water films surrounding surface soil particles which increase the soil resistance to erosion. In developing the climatic factor (C), soil surface moisture is assumed to be proportional to the Thornthwaite Precipitation-Effectiveness (P-E) Index.
Sorting
Separation of various size classes of soil particles or aggregates during wind erosion. Soils tend to have an increased coarseness fraction in response to continued sorting by erosion.
Spatial Information
Relating to, occupying, or of the nature of space.(from dictionary)Larry Wagner will add to definition 
Stable Border
A stable border defines the upwind boundary of an isolated field. It is an area with sufficient protection to prevent saltation from starting, and capable of trapping and holding incoming saltation from eroding areas upwind, thus preventing saltating soil particles from entering areas downwind.
Surface Armor
A layer of coarse fragments or other non-erodible particles resistant to abrasion that remain on the soil surface after the removal of fine particles by erosion.
Surface Creep
Soil movement in the wind whereby the coarser fractions are transported by rolling and sliding along the ground surface, primarily by the impact of particles in saltation rather than by direct force of the wind. Particles greater than 0.5 mm (0.02 in) in size are usually moved in this manner.
Suspension
Soil movement in wind whereby the finer fractions are transported over long distances floating in the wind-stream. Suspension is usually initiated by the impact of saltating particles. Particles moving in this manner are usually less than 0.1 mm (0.004 in) in size. Many suspension-size particles are created by abrasion during erosion.
Temporal Values
 Temporary (transient/ephemeral) conditions of the soil, climate, plants, crop residue, roughness, etc. that have an effect on the erodibility of an area, at a point in time.
Threshold Velocity
The minimum velocity at which wind will begin moving soil particles. From a smooth, bare, non-crusted surface, the threshold velocity is usually considered to be 13 mph at 1 foot above the soil surface, or 20 mph at 30 feet height.
Tilth, Soil
The physical condition of the soil in its relation to plant growth and hence must take cognizance of all soil physical conditions that influence crop development. Tilth depends on soil granulation and its stability (soil workability) as well as organic matter content, friability, moisture content, porosity, water retention, degree of aeration, root penetration, rate of water infiltration, drainage, and capillary-water capacity.
Transport
The movement of detached soil material across the land surface or through the air by wind or running water. Transport of soil particles in wind is by three modes: (l) saltation, (2) suspension, and (3) surface creep.
Transport Capacity
The maximum amount of soil material that can be carried by wind in saltation/creep under given conditions.
Trap Strip
A strip of grass or other erosion-resisting vegetation, planted between cultivated strips or fields and having sufficient width, height, and density to trap and store incoming saltation. Trap strips are usually not tall enough to create significant barrier effects.
Unsheltered Distance
The distance across an erodible field, measured along the prevailing wind erosion direction, beginning at a stable border on the upwind side and continuing downwind to a non-erodible or stable area, or to the downwind edge of the area being evaluated.
Unsheltered Field
A field or portion of a field characterized by the absence of windbreaks or barriers and fully exposed to open wind velocity.
Vegetative Wind Barrier
Narrow strips of annual or perennial vegetation planted at intervals across fields for wind erosion control, snow management, or protection of sensitive crops. Barriers have sufficient height and density to create a sheltered zone downwind. In the protected zone, wind velocities are reduced enough to prevent saltation from beginning. Vegetative barriers may also trap incoming saltation, but this is a secondary function
WEPS
Wind Erosion Prediction System that is a process- based, daily time-step, model that simulates weather, field conditions, and erosion.
Wide Field
Any field with sufficient width to allow the rate of saltation/creep flow to reach the maximum that an erosive wind can sustain. This distance is the same for any erosive wind. It varies only and inversely with erodibility of the field surface. That is, the more erodible the surface, the shorter the distance in which maximum flow is reached.
Windbreak
A living barrier of trees or combination of trees and shrubs designed to reduce wind erosion, conserve energy or moisture, control snow deposition, or provide shelter for livestock or wildlife. When used to control wind erosion, windbreaks deflect wind forces and reduce wind velocity in the downwind sheltered zone below the threshold required for initiation of soil movement.
Wind Erodibility Group
A grouping of soils that have similar properties affecting their resistance to wind erosion.
Wind Erosion
The detachment, transport, and deposition of soil by wind.
Wind Erosion Direction Factor
A numerical factor used to calculate the equivalent unsheltered distance. The factor accounts for field shape (length/width ratio), field width, preponderance, and angle of deviation of the prevailing wind erosion direction from a line perpendicular to the long side of the field or strip.
Wind Erosion Equation (WEQ)
An equation used to estimate wind erosion and design wind erosion control systems. E = f(IKCLV) wherein E is the average annual soil loss expressed in tons per acre per year; I is the soil erodibility; K is the soil ridge and random roughness factor; C is the climatic factor; L is the equivalent unsheltered distance across the field along the prevailing wind erosion direction; and V is the equivalent vegetative cover.
WINDGEN
Weather generator, developed specifically for WEPS, that simulates wind direction and maximum and minimum wind speeds on a daily basis.
Wind Stripcropping
A method of farming whereby erosion-resistant crop strips are alternated with strips of erosion- susceptible crops or fallow. Erosion-resistant strips reduce or eliminate saltation and act as soil traps designed to reduce soil avalanching. Strips are perpendicular, or nearly so, to the direction of prevailing erosive winds during critical periods.
Wind Tunnel
A duct in which experimental situations are created and tested by exposure to air-streams under controlled conditions. Both laboratory and portable field wind tunnels are used in wind erosion research.
Wind Tunnel Erodibility
An index of relative erodibility under wind tunnel conditions. Tunnel erodibility accounts for the effect of wind tunnel percent clods >0.84 mm, and for crop residue and surface roughness factors. Because wind erosion is limited by the length of the tunnel, tunnel erodibility does not account for the resistance of soil textural classes to abrasion and avalanching.
 
 
