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Dr Greg Bruland

WEQ & Other ModelsWEQ & Other ModelsDr. Greg Bruland

NREM 461

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I. Wind Erosion Equation (WEQ)

A. WEQ developed by scientists at ARS Wind Erosion Research Unit (WERU) in Manhattan, Kansas

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B. Woodruff & Skiddoway published the formal WEQ model in 1965

1. Designed to predict annual wind erosion in the

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2. Based on laboratory & wind tunnel studiesa difficult to measure wind erosion in the fielda. difficult to measure wind erosion in the field

Portable wind tunnels for conducting field-based wind erosion research

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D W SDr. W.S. Chepil inspecting a p glaboratory wind tunnel at the ARSat the ARS Wind Erosion R hResearch Unit in Manhattan, Kansas

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WEQE = ƒ(I’, K’, C’, L’, V)

Where:

E = Avg. Annual Soil Loss (T/ac-yr)I’ = Soil erodibility factor K’ =Soil ridge roughness factorC’ = Climatic factorL’ = Width of field factorL = Width of field factorV = Vegetative cover factor

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WEQ Term Units Metric Units

E = Avg. Annual Soil Loss

tons/acre-year Metric tons/ hectare-yearLoss hectare-year

I’ = soil erodibility tons/acre-year Mt/ha-yr

K’ = soil ridgeK soil ridge roughness C’ = climate factor

L’ = width of field factor dimensionless dimensionlessV = vegetative cover lbs/ac kg/hafactor range: 0-3000 range: 0-2000

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C. WEQ Factor Notes

I’ = potential annual soil loss from a wide, unsheltered, isolated field with bare smooth uncrusted surfaceisolated field with bare, smooth, uncrusted surface

K’ = precise estimation of K’ requires a wind tunnel, b t K b d t ti t K’ b d fi ldbut Kr can be used to estimate K’ based on field roughness & Table 6-13

C’ = includes direct effects of wind velocity & indirecteffects of precipitation & temperature

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(Skidmore & Woodruff 1968)

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L’ = width of field = unsheltered distance in downwind direction.

Proportion of forces parallel to, as opposedProportion of forces parallel to, as opposed to perpendicular to, the prevailing wind direction is called preponderance factor (PF)

PF = 1,

PF = 2, twice as much force parallel to prevailing wind than perpendicular to it

Median Travel Distance (MTD) = field dimension * wind direction factor (WDF)

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V = depends on dry matter of veg its texture alive vsV = depends on dry matter of veg, its texture, alive vs dead, & standing vs flat.

1 t d t i l t titi f fl t1. converted to equivalent quantities of flat wheat straw

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D. Predicting Soil Loss with WEQStep 1: Get I & Is from tables & calculate E1

I * Is = E1

Step 2: Get Kr from table & calculate E2E2 = E1 * Kr

Step 3: Get C’ from map & calculate E3 E3 = E2 * C’

Step 4: Use MTD, E2, E3, & nomogram to determine E4E4 = E3 * ƒ(L’)

Step 5: Use R to determine V from figure. Use V & E4 to determine E5from scale

E * ƒ(V)E5 * ƒ(V)11

E WEQ Notes:E. WEQ Notes:

1. Allows interactions among factors, complex li l ti hinonlinear relationships

2. Used for periods > 1 yr

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5. Excel version & other documentation available at

http://www.weru.ksu.edu/nrcs/weq.html12

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II. Other models

A. RWEQ

1. Computerized DOS-based version of WEQ that uses data banks of info about climate, soil propertiesproperties

2. 5 factors combined to produce soil loss predictions for period of 15 days or less

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B. Wind Erosion Prediction System (WEPS)

1. 1986: Team from USDA, EPA, BLM appointed to develop WEPS as replacement for

2. Process-based, daily time-step model that predicts wind erosion via simulation of fundamental

t llicontrolling processes

3. Modular structure w/ hydrology, soil, weather, y gyerosion submodels

4 Utilizes 4 databases: climate soils4. Utilizes 4 databases: climate, soils, management, crop/decomposition

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5. Simulation area is a field or a few adjacent fields

6. Calculates soil movement, estimates plant damage, predicts PM-10 emissions when wind gspeeds exceed erosion thresholds

7 Provides users w/ spatial information regarding7. Provides users w/ spatial information regarding soil flux, deposition, & loss from field(s) over time

8 I t d d f ti l i i8. Intended for conservation planning, assessing wind erosion for NRCS's National Resources Inventory (NRI), aiding development of regional & national policy

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Comparison of Output from WEQ vs WEPS

WEQ WEPSAnnual Soil Loss ua So oss

Period Soil Loss

S /CSaltation/Creep

Suspension

PM-10

Surface Conditions

Windy Energy

Boundary LossBoundary Loss

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