WIND EROSION EQUATION Recent Changes (NAM) USDA-NRCS - PowerPoint PPT Presentation

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WIND EROSION EQUATION Recent Changes (NAM) USDA-NRCS. Wind Erosion continues to be a serious problem in the semiarid and arid regions of the US. The Good Old Days. The Good Old Days cont. WEQ Changes made!.

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Wind erosion equation recent changes nam usda nrcs l.jpg


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  • Wind Erosion continues to be a serious problem in the semiarid and arid regions of the US.

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The Good Old Days

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The Good Old Days cont.

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WEQ Changes made!

  • WEQ has been updated to account for irrigation effects, random roughness and I Factor adjustments.

  • WEQ changes are outlined in the new edition of the National Agronomy Manual.

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Introduction WEQ Excel Spreadsheet

  • Cover NAM changes

  • Changes to Ridge Roughness

  • Addition of Random Roughness

  • Quick intro to the Excel spreadsheet

  • Demo how to edit and make changes

  • Answer Questions

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Spreadsheet History

  • Began as a spreadsheet by Tom Keep

  • Then Circular 2, NAM amendment Sept. 12, 1997 was incorporated

  • SGe calculations added, 1998

  • Krd-Ridge Roughness formulas added in 1998

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Circular 2 Changes

  • I Adjustment for Irrigation

    -Above 180 no adjustment

    -180 or less, reduce one I class

  • IF – ‘Irr. Factor’ reduces Erosive Wind Energy (EWE) for mgt period

  • Random Roughness (Krr) combined with Ridge Roughness (Krd)

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  • Irrigation adjustment (IF)

    -adjustment applies to all soils

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  • Effects of wet soil is accounted for by adjusting the EWE for the mgt period

  • Bare wet soil remains non-erodible wet:

    • 1 day for coarse textured soils

    • 2 days for medium textured soils

    • 3 days for fine textured soils

  • See sheet “WEG tab” for table

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  • Soil cloddiness raises the threshold wind speed at which erosion begins

  • Provides sheltered area among clods where moving soil can be trapped

  • Spreadsheet reduces RR (clodsize) by one half after 15 days.

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  • Non-oriented surface roughness

    • Cloddiness

  • Usually created by tillage implements

  • Values represented as standard deviation, in inches, of roughness heights

  • Use Random Roughness-Guidance sheet

  • Roughness assigned to each tillage implement (ideal conditions)

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Random Roughness - Krr

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Ridge Roughness- Krd

  • Revised NAM has new tables

  • Based on I values and Preponderance

  • Low Preponderance values indicate less of the erosive wind is from the prevailing wind direction.

  • Higher Krd values indicate that ridges are less effective

  • Krd can be lower than 0.5 now

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Irrigation Input Requirements

  • Enter the number of Irrigations, including pre-plant and post harvest irrigation

  • “Non-erodible wet days” will be calculated based on soil texture (WEG)

  • Drip irrigation poses a problem. Need to estimate the % of surface that is non-erodible wet

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Circle Irrigation

The soil texture determines the number of non-erodible wet days (1,2,or 3) per irrigation

It takes this system 96 hours to make one complete circle. For WEQ this is one irrigation.

Day 3-24 hrs

Day 4-24 hrs

Day 1-24 hrs

Day 2-24 hrs

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Field Width

  • With the WEQ Speadsheet, field width is the distance across the short side of the field or average short side of a polygon.

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Field Width vs Unsheltered Distance



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Field Width vs Unsheltered Distance

  • The Excel Spreadsheet model will determine L using the length/width ratio of the field, the angle of deviation, wind preponderance and the resulting wind erosion direction factor.

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Computer Requirements

  • Need 486 minimum.

  • 586 is better

  • Windows 95, 98, or NT

  • Excel version 7.0

  • 16 mg of RAM or better

  • File name WEQvs8.01.xls

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INSTR sheet

  • Wind Erosion Model Worksheet Legend


  • Describes input data and column headings

  • New-Krd, Krr, IF, No. of Irr, and TWF

Read this sheet first.

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Res WKS sheetRequired Inputs

  • Operation Dates

  • Crop Names

  • Operations

  • Percent Flat Residue

  • Number of irrigation per mgt period

  • Yield adjustment

  • Prod., Farm, Tract, Field, C, I, Field Width, LW ratio, Tillage Dir, Field Dir, Irr (y/n)

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Calc sheet

  • Detailed calculations by Mgt Period

  • Note Krd, Krr, and IF factors added here

  • No inputs needed or allowed

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Data Tables

  • Crop table

    -Need to maintain crop data;

    residue produced and green growth

  • Tillage table

    -Residue reduction

    -Random roughness assigned to tillage

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Data Tables cont.

  • Climate data, the wind direction, EWE, and Preponderance must be added for climate stations in your state.

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  • If Users have a basic understanding of the EXCEL spreadsheet, they can use this model.

  • State Agronomist should become familiar with the wind data (climate file), crop data, and operation (tillage) files before beginning use in a new state.

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  • We can not change tillage direction in each mgt period.

  • Need to create templates and save for later use.

  • It does not allow for crusting (no I factor adjustment for a period of crusting).

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  • Growth curve data is limited

  • Do not have SGe curves for all crops both green and dry

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Where to get more information

  • Call State Agronomists for assistance:

  • State Agronomists can call:

    Mike Sporcic, , 505-761-442


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Where to get more information

  • Gary Tibke– (785)537-5541

  • Lorenz Sutherland--(719)384-5408

  • Websites for WEQ or

We’re Done

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Questions & Short Demo END

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The End

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