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NREM 301NREM 301ErosionErosion
D G B l dD G B l dDr. Greg BrulandDr. Greg Bruland
Geologic Geologic vsvs Accelerated Erosion WarmAccelerated Erosion Warm--UpUp1 2 3
www.wildmadagascar.org
4 5 6
Photo courtesy of Jim MansfieldPhoto USDA NRCS
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2Photo USDA NRCS
Water Erosion
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Photo courtesy of USDA NRCS
Detachment
D t h t &Detachment & Transport
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5Zones of erosion & deposition in Guilin, ChinaZones of erosion & deposition in Guilin, China
6Mississippi Delta, MSMississippi Delta, MS
7South Shore Moloka‘iSouth Shore Moloka‘i
Types of Water Erosion
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Streambank erosionStreambank erosion
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USLE
A = R x K x LS x C x PWhere:A = Estimated Avg. Annual Soil Loss (T/ac-yr)R = Rainfall ErosivityK S il E dibili
Walter Wishmeier
K = Soil ErodibilityLS = Slope Length & SteepnessC C M tC = Cover-ManagementP = Supporting-Practice
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Components of USLEp
Rainfall Erosivity Factor (R)Rainfall Erosivity Factor (R)
A = R x K x LS x C x PA R x K x LS x C x P
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http://serc carleton edu/NAGTWorkshops/visualization/collections/soil erosion html
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http://serc.carleton.edu/NAGTWorkshops/visualization/collections/soil_erosion.html
(Troeh et al. 2004)
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Soil Erodibility Factor (K)Soil Erodibility Factor (K)
• Inherent soil erodibilityInherent soil erodibility• Rate of soil loss on a standard plot (72.6 ft
long on a 9% slope)long on a 9% slope)
A = R x K x LS x C x PA = R x K x LS x C x P
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K factors are t b l t d f h iltabulated for each soil map unit in County Soil Surveys. y
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K factor nomograph: K = (5 soil properties)
(Troeh et (al. 2004)
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Slope Length & SteepnessSlope Length & Steepness Factor (LS)
LS is the ratio of expected soil loss per unit area of a particular field segmentunit area of a particular field segment compared to what would be lost from a 9% 72 6-ft-long slope with no cover9%, 72.6 ft long slope with no cover
A = R x K x LS x C x P
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LS Lookup Tables
Example: Determine LS for ag field w/ slope of 5% & length of 400 ft.
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Cover-Management Factor (C)Cover Management Factor (C)
A = R x K x LS x C x PA = R x K x LS x C x P
C = (5 subfactors)C = (5 subfactors)
C = PLU*CC*SC*SR*SM
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Supporting-Practice (P) FactorSupporting Practice (P) Factor
• The fractional amount of erosion thatThe fractional amount of erosion that occurs when “special practices,” i.e. contour cultivation contour strip croppingcontour cultivation, contour strip cropping, & terracing, are used compared with erosion that would occur without themerosion that would occur without them.
A = R x K x LS x C x P
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Example USLE Calculations
With conventional tillage:A= 170 x 0.26 x 1.62 x 0.20 x 1.0 = 14.3 t/a/yy
With conservation tillage:A = 170 x 0.26 x 1.62 x 0.11 x 1.0 = 7.9 t/a/y
With contour cultivation:With contour cultivation:A= 170 x 0.26 x 1.62 x 0.20 x 0.61 = 8.6 t/a/y
With cons. tillage & contour cult.:A = 170 x 0 26 x 1 62 x 0 11 x 0 61 = 4 8 t/a/y
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A 170 x 0.26 x 1.62 x 0.11 x 0.61 4.8 t/a/y
Onsite: Gullying
28(www.wildmadagascar.org)
Offsite
High sediment loads in the Manambolo River (www.wildmadagascar.org)
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Betsiboka River & estuary, image from Space Shuttle (NASA)
Water Erosion BMPs
1) Strip cropping) p pp g
2) Grassed waterways
3) Terraces3) Terraces
4) Conservation tillage
) ff5) Riparian buffers
30Photos courtesy of USDA NRCS.
Wind Erosion
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Types of Wind Erosion
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http://serc.carleton.edu/NAGTWorkshops/visualization/collections/soil_erosion.html
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WEQE = (I’, K’, C’, L’, V)
Where:Where:E = Estimated Avg. Annual Soil Loss (T/ac-yr)I’ = Soil Erodibility K’ = Soil Ridge RoughnessC’ = ClimateL’ Width f fi ldL’ = Width of fieldV = Vegetative Cover
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A l SAral Sea: Shrinking since 1960 due to diversion of water from 2 rivers (Syr Darya, Amu Darya) to
(Mussner 2005)
irrigate nearby crop land
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•Salt concentration ↑ from 10 to >23‰, contributing to devastation of a once-thriving fishery.
•Local climate shifted, w/ hotter, drier summers & colder, longer winters.
•As water retreated, salty soil remained on exposed lake bed. Dust storms have blown up to 75,000 tons of this exposed soil annually, dispersing salt particles, pesticideannually, dispersing salt particles, pesticide residues.
•Air pollution caused widespread nutritional & i t il trespiratory ailments.
•Crop yields diminished.
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(Perera 1993, Micklin 1992, Rich 1991, Perera 1988, United Nations Environment Programme 1992)
Wind Erosion BMPs
1) Conservation tillage
2) Barriers/Windbreaks
3) Moisture management3) Moisture management
4) Soil amendments
38(Photos courtesy of USDA NRCS)
Erosion Models• Water: USLE, MUSLE, RUSLE, RUSLE2, EPIC,
AGNPS, WEPP
• Wind: WEQ RWEQ WEPS39
• Wind: WEQ, RWEQ, WEPS
FallTypes ofof Mass Wast
Rotational slide/slump
Wast-ing
Translational slide
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Flows
mudflow
debris flow
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