Lecture 10b Soil Erosion

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Lecture 10b Soil Erosion USLE Ephesus

• Soil Erosion we do not miss the soil until it
  is gone!

D.C. Reicosky
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Geologic Erosion

• The group of natural processes (including
  weathering, dissolution, abrasion, corrosion, and
  transportation) by which material is worn away
  from the earth's surface

Badlands South Dakota
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Problems caused by soil Erosion
Evidence of Soil Erosion

• 1. Loss of valuable topsoil -
• ag land costs 1500/acre for upper 4 feet of
  soil, or 31.25/inch,(1500/48 in.)
• However- topsoil 10x more valuable than subsoil.
  
• Soil loss includes - soil nutrient water
  water holding capacity.

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Problems caused by soil erosion

• 2. Damage due to deposition
• 3. Damage to fields because gully erosion is
  reducing field size.
• 4. Pollution due to off site or Non-Point
  Pollution 3-18 Billion per year or 50.00
  per acre if 1/2 the farmland is a problem
• Pollution sediment, nutrients, pesticides

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Problems caused by erosion
Loss of Topsoil Productivity Decline

• 5. Steady but slow productivity decline
• 2.5 inches lost 5-15 productivity decline.
• 5 inches lost 10-35 productivity decline.

Topsoil is covered by sediments from upslope
Sediments
Original Ap
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THE DROP!!!
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The Drop
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Causes of Soil Erosion

• Impact of RAIN DROPS -
  fall at 20 mph
  
  
  
  

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Raindrops cause

• Soil particles are separated
  due to beating of
  rain drops
• Surface soil pores
  fill with soil
  particles
  reducing
  infiltration.
• Surface flow begins due to lack of infiltration
  

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Erosion Types

• Sheet Erosion - thin film of water over the
  entire field moving down-slope
• Pedestal erosion - rocks on surface of soil
  protect the soil underneath and thus as the sheet
  erosion removes more soil from around the rock
  the rock is left elevated.

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Sheet Erosion
NRCS Photo

• Sheet erosion- recognized by soil deposition at
  the bottom of a slope, or by the presence of
  light - colored subsoil appearing on the surface,
  or stones left on pedestals.

Evidence of sheet erosion
Elevated rock
Purdue Univ.
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• Rill Erosion - collection of sheet erosion water
  into channels ( rills) that erode the bottom and
  side of the rill.

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Rill Erosion
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• Gully erosion - increasing size of rills
  eventually lead to a Gully or a channel too large
  for crossing by farm equipment.

Australia
Southeast Asia
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Australia
Africa
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Urban Erosion
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Sediment From land to river to estuary
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Sediment entering clean river in Montana
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G.W. Randall
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Soil Erosion Minnesota

• 55 of Minnesota has land eroded ltT, but 10 is
  4xT.
• The average daily amount of soil being
  transported downstream by the Mississippi River
  at Winona is about 302,000 tons per year or 827
  tons/day
• When more land is placed in CRP or RIM (Land
  taken out of crop production and placed in grass)
  the overall erosion rates for MN will decline as
  they did from 1982 to 1997.
• However, when more land is put in corn and
  soybeans, the erosion rates will increase.
• Is development of bio-fuels from corn a
  sustainable practice as far as the soil is
  concerned?

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Water Erosion Prediction

• Universal Soil Loss Equation (USLE)
• A R SL K C P
• R rainfall
• SL slope and length
• K soil erodibility
• C crop type
• P practices
• A soil loss

D.C. Reicosky
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Universal Soil Loss Equation USLEPredicting
soil loss.

• A RKLSCP
• A Tons of soil loss per acre per year.

D.C. Reicosky
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Rainfall Factor

• Based on intensity and quantity of rainfall
• Found in Soil Survey
• Specific to each county or state

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Soil Erodibility

• Soil erodibility factor (k)
• Based on erosion rate per unit of R for a
  specific soil in cultivated fallow on 9 slopes
  that are 72.6 ft. long.
• Found in the Soil Survey, Table 15 or 16

D.C. Reicosky
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Slope and Length

• Slope slope steepness ()
• Slope length length of slope (ft.)
• Constant 72.5
• Approx for 100m
• lt 1 0.2
• 1 lt Slope lt 3 0.3
• 3 lt Slope lt 5 0.4
• gt 5 0.5

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• For example, a 600 ft. slope with a 10 gradient
  would have an LS factor of 3.5.
• If slope is 6-12 for soil map unit use an
  average of 9 for the soil.

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Crop Management Factor-C

• The C factor is the crop management factor and is
  the ratio of soil loss compared to fallow (bare,
  exposed) soil.
• Some examples of C factors for various cropping
  systems are given

0.006
0.005

• 1.0 cont. corn or sybn, conv.T
  .30 cont. corn or
  sybn,cons.T .20 corn - oats
• .08 corn - oats - pasture .009 pasture
  poor
• .006 pasture good
• .005 woodland or forest

0.3
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P Erosion control factor, ratio of soil loss
compared to farming up and down the slope

• The P factor is the erosion control factor. If a
  farmer plows up and down the slope of a hill,
  P1. When plowing is done following the contours
  of the hill, P is reduced. P can not be used in
  pastures only cropland.

P0.45
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Tolerable level of soil loss

• Soil loss tolerance (T)
• T is the maximum level of soil erosion
  (tons/acre/year) that will permit a high level of
  crop productivity to be maintained economically
  and indefinitely

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Factors Affecting - T

• Depth of soil
• Type of parent material
• Relative productivity of topsoil and subsoil
• Amount of previous erosion

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Water Erosion Control

• Create soil condition resistant to erosion
• Protect soil
• Mechanical
• Vegetative

D.C. Reicosky
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Control Practices and Structures

• Farmer
• Reduce slope length with terraces, add grassed
  waterways for steep slopes
• Use crop rotations, change tillage practices, use
  contours

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Control Practices and Structures

• Homeowner
• Redirect water flow away from drains
• Slow water flow
• Use plants, terracing, rocks etc.
• Aeration to reduce bulk density and increase
  water infiltration

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Control Practices and Structures- Engineering
Silt Fences
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Engineering Sediment Lagoons Environmental
Plantings
http//www.bbmwd.org/tmdl.htm

• By diverting storm-water from impervious areas
  such as roofs and paths, and by reusing it
  when-ever possible, urban runoff can be greatly
  reduced.
• This can be achieved by directing rain gutters to
  landscaped areas, drywells and infiltration
  basins where water can seep into the ground.
• Environmental plantings Rain Gardens aid in
  soil retention as the water is moved from one
  area to another.

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NRCS
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Wind Erosion
E f (I, K, C, L, V)

• E potential average annual soil loss
• I soil erodibility index
• K soil ridge roughness factor
• C climate factor
• L unsheltered distance across a field
• V equivalent vegetative cover

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Factors Affecting Wind Erosion

• Cloddiness
• Crop residue
• Ridges
• Soil factors
• Barriers
• Wind velocity
• Wind direction

Iowa State
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Cloddiness

• Size
• Amount of clods
• Smaller clods erode easier
• Larger clods provide wind break

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Crop Residue

• Stature (standing or flat)
• Amount
• Type of crop
• Tillage operation

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Soil Factors

• Organic matter
• Good polysacharides glues particles together
• poor granulation small erodible particles
• CO3 content
• Promotes granulation
• Clay content
• The greater the clay the less erosion

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Ridges

• Ridges act as a wind break and cause trapping

12 degrees
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Wind speed

• The greater the wind speed the greater the
  erosion
• Erosion occurs when wind speeds are greater than
  15 mph

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Barriers

• Wind breaks
• Flax strips
• Grass strips

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Four legend categories show areas that are less
than the tolerable rate (T), from one to two
times T , rate, two to four times T rate, and
four or more times T rate.
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Challenge of Ephesus!

• Could you have helped them?
• HOW??
• http//www.sailturkey.com/panoramas/ephesus/

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The End