1. Soil Erosion Peter Kinnell
Research area:
Rainfall erosion processes and prediction

2. Soil Erosion
Soil erosion requires particles to be plucked from a surface where they are held by gravity and other forces (interparticle friction, cohesion) and moved laterally away from the place where they were.

3. Soil Erosion Tectonics: Lifts the Earth Surface
Soil Erosion: ► Flattens the Earth Surface ► Moves soil material over the Earth Surface

4. Drivers 2 primary drivers: Wind – semi-arid and arid areas
Water – non arid areas
Gravity is involved in wind and water erosion

5. Importance of Soil Erosion by Water
Geological time
Modification of landform
Soil formation
Current time
Onsite Land degradation – loss of productivity
Offsite
Deposition of sediment on land - beneficial eg: soil fertility of flood plains - problematic eg: in buildings, on roads
Soil material in rivers affects water quality
Translocation of material over the landscape
Soil Catena

6. Geographic Distribution
Climate and soil characteristics control whether erosion occurs by wind or water
Water erosion vulnerability

7. Wind Erosion

8. Water Erosion in Arid/Semi-arid areas
Nevada, USA

9. Wind Erosion Energy required to drive erosion comes from wind
Wind speed is the wind factor normally considered
Dry non-cohesive soil material at the surface is highly susceptible to being blown by wind

10. Wind Erosion
Sahara desert
Wind driven saltation and creep

11. Wind Driven Saltation & Creep
Saltation – hop
Creep - roll

12. Very fine particles remain suspended in air
Dust
Very fine particles remain suspended in air
Wind

13. Dust
Broken Hill, NSW 22 Sept 2009

14. Dust
Sydney, NSW 23 Sept 2009

15. Wind Erosion o Soil lost per unit area Wind speed
Critical speed required for wind to overcome forces holding particles to soil surface (gravity, interparticle friction, cohesion)

16. Water Erosion
2 Drivers:
Surface Water Flow
Raindrop Impact

17. Water Erosion Channels caused by flow driven erosion
Processes similar to wind erosion
Rill Erosion
Gully Erosion

18. Flow Driven Saltation & Rolling

19. Very fine particles remain suspended in water
Suspended Load
Very fine particles remain suspended in water
Flow

20. Flow Driven Erosion
Soil lost per unit area o
Flow energy
Critical energy required for water to overcome forces holding particles to soil surface (gravity, interparticle friction, cohesion)
Raindrops impacting the soil can also overcome the forces holding particles to the soil surface

21. Raindrop impact driven erosion
Splash Erosion
Raindrop Detachment & Splash Transport (RD-ST)
On sloping surfaces more splashed down slope than up so more erosion as slope gradient increases
Detachment = the process of plucking particles held within the soil surface by cohesion and interparticle friction
Transport process limits erosion particularly on low gradient slopes
- Relatively inefficient erosion system especially on slopes with low to moderate gradients

22. Raindrop impact driven erosion
Rain-impacted flow
Transport Mechanism 1. Raindrop Induced Saltation (RIS)
Detachment by raindrop impact may be followed by
Raindrop induced saltation (RIS)
Raindrop induced rolling (RIR)
Transport in suspension (FS)
Flow driven saltation (FDR)
Flow driven rolling (FDR)
Detachment and uplift caused by raindrops impacting flow
Flow
Flow
Rain-impacted flows have more efficient transport processes

23. Raindrop impact driven erosion
Rain-impacted flow
Transport Mechanism 1. Raindrop Induced Saltation (RIS)
Particles move downstream during fall
Flow
Wait for a subsequent impact before moving again

24. Raindrop impact driven erosion
Rain-impacted flow
Transport Mechanism 2. Raindrop Induced Rolling (RIR)
Particles move downstream by rolling
Flow
Wait for a subsequent impact before moving again

25. Raindrop impact driven erosion
Rain-impacted flow
Transport Mechanism 3. Flow Suspension (FS)
Small particles remain suspended and
move without raindrop stimulation
Flow
Large particles wait
Acts at the same time as RD – RIS/RIR

26. Raindrop impact driven erosion
Rain-impacted flow
Transport Mechanism 4. Flow Driven Saltation (FDS) Transport Mechanism 5. Flow Driven Rolling (FDR)
After detachment by drop impact Coarse particles
move without raindrop stimulation
Flow

27. Raindrop impact driven erosion
Rain-impacted flow
Pedestals result from stone protecting the soil beneath them from detachment by raindrop impact while raindrop detachment and sediment transport by rain-impacted flows occurs in the surrounding area

28. Raindrop impact driven erosion
Rain-impacted flow
A lot of the soil loss is INSIDIOUS
1 mm loss from the surface on 1 km2 = 1 m x 1 m x 1km channel

29. Critical conditions for detachment and transport modes
Change in soil surface (crusting)
Erosion results from the expenditure of energy associated with both flow and raindrop impact
Flow depth effect on drop energy available for detachment

30. Critical conditions for detachment and transport modes
Raindrop detachment only occurs when the raindrop energy exceeds that needed to cause detachment
NB: Both raindrop detachment and flow detachment can operate at the same time
Splash Erosion
Flow Driven Transport
Raindrop driven erosion
Flow driven erosion
Rain Driven Transport in Flow
Coarse sand RD-RIR
Coarse sand RD-FDR
Change in soil surface (crusting)
Erosion results from the expenditure of energy associated with both flow and raindrop impact
Flow depth effect on drop energy available for detachment
Flow detachment only occurs when the shear stress needed to cause detachment is exceeded
Flow Energy
Not a 2D (X,Y) graph

31. Forms of Water Erosion on a Hillslope
Rain
Rills occupy a small proportion of the surface area
Splash Erosion, Sheet Erosion, and Interrill Erosion operate over most of the nutrient rich soil surface
Rill
Interrill
Sheet Erosion
Surface Runoff
Splash Erosion
Flow energy increasing
Rill & Interrill Erosion
River
(Gully Erosion)

32. Prediction of Rainfall Erosion
Map of climatic effect on soil loss as determined by the Universal Soil Loss Equation
The USLE is the most widely used erosion model in the world

33. Universal Soil Loss Equation
Soil Loss = f (climate, soil, topography, landuse) A = R K LS C P
A = Long term average annual soil loss (~ 20 years) caused by sheet and rill erosion
R = rainfall-runoff (erosivity) factor [CLIMATE]
K = soil (erodibility) factor
● LS = topographic factors (L re slope length S re slope gradient)
C = crop/crop management factor [VEGETATION]
P = soil conservation practice factor

34. Universal Soil Loss Equation
Soil Loss = f (climate, soil, topography, landuse) A = R K LS C P
Developed from more than 10,000 plot-years of experiments in the USA

35. Universal Soil Loss Equation
Soil Loss = f (climate, soil, topography, landuse) A = R K LS C P
C, P & L are the main factors modified by
land management
A has units of weight per unit area (t/ha)
= the amount of soil lost from a specific area divided by the area
The soil loss within that area may not be uniform the bigger the area the less likely it is to be uniform

36. Universal Soil Loss Equation
Soil Loss = f (climate, soil, topography, landuse) A = R K LS C P
Originally developed in the 1960s
The Revised USLE (RUSLE):1997
An update of the USLE to take account of new information gained since the 1960s and 70s
The mathematical form of the model remained as above but changes were made to the way in which some of the factor values are calculated

37. Universal Soil Loss Equation
Soil Loss = f (climate, soil, topography, landuse) A = R K LS C P
USLE/RUSLE used widely in the world including Australia
Catchment Erosion
Urban Erosion
State of Environment Reports
Implemented in NSW via SOILOSS computer program (Dept Land & Water Conservation, NSW)

38. Universal Soil Loss Equation
Oz Validation - 6 SCS NSW Research Stations
bare soil

39. 33m long 6% slope bare soil Cropped Plot  A1 = R K = 10 t/ha
Unit Plot
22m long
9% slope
bare soil
33m long
6% slope
Cropped Plot
Works mathematically in 2 steps: 1. Predict the loss from a control plot called the “unit” plot 2. Use factors to adjust this to predict loss from area of interest
 A1 = R K = 10 t/ha
 AC = A1 ( L S C P )
 AC = 10 (1.22 x 0.57 x 0.16 x 1.0) = 1.1 t/ha

40. R factor
The R factor is dependent on the total kinetic energy of the raindrops produced by rain during rainstorms over many (20 or so) years and the maximum rainfall intensities that occur during those storms

41. R Map for New South Wales
Erosivity increases northward along the coast
Erosivity increases from the inland to the coast

42. K: soil erodibility factor
K from field experiments:
Time - 5 years or more
Expense - setup of plots (equipment and labour) maintenance (equipment and labour) resources tied up in data collection
Predict K from soil properties less time and expense

43. K from soil characteristics
K = 2.77 M1.14 (10-7) (12-OM) (10-3)(SS-2) (10-3) (PP-3)
K in SI units
M (% silt + % very fine sand) (100 - % clay) soil texture
OM % organic matter organic matter
SS soil structure code (USDA Soil Survey Manual) soil structure
PP USDA profile permeability class water entry
Developed by Wischmeier el al (1971)
for soils in the USA where silt + very fine sand is 70% and less but commonly used in many other places
Other equations for other soils (Volcanic) and using other properties have been developed in some countries

44. C: crop & management factor
A = R K L S C P
C = 1.0 for the “unit” plot
a bare fallow area 22 m long with a 9 % slope gradient
crop
bare
22 m
9 %
Conceptually
N  Ae.C e=1 C = —————— N  Ae e=1
Ae.C = event loss with crop and L = S = P = Ae.1 = event loss for bare fallow and L = S = P = 1.0

45. C varies geographically
C =  Ci (Ri/R) where i is a period (eg month) during a year
C depends on how rainfall erosivity varies over time
C depends on how the crop grows over time

46. C varies geographically
C =  Ci (Ri/R) where i is a period during a year
Ci values depend on above ground vegetative cover, on ground cover (trash), soil roughness (cultivation), etc – documented in technical manuals
C influenced by how well the crop grows – area not well suited, poor growth produces high C
Bare soil has high Ci. C factor highly influenced by Ri/R during cultivation for crop establishment

47. C varies geographically
C =  Ci (Ri/R) where i is a period during a year R
Avoid bare soil (high Ci) when Ri/R is high

48. P: support practice factor
A = R K L S C P
Accounts for impact of conservation practice
eg. cultivation across slope vs up/down slope P = for cultivation up/down P = for example with cultivation across
Support practices *Across slope - P varies with ridge height, furrow grade * Strip Cropping, Buffer strips, Filter strips, Subsurface drains

49. S: slope factor
A = R K L S C P
USLE: S = 65.4 sin2  sin   angle to horizontal
RUSLE: S = 10 sin  slopes <9% S= 16.8 sin  slopes 9% USLE S overpredicts erosion at high slope gradients
S = 1.0 when the slope gradient is 9 %

50. L: slope length factor L = ( / 22.13) m
A = R K L S C P
L = ( / 22.13) m
L = 1.0 when the slope is m long
USLE: m= slope >10%  m= slope <1%
RUSLE: m =  / (1+)  = ratio rill to interrill erosion
is the projected horizontal distance travelled by runoff before deposition or a channel occurs

51. Hands on RUSLE
The SOILOSS program will be used later today and can be download at anytime from
It prompts the user to go through the steps required to get a result. It requires outside knowledge of some factor values such as R.
Values for C for some crop and crop management options are calculated by the program but the options may not represent current practices. Users can setup background files to overcome such issues

52. RUSLE 2
The RUSLE does not model the effect of deposition caused by a change in slope gradient
Commonly, a factor known as the sediment delivery ratio; sediment delivered from the hillslope SDR =  erosion predicted as if no deposition occurred is used in catchment scale models.
RUSLE 2 is a hillslope model that now replaces the RUSLE in the USA. It uses physical principles to predict deposition caused by a change in slope gradient
deposit

53. RUSLE 2
22 t/ha/yr

54. Effect of Erosion on Water Quality
- an issue of concern throughout the world
In USA About 60% of the pollution in rivers comes from agriculture
In UK About 50% of the pollution in rivers comes from agriculture
In Australia Most rivers in the Murray Darling Basin are polluted to a large degree from material that comes from the land 54

55. Effect of Erosion on Water Quality
Molonglo river flows into Lake Burley Griffin

56. Effect of Erosion on Water Quality
Algae blooms are a result of nutrients that come from the land
Green: low amounts indicating early stage of a possible bloom
Amber: algae multiplying to give green tinge – water ok for recreational use only
Red: Toxic bloom conditions

57. Many catchment models use the RUSLE
Catchment scale models: Tools to model the impact of landuse on water quality
Models:
AGNPS 2000
SWAT
ANSWERS 2000
WEPP small watershed model  
Sednet Australia
USA
Europe
Many catchment models use the RUSLE

58. Catchment scale models: Tools to model the impact of landuse on water quality
AGNPS 2000, Sednet and some others include channel erosion (gullies)

59. Applying the RUSLE in 2D space
Commonly use grid cell representation of the landscape
Map overlaid with grid with e.g. spacing of 50 m
Each cell is considered to be uniform with respect to soil, vegetation, slope gradient etc
Enables soil loss caused by sheet and rill erosion to be modelled for each cell using RUSLE methodology
A1.cell = R Kcell ( Bare 22 m long 9 % slope )
Acell = A1.cell Lcell Scell Ccell Pcell 59

60. Applying the RUSLE in 2D space
channel
Representation of land use and flow directions
Generated from elevation and land cover data – Geographic Information Systems 60

61. Applying the RUSLE in 2D space1 2 3 4 5
L = (l / 22)m
A hillslope can be divided into number of lesser hillslopes
Dividing a hillslope into lesser hillslopes provides a mechanism for predicting soil loss when factors other than R vary down along a hillslope.

62. Applying the RUSLE in 2D space
Soil loss varies with flow through the cell not upslope length itself ?
Water flow through bottom cell the same in all cases

63. slope length for grid cells
Ai,j-in D
( Ai,j-in + D2)m Ai,j-inm+1 L i,j = ———————————— Dm+2 (22.13)m
Enables the USLE/RUSLE to be applied in modeling erosion in catchments 63

64. Something not in the Text Book

65. The R factor problem A = R K L S C P
R is readily mapable like all the other factors BUT is the only factor that is not affected by what is on the land surface
If the value of R is incorrect then the model output is wrong irrespective of anything else

66. The R factor problem
N N = number of events in Y years  Re Re = Event erosivity factor e= R = ———— Y Y = number of years
Re = storm energy x max 30-min rainfall intensity

67. The R factor problem
R = average annual sum of event energy (E) and the maximum 30-minute intensity (I30) Event soil loss : Ae = K (EI30)e L S Ce Pe b1
Bare fallow

68. The R factor problem Under predicts large losses
R = average annual sum of event energy (E) and the maximum 30-minute intensity (I30) Event soil loss : Ae = K (EI30)e L S Ce Pe b1
Bare fallow
Under predicts large losses
Over predicts small losses

69. The R factor problem
It is well known that a relationship exists between soil loss and runoff
BUT the USLE/RUSLE model does not consider runoff explicitly as a factor in producing soil loss

70. The R factor problem
Ae1 = Qe ce Ae1 = unit plot event loss Qe = event runoff ce = sed. concentration (soil mass per unit quantity of runoff)
USLE: ce = f (energy per unit quantity of runoff , rainfall intensity)
Analysis of plot data: ce = f (energy per unit quantity of rain , rainfall intensity)
ce = E / rainfall amount
A1e = k Qe E I30 / rainfall amount
Qe / rainfall amount = QR , the runoff ratio
Re = [QR EI30]
I30

71. The R factor problem
Re = EI30
Re = QREI30

72. The USLE-M
The USLE-M is the name given to the version of the USLE/RUSLE model that uses the QREI30 index (Kinnell and Risse, 1998)
USLE: mathematical steps A1 = R K A = A1 L S C P
USLE-M:
A1 = RUSLE-M KUSLE-M [KUSLE-M ≠ K because RUSLE-M ≠ R]
A = A1 L S C P
10 = 5 x 2
10 = 4 x 2.5
10 = 3 x 3.33

73. The R factor problem
Why does the USLE/RUSLE model not include direct consideration of runoff ?
The USLE-M works well when runoff is known or predicted well - as a general rule runoff is not easy to predict
The USLE/RUSLE model is designed to help make decisions about land management effects over the long term (~20 years) not predict short term soil loss such as event erosion or year by year variations
However, when it come to modelling the effect of landuse on water quality event soil losses are important so the USLE/RUSLE model is used to do this but in so doing the USLE/RUSLE model is being applied to do things that it wasn’t designed to do

74. Erosion Model Overview (all models not just the USLE/RUSLE)
Not all factors dealt with adequately
Familiarity with model & assumptions essential when using them
While the results may not be very accurate, they can provide a means of making useful decisions about land management in order to conserve soil and improve water quality

76. SOILOSS
SOILOSS is a computer program that runs the Revised Universal Soil Loss Equation
for various locations in New South Wales
The program is run from Explorer by double clicking on the SOILOSS Shortcut in the ALRS directory

77. Use space bar – user entry optional

78. Note instructions for data entry

79. Use “enter” to move to next screen

80. Enter zone – see climate zone map for NSW

81. R values for locations are provided using RAINER

82. Click OK to move to next screen
RAINER is run from EXPLORER by double clicking on the RAINER shortcut in the ALRS directory

83. Click on “Load” to get location selection screen and then select location from list

84. The R factor value for the location is displayed here

85. Soil erodibility is determined using the table of soils

86. Mover the cursor by the arrow keys to select the soil required – eg Chocolate

87. Slope gradient is measured in percent and will be entered in the next screen

88. After entering slope gradient enter slope length

89. Select Cultivation around the paddock

90. Select Annual Crops (standard)

91. Select a crop and press “Enter” to enter the crop for each year required

92. Select a crop and press “Enter” to enter the crop for each year required – 10 year rotation
Z to end selection prior to 10 years

93. Select tillage practice required

94. Result screen
You can use ESC to go backwards to alter data entry values and then use “enter” to strp forward to get the result