Soil Erosion Peter Kinnell

1. Soil ErosionPeter Kinnell Research area: Rainfall erosion processes and prediction http://ozemail.com.au/~pkinnell

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

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 • Wind driven saltation and creep Sahara desert

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

12. 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 Soil lost per unit area o 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 Flow

19. 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 and uplift caused by raindrops impacting flow 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) 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 impactCoarse 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 isINSIDIOUS 1 mm loss from the surface on 1 km2=1 m x 1 m x 1km channel

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

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

31. Rain Interrill Surface Runoff Rill Sheet Erosion Flow energy increasing Forms of Water Erosion on a Hillslope 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 Splash Erosion 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 CP 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 areadivided 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 CP 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 CP USLE/RUSLE used widely in the worldincluding Australia • Catchment Erosion • Urban Erosion • State of Environment Reports Implemented in NSW viaSOILOSS computer program (Dept Land & Water Conservation, NSW)

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

39. Unit Plot 22m long 9% slope bare soil 33m long 6% slope Cropped Plot  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 Works mathematically in 2 steps:1. Predict the loss from a control plot called the “unit” plot2. Use factors to adjust this to predict loss from area of interest

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) + 4.28 (10-3)(SS-2) + 3.29(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. N Ae.Ce=1C = —————— N  Ae.1e=1 Conceptually 22 m 9 % crop bare 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 Ae.C = event loss with crop and L = S = P = 1.0Ae.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 Civalues 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 slopeP = 1.0 for cultivation up/downP = 0.75 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 + 4.56 sin  + 0.0654  angle to horizontal • RUSLE:S = 10 sin  + 0.03 slopes <9%S= 16.8 sin  - 0.50 slopes 9% USLE S overpredicts erosion at high slope gradients S = 1.0 when the slope gradient is 9 %

50. L: slope length factor A = R KL S C P L = ( / 22.13) m L = 1.0 when the slope is 22.13 m long • USLE: m=0.6 slope >10% m=0.2 slope <1% • RUSLE:m =  / (1+)  = ratio rill to interrill erosion • is the projected horizontal distance travelled by runoff before deposition or a channel occurs