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What makes the The Universal Soil Loss Equation Go ?

What makes the The Universal Soil Loss Equation Go ?. Universal Soil Loss Equation. Erosion = f (climate, soil, topography, landuse) A = R K L S C P A = average annual erosion in field sized areas R = rainfall-runoff (erosivity) factor

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What makes the The Universal Soil Loss Equation Go ?

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  1. What makes the The Universal Soil Loss Equation Go ?

  2. Universal Soil Loss Equation Erosion = f (climate, soil, topography, landuse) A = R K LS CP • A = average annual erosion in field sized areas • R = rainfall-runoff (erosivity) factor • K = soil (erodibility) factor • LS = topographic factors (L re slope length S re slope gradient) • C = crop/crop management factor • P = soil conservation practice factor P.I.A. Kinnell Univesity of Canberra

  3. Universal Soil Loss Equation Erosion = f (climate, soil, topography, landuse) A = R K LS CP C, P&L are the main factors modified by land management Erosion has units of weight per unit area (t/ha) - the weight is an average value over that area but that dose NOTmean that erosion is uniform over that area. P.I.A. Kinnell Univesity of Canberra

  4. Universal Soil Loss Equation Erosion = f (climate, soil, topography, landuse) A = R K LS CP The Revised USLE (RUSLE):1997 An update of the USLE to take account of new information gained since the 1960s and 70s USLE/RUSLE used widely in the world P.I.A. Kinnell Univesity of Canberra

  5. Based on Erosion from PlotsKey issue =Unit Plot • 22 m long • 9% slope gradient • Bare fallow (no vegetation), cultivationup and down slope L = S = C = P = 1.0 P.I.A. Kinnell Univesity of Canberra

  6. Unit Plot 22m long 9% slope Wheat Plot 33m long 6% slope  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 L, S, C and P are all ratios with respect to unit plot conditions The model operates in two stages - predicts A1 then AC P.I.A. Kinnell Univesity of Canberra

  7. R: rainfall-runoff factor NN = number of events in Y years ReRe = Event erosivity factor e=1R = ————YY = number of years P.I.A. Kinnell Univesity of Canberra

  8. Event Erosivity Re = E I30 E = Event Energy I30 = max 30 min intensity P.I.A. Kinnell Univesity of Canberra

  9. K: soil erodibility factor N N= number of events  Ae.1 Ae.1 = loss for C=P=LS=1 e=1 (5+ years of data) K = —————— N C=1 : bare fallow  (EI30)eL=1 : 22.13 m e=1S= 1 : 9% slope P=1 : cult up/down slope P.I.A. Kinnell Univesity of Canberra

  10. 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 P.I.A. Kinnell Univesity of Canberra

  11. 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) Developed by Wischmeier el al (1971) for soils where silt + very fine sand is 70% and less K in SI units M (% silt + % very fine sand) (100 - % clay) - soil texture OM % organic matter SS soil structure code (USDA Soil Survey Manual) PP profile permeability class (USDA Soil Survey Manual) Other equations exist for other soils (Volcanic) and using other properties P.I.A. Kinnell Univesity of Canberra

  12. Seasonal variation in K • In RUSLE, K can be considered to vary during year in association with soil moisture • In USA wet in spring >>> dry during summercausing K to fall spring >>> summer • Not necessarily appropriate in all geographic locations P.I.A. Kinnell Univesity of Canberra

  13. L: slope length factor L = ( / 22.13) m • USLE: m=0.6 slope >10% m=0.2 slope <1% • RUSLE:m =  / (1+)  = ratio rill to interrill erosion •  depends on soil and slope % • is the projected horizontal distance travelled by runoff before deposition or a channel occurs P.I.A. Kinnell Univesity of Canberra

  14. Erosion for non-uniform slopes L applies to uniform slopes • How is it used to calculate erosion for non uniform slopes ? P.I.A. Kinnell Univesity of Canberra

  15. Erosion for non-uniform slopes Uniform slope gradient – different crops Non-uniform slope gradient – same or different crops P.I.A. Kinnell Univesity of Canberra

  16. Erosion for non-uniform slopes Can only calculate L for lengths starting at the top of the hillslope • Calculate L for  =(/22.13)m (Lslope) • Calculate L for 1 =(1/22.13)m (L1) • Multiply Lslope by  subtract L1 by 1 (X) • Divide X by 2 = L for lower segment P.I.A. Kinnell Univesity of Canberra

  17. Erosion for non-uniform slopes • Reverse of calculating the average for whole slope: (L1 x 1) + (L2 x 2) Lslope = ———————————————————————— • Calculate L for  =(/22.13)m (Lslope) • Calculate L for 1 =(1/22.13)m (L1) • Multiply Lslope by  subtract L1 by 1 (X) • Divide X by 2 = L for lower segment P.I.A. Kinnell Univesity of Canberra

  18. Erosion for non-uniform slopes • Reverse of calculating the average for whole slope:Lslope x  = (L1 x 1) + (L2 x 2) • Calculate L for  =(/22.13)m (Lslope) • Calculate L for 1 =(1/22.13)m (L1) • Multiply Lslope by  subtract L1 by 1 (X) • Divide X by 2 = L for lower segment P.I.A. Kinnell Univesity of Canberra

  19. Erosion for non-uniform slopes • Reverse of calculating the average for whole slope:Lslope x  - (L1 x 1) = (L2 x 2) • Calculate L for  =(/22.13)m (Lslope) • Calculate L for 1 =(1/22.13)m (L1) • Multiply Lslope by  subtract L1 by 1 (X) • Divide X by 2 = L for lower segment P.I.A. Kinnell Univesity of Canberra

  20. Erosion for non-uniform slopes • Reverse of calculating the average for whole slope:(Lslope x  - (L1 x 1) )/2 = L2 • Calculate L for  =(/22.13)m (Lslope) • Calculate L for 1 =(1/22.13)m (L1) • Multiply Lslope by  subtract L1 by 1 (X) • Divide X by 2 = L for lower segment P.I.A. Kinnell Univesity of Canberra

  21. Erosion for non-uniform slopes Lslope = ( /22.13)mwhere  = distance to bottom of segment(Lslope x  - (L1 x 1) )/2 = Lseg L for a segment increases downslope and so does erosion P.I.A. Kinnell Univesity of Canberra

  22. Erosion for non-uniform slopes Calculation method the same as for uniform slope gradient because m is determined only the gradient of the 2nd segment Seg 1 has different slope • Calculate L for  =(/22.13)m (Lall) • Calculate L for 1 =(1/22.13)m (L1) • Multiply Lall by  subtract L1 by 1 (X) • Divide X by 2 = L for lower segment P.I.A. Kinnell Univesity of Canberra

  23. Erosion for non-uniform slopes • Crops are irrelevant to calculation of Lseg • But are relevant in the calculation of segment and hillslope erosion • A1 = R K L1 S1 C1 P1A2 = R K L2 S2 C2 P2 • (A1 x 1) + (A2 x 2) Aslope = ————————————— P.I.A. Kinnell Univesity of Canberra

  24. Potential & Real Erosion For a hillslope (A1 x 1) + (A2 x 2) Aslope = ——————————————————————Only valid if no deposition in lower segment • RUSLE 2 does deals with deposition using transport capacity (TC) concept • A1 = 5 t/ha A2 = 1t/ha both segs are 1ha in area TC2 = 4t • Seg 1 produces 5t. 4t passes through to the bottom of seg 2.1t deposited in seg 2 and no erosion occurs in seg 2. • Hillslope has lost 4t of soil because of the control by seg 2. P.I.A. Kinnell Univesity of Canberra

  25. Potential & Real Erosion • The USLE predicts potential erosion • Deposition will result in real erosion differing from what USLE predicts • The ratio of Real Erosion to Predicted Erosionis the Delivery Ratio P.I.A. Kinnell Univesity of Canberra

  26. RUSLE 2 Wheat on 18m at 10%, 18m at 6%, 9m at 2% Slope delivery 3.8 T/A Soil loss 7.7 T/A Delivery Ratio 0.49 P.I.A. Kinnell Univesity of Canberra

  27. Sediment Delivery Ratio • Varies with catchment size • But large variation about the SDR - size relationship depending on catchment characteristics • In case of SDR from RUSLE 2 data,SDR = modelled erosion to modelled sediment deliverybased on a sediment transport model P.I.A. Kinnell Univesity of Canberra

  28. S: slope factor • 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 P.I.A. Kinnell Univesity of Canberra

  29. N Ae.Ce=1C = —————— N  Ae.1e=1Ae.C = event loss with cropAe.1 = event loss for bare fallow N Ae.Ce=1C = —————— N K  (EI30)ee=1 C varies geographically C: crop & management factor P.I.A. Kinnell Univesity of Canberra

  30. C varies geographically Australia: New South Wales has 12 Climate Zones C for WheatZone C 5 0.20 6 0.14 7 0.15 8 0.15 9 0.15 10 0.16 11 0.29 12 0.14 P.I.A. Kinnell Univesity of Canberra

  31. C varies geographically C for WheatZone C 5 0.20 6 0.14 7 0.15 8 0.15 9 0.15 10 0.16 11 0.29 12 0.14 P.I.A. Kinnell Univesity of Canberra

  32. C varies geographically C for WheatZone C 5 0.20 6 0.14 7 0.15 8 0.15 9 0.15 10 0.16 11 0.29 12 0.14 1.8x P.I.A. Kinnell Univesity of Canberra

  33. C varies geographically • Zone 11 has grater proportion of R during cultivation period • Zone 11 not good for growing wheat - less cover P.I.A. Kinnell Univesity of Canberra

  34. Calculating C • C can be calculated by weighting the short term value of C (soil loss ratio) by the proportion of R in the period  Ci Ri C = _______________ =  Ci (Ri/R) R Ci = C during period i Ri = R during period i Normally 2 week periods P.I.A. Kinnell Univesity of Canberra

  35. Calculating C • The soil loss ratio may, in turn, be calculated from subfactors accounting for prior land use, crop cover, surface (ground) cover, surface roughness • Crop cover factor includes consideration of plant structure and height P.I.A. Kinnell Univesity of Canberra

  36. P: support practice factor • Accounts for impact of conservation practice • eg. cultivation across slope vs up/down slopeP=1.0 for cultivation up/downP=0.5 for cultivation across • Support practices*Across slope - P varies with ridge height, furrow grade* Strip Cropping, Buffer strips, Filter strips, Subsurface drains P.I.A. Kinnell Univesity of Canberra

  37. Universal Soil Loss Equation Erosion = f (climate, soil, topography, landuse) A = R K LS CP Uses/Misuses • Designed for looking at average annual erosion in field sized areas • Help make management decisions • Not for predicting erosion by individual events or seasonal or year by year variations in erosion P.I.A. Kinnell Univesity of Canberra

  38. Peter Kinnell University of Canberra Canberra ACT 2601 Australia peter.kinnell@canberra.edu.au

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