What makes the The Universal Soil Loss Equation Go ?

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

Universal Soil Loss Equation LC P Erosion = f (climate, soil, topography, landuse) A = R K LS C P C, PL 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 NOT mean that erosion is uniform over that area. P.I.A. Kinnell Univesity of Canberra

Universal Soil Loss Equation Erosion = f (climate, soil, topography, landuse) A = R K LS C P 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

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

A 1 = R K=10 t/ha A C =A 1 ( L S C P ) A C =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 A 1 then A C Unit Plot 22m long 9% slope Wheat Plot 33m long 6% slope P.I.A. Kinnell Univesity of Canberra

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

Event Erosivity R e = E I 30 R e = E I 30 E = Event Energy I 30 = max 30 min intensity P.I.A. Kinnell Univesity of Canberra

K: soil erodibility factor N N N= number of events  A e.1  A e.1 A e.1 = loss for C=P=LS=1 e=1 e=1 (5+ years of data) K = —————— N N C=1 : bare fallow  (EI 30 ) e  (EI 30 ) e L=1 : m e=1 e=1 S= 1 : 9% slope P=1 : cult up/down slope P.I.A. Kinnell Univesity of Canberra

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

K from soil characteristics K = 2.77 M 1.14 (10 -7 ) (12-OM) (10 -3 )(SS-2) (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 SSsoil structure code (USDA Soil Survey Manual) PPprofile permeability class (USDA Soil Survey Manual) Other equations exist for other soils (Volcanic) and using other properties P.I.A. Kinnell Univesity of Canberra

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

L: slope length factor L = ( / 22.13) m n USLE: m=0.6 slope >10%  m=0.2 slope 10%  m=0.2 slope <1% n RUSLE: m =  / (1+  )  = ratio rill to interrill erosion n  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

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

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

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

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

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

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

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

Erosion for non-uniform slopes L slope = ( /22.13) m where = distance to bottom of segment 1 2 L seg L slope = ( /22.13) m where = distance to bottom of segment (L slope x - (L 1 x 1 ) ) / 2 = L seg L for a segment increases downslope and so does erosion P.I.A. Kinnell Univesity of Canberra

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

Erosion for non-uniform slopes n Crops are irrelevant to calculation of L seg n But are relevant in the calculation of segment and hillslope erosion n A 1 = R K L 1 S 1 C 1 P 1 A 2 = R K L 2 S 2 C 2 P 2 n 1 2 ————————————— n (A 1 x 1 ) + (A 2 x 2 ) A slope = ————————————— P.I.A. Kinnell Univesity of Canberra

Potential & Real Erosion For a hillslope (A 1 x 1 ) + (A 2 x 2 ) A slope = —————————————————————— Only valid if no deposition in lower segment  RUSLE 2 does deals with deposition using transport capacity (T C ) concept  A 1 = 5 t/ha A 2 = 1t/ha both segs are 1ha in area T C2 = 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

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

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

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

S: slope factor n USLE: S = 65.4 sin 2  sin   angle to horizontal n RUSLE: S = 10 sin  slopes <9% S= 16.8 sin  slopes  9% USLE S overpredicts erosion at high slope gradients P.I.A. Kinnell Univesity of Canberra

C: crop & management factor N  A e.C e=1 C = —————— N  A e.1 e=1 N  A e.C e=1 C = —————— N  A e.1 e=1 A e.C = event loss with crop A e.1 = event loss for bare fallow N  A e.C e=1 C = —————— N  A e.C e=1 C = —————— N K  (EI 30 ) e e=1 N K  (EI 30 ) e e=1 C varies geographically P.I.A. Kinnell Univesity of Canberra

C varies geographically Australia: New South Wales has 12 Climate Zones C for Wheat Zone C C for Wheat Zone C P.I.A. Kinnell Univesity of Canberra

C varies geographically C for Wheat Zone C C for Wheat Zone C P.I.A. Kinnell Univesity of Canberra

C varies geographically C for Wheat Zone C C for Wheat Zone C x P.I.A. Kinnell Univesity of Canberra

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

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

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

P: support practice factor n Accounts for impact of conservation practice n eg. cultivation across slope vs up/down slope P=1.0 for cultivation up/down P=0.5 for cultivation across n 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

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

Peter Kinnell University of Canberra Canberra ACT 2601