soil loss estimation

INVOLVE THE PROCESSES OF DETACHMENT, TRANSPORT AND DEPOSITION OF SOIL PARTICLES BY WATER

MAJOR FORCES OF SOIL EROSION: IMPACTS OF RAINDROPS AND FROM WATER FLOWING OVER THE LAND SURFACE

Erosion Sediment

http://www.uwsp.edu/geo/faculty/ritter/images/lithosphere/mass_wasting_erosion/landslide_La_Conchita_CA_USGS_slide21.jpg

ERODIBILITY soil which is susceptible to erosion

A soil ability to withstand rainsplash depend partially upon its texture characteristic

Sand and silt more vulnerable to erode

EROSIVITYpotential energy (wind,rainfall) to cause erosion

6

To guide in making methodical decisions in soil conservation planning.

The equation enables the planner to predict the average rate of erosion for various combinations of management techniques on a site.

Soil loss estimation is a set of management strategies for prevention of soil being eroded from the earth‟s surface or becoming chemically altered by overuse, acidification, salinization or other chemical soil contamination

http://en.wikipedia.org/wiki/Soil

http://en.wikipedia.org/wiki/Erosion

http://en.wikipedia.org/wiki/Acid

http://en.wikipedia.org/wiki/Salinization

http://en.wikipedia.org/wiki/Soil_contamination

http://en.wikipedia.org/wiki/Soil_contamination

In civil construction projects, soil loss estimation is used for the following activities :

Assessment of the potential erosion hazard associated with the given project

Identification of high risk construction projects during the planning and/or design phase

The sizing of the “sediment storage volume” of Sediment Basins

Assessment of the relative performance of alternative soil conservation practices, Erosion and Sediment Control procedures or construction programs

7

APPLICATION OF SOIL LOSS

IN CIVIL CONSTRUCTION

The amount of eroded soil that is delivered to a point in the watershed that is remote from the origin of the detached soil particles.

8

In a watershed, soil loss includes the erosion from slopes, channels, and mass wasting, minus the sediment that is deposited after it is eroded but before it reaches the point of interest.

9

Separate Diameter (mm) Comparison Feel

Very coarse sand 2.00-1.00 36" Grains easily seen, sharp, gritty

Coarse sand 1.00-0.50 18"

Medium sand 0.50-0.25 9"

Fine sand 0.25-0.10 4 1/2" Gritty, each grain barely visible

Very fine sand 0.10-0.05 1 3/4"

Silt 0.05-0.002 7/16" Grains invisible to eye, silky to touch

Clay <0.002 1/32" Sticky when wet, dry pellets hard, harsh

10

SOIL SEPARATES

11

SOIL PYSICAL PROPERTIES

RELATIVE SIZES OF SOIL SEPARATES

12

SOIL PYSICAL PROPERTIES

SOIL TEXTURE

„UNIVERSAL‟ SOIL LOSS EQUATION (USLE)

REVISED USLE

MODIFIED USLE

13

14

UNIVERSAL SOIL LOSS EQUATION(USLE)

Compute average annual soil loss caused by sheet and rill

erosion

Applies to overland flow on slopes

Computes sediment yield from slope

Computes deposition on slope

Computes soil particles

15

Tool for conservation planning

Assess BMP effectiveness

Assess performance goals

Achieve sustainable use of soil resource

Prevent excessive sedimentation

Prevent degradation of water quality

Not for water quality enforcement

16

Cropland

Construction sites

Disturbed forestland

Rangelands

Surface mined land

Reclaimed land

Landfills

17

Easy to understand and use

Minimal resources

Input values readily available

Independent of land use

Vast experience (50 years)

18

19

Model of USLE Equation

A

Topography

Erosion

Control

P

Rainfall

RLS

Crop

Soil

Sun

K

C

A = Average annual Soil Erosion Loss (t/ha/yr)

R = Rainfall Erosivity Factor (MJ.mm/(ha.hr.yr))

K = Soil Erodibility Factor (t.ha.hr/(ha.MJ.mm))

L = Slope Length Factor

S = Slope Steepness Factor

C = Cover and Management Factor

P = Conservation Practice Factor

A = RKLSCP

20

The rainfall factor R accounts for differences in rainfall intensity-duration-frequency

for different location, i.e. the average number of erosion-index units in a year of rain

The erosion potential of a rainstorm is directly proportional value of two rainfall

characteristic:

i) total kinetic energy of the storm (E)

ii) Its maximum 30 minutes intensity (I30)

The erosivity factor as given by FRIM (1999)

R = (EI 30 )/ 170.2

E = 9.28P – 8838.15

Where I30 = the maximum 30-minute rainfall intensity

(mm/hr) for the storm of required ARI

E = annual erosivity (J/m2)

P = annual rainfall (mm)

21

The soil-erodibility factor, K is the rate of soil loss per unit of

rainfall erosivity factor R or EI30 for a specified soil.

It is measured on a unit plot, which is a 22.1m length of uniform

9% slope continuously in clean tilled fallow.

The K factor has unit of mass per area per erosivity unit.

The soil-erodibility are affected are

i) physical features of the soil

ii) topographic features

iii) land management

22

The K factor can also be determined using Nomograph.

The nomograph has been derived from the following

equation (Tew,1999)

100K = 1.0M 1.14(10-4)(12-a) + 4.5(b-3) + 8.0(c-2)

Where;

M = (% silt + % very fine sand) x (100% clay)

a = % organic matter

b = soil structure code

c = permeability class

23

24

Energy Circuit Model of USLE

25

Malaysia Soil Erodibility Nomograph for Calculation of Soil Erodibility

Factor (K) (Tew,1999)

The effects of slope length and steepness are usually combined into one

single factor, namely LS factor, which can be computed by

LS = (λ/22.13)m(0.065 + 0.046S + 0.0065S2)

where

λ = slope length (m)

S = slope gradient in percent

m = 0.2 for S<1%, 0.3 for 1%<S<3%, 0.4 for 3%<S<5%,

0.5 for 5%<S<12% and 0.6 for S>12%

Alternatively, the nomograph in FRIM(1999) can be used

26

27

Runoff begins

Deposition begins

Slope-Length selection

28

Combine Slope Length-Steepness Factor, LS (Wischmeier & Smith))

C Cover factor = The ratio of soil loss from an area with specific cover compared to bare soil conditions.

P Management practice factor = The ratio of soil loss for a given surface condition compared to a hill where plowing is perpendicular to contours.

Use C factor & P factor charts29

The cover management factor is the ratio of soil loss from a

field with given cropping and management practices to the

loss from the fallow conditions used to evaluate the K factor.

The factor C also depends upon a period of time within which

weather effects would have varying influences.

30

The conservation practice factor, P is the ratio of soil loss with

one of these practices to the loss with straight-row farming up

and down the slope.

The factor P of USLE is a dimensionless supporting erosion

control, which has a specific value for slope groups from 1.1

to 24% as shown in Table 4

31

32

Land Cover CP factor

Water body 0.000

Bareland (mining areas, newly cleared land, etc) 1.000

Horticultural 0.250

Permanent Cropland 0.150

Cropland 0.200

Rangeland 0.229

Grassland 0.015

Forest 0.010

Swamps 0.001

Residential 0.003

Impervious 0.005

Commercial 0.008

Construction 1.000

Cropping and Management Practices factor (CP)

Slope (%) Conservation Practice (P) Values

Contouring Terracing (Strip

contour-

cropping)

1.1 – 2.0 0.60 0.30

2.1 – 7.0 0.50 0.25

7.1 – 12.0 0.60 0.30

12.1 – 18.0 0.80 0.40

18.1 – 24.0 0.90 0.45

33

Table 4 : Conservation Practice Factor (P) for

Contouring and Terracing

The USLE predicts the average soil loss.

The USLE considers only sheet and rill erosion nor gully

erosion.

The USLE does not calculate sediment deposition.

34

Step 1 : Determine the R factor

Step 2 :Determine the K value from the nomograph i.e based on the particle size

distribution analysis of the soil sample.

Step 3 :Divide the area into sub-area of uniform slope gradient and length (LS).

Step 4 :Choose appropriate values C to represent the seasonal average of the

effect of mulch and vegetation.

Step 5 : Use recommended values of P based on the erosion control practice

being considered.

Step 6 : Evaluate the product of the five factors to obtain the soil loss per

unit area.

Step 7 : Multiply the soil loss per unit area by the total basin area to obtain

the total sediment volume.

35

36

REVISED UNIVERSAL SOIL LOSS EQUATION(RUSLE)

RUSLE is commonly used to predict long-time average soil loss rates.

RUSLE considered best estimates based on long-term average rainfall records.

RUSLE are not absolute values, nor an estimate of soil losses within a given year or given time period.

RUSLE does not attempt to predict sediment deposition rates or sediment transportation down-slope of sediment control measures.

37

Revised Universal Soil Loss

Equation (RUSLE)

Similar as RUSLE however, three of the five parameters have been updated.

The updated parameters are :

Rainfall factor, R

Soil erodibility factor, K

Topographic factor, LS

The R factor derived from probability statistic by analyzing additional rainfall

records of individual storm.

The K factor modified to take into account for seasonal changes.

38


Equation (RUSLE)

R = 164.74 (1.1177)s S0.64444

Where;

S = 2 year ARI, 6hour rainfall event (mm)

39

Rainfall Erosivity Factor, R

No. Soil Layers K Factor Texture Hydrological Soil Group

1 Beriah a 0.054 Clay D

b 0.057 Clay D

c 0.057 Clay D

2 Bukit Temiang a 0.042 Sandy clay C-D

b 0.035 Clay loam C

c 0.035 Clay loam C

3 Chempaka a 0.049 Sandy clay loam C

b 0.045 Sandy clay loam C

c 0.045 Sandy clay loam C

4 Clay Over Organic a 0.048 Clay D

b 0.048 Clay D

c 0.048 Clay D

5 Holyrood a 0.048 Sandy clay loam C

b 0.048 Sandy clay loam C

c 0.048 Sandy clay loam C

6 Organic Clay a 0.046 Clay D

b 0.042 Clay D

c 0.042 Sandy clay C-D 40

Soil Erodibility Factor, K

Accounts for the effect of topography on erosion.

The L factor represents the slope length, and the S factor represents the slope steepness.

41

42


Equation (RUSLE) Schematic

slope failure

Slope Length and Steepness Factor, LS

43


Deposition Beginning and

Ending on a Slope

SLOPE

M

Slope Length, in meters (λ)

s (%) S (◦) S (rad) 1.0 3.0 5.0 10.0 15.0 20.0 30.0 50.0 75.0 100.0

0.20 0.12 0.002 0.200 0.040 0.050 0.055 0.064 0.069 0.073 0.079 0.088 0.095 0.101

0.50 0.29 0.005 0.200 0.048 0.060 0.067 0.076 0.083 0.088 0.095 0.105 0.114 0.121

1.00 0.57 0.100 0.300 0.046 0.065 0.075 0.093 0.105 0.114 0.129 0.15 0.169 0.185

2.00 1.15 0.200 0.300 0.072 0.100 0.117 0.144 0.163 0.178 0.200 0.234 0.264 0.288

3.00 1.72 0.030 0.400 0.076 0.118 0.144 0.190 0.224 0.251 0.295 0.362 0.426 0.478

4.00 2.29 0.040 0.400 0.102 0.159 0.195 0.257 0.302 0.339 0.399 0.489 0.575 0.645

5.00 2.86 0.050 0.500 0.097 0.168 0.217 0.308 0.377 0.435 0.533 0.688 0.842 0.973

6.00 3.43 0.060 0.500 0.122 0.212 0.273 0.387 0.473 0.547 0.669 0.864 1.059 1.222

8.00 4.57 0.080 0.500 0.180 0.313 0.404 0.571 0.699 0.807 0.989 1.276 1.563 1.805

9.00 5.14 0.090 0.500 0.214 0.370 0.478 0.676 0.828 0.956 1.171 1.511 1.851 2.137

12.00 6.84 0.119 0.600 0.242 0.468 0.636 0.964 1.230 1.462 1.864 2.533 3.23 3.839

14.00 7.97 0.139 0.600 0.309 0.598 0.812 1.231 1.570 1.866 2.380 3.234 4.124 4.902

16.00 9.09 0.159 0.600 0.384 0.743 1.010 1.530 1.952 2.320 2.959 4.02 5.127 6.093

20.00 11.31 0.197 0.600 0.559 1.081 1.469 2.226 2.839 3.374 4.303 5.846 7.457 8.861

25.00 14.04 0.245 0.600 0.823 1.591 2.162 3.277 4.179 4.303 6.334 8.606 10.977 13.045

30.00 16.70 0.291 0.600 1.138 2.199 2.988 4.529 5.777 8.756 8.756 11.896 15.173 18.032

40.00 21.80 0.381 0.600 1.919 3.710 5.041 7.640 9.744 14.769 14.769 20.067 25.593 30.415

44


LS factor calculated using MSMA approach

The factor that involves the most professional judgement. Length

determinations made by users can vary greatly for the same site.

To apply RUSLE, erosion can be calculated for several different

sub-areas on a site and the results averaged according to the area

represented by each slope length.

Sometimes a particular position on the landscape is chosen as the

location for the slope length to represent the whole site.

45


The LS factor uses different eqn. than used in USLE. The eqn. has

been developed to reflect rangeland, row crop, construction sites and

thawing soil conditions.

The C and P factor represents a combined effect of interrelated cover

and management variables.

RUSLE brings in a mixture of empirical and process-based erosion

technology to provide a better measure of the effect land management

on erosion rates.

46

Revised Universal Soil Loss Equation (RUSLE)

47

Crop Management, C Factor

48

Erosion Control Practice, C Factor

49

Erosion Control Practice, P Factor

The limitations of RUSLE can be summarized as follows:

RUSLE provides soil-loss estimates rather than absolute soil-loss data.

The soil-loss estimates are long-term average rates rather than precipitation-event

specific estimates.

There are hill slope-length and gradient limits for which the component RUSLE

equations have been verified.

RUSLE does not produce watershed-scale sediment yields, and it is inappropriate

to input average watershed values for the computation of the RUSLE factors.

50


Equation (RUSLE)

51

MODIFIED UNIVERSAL SOIL LOSS EQUATION(MUSLE)

The Modified USLE is used to calculate sediment yield of a basin

as a result of a specific storm event.

T = Ψ2 (V x QP) 0.56 x K x LS x C x P

where

T = sediment yield per storm event (tones or tons)

Ψ2 = 89.6 for SI units and 95.0 for English units

V = Volume of runoff (cubic meters or acre-feet)

QP = Peak flow ( m3/s or ft3/s )

K, LS, C and P are USLE Parameters

52

Modified Universal Soil Loss

Equation (MUSLE)

53

EXAMPLES

54

1. Catchment area :

Total Area for Plot 1 & 2 = 38500 + 47750

= 86250 m2

= 8.62 ha

55

Soil Erodibility Factor (K factor)

Malaysia

1.How to determine K

56

Summary of Laboratory Test Result (Deng Seng, 2004)Malaysia


57

Hand

Auger No.

Depth

(m)

% Silt &

Very Fine

Sand

% Sand

(0.06 – 2.0

mm)

%

Organic

Matter

Soil Structure

Classification

Permeability

Classification

K Factor Average

K factor

HA1 0.5

1.0

41.7

37.5

43.1

27.1

0.1

0.1

3

4

3

2

0.12

0.05

0.09

HA2 0.5

1.0

34.5

23.4

53.1

56.0

0.1

0.1

3

3

3

3

0.09

0.08

0.09

HA3 0.5

1.0

36.7

50.1

54.3

38.8

0.1

0.1

3

3

3

3

0.11

0.20

0.16

HA4 0.5

1.0

35.1

36.4

50.8

52.9

0.1

0.1

3

3

3

3

0.09

0.10

0.10

HA5 0.5

1.0

37.7

42.2

49.1

38.5

0.1

0.1

3

3

3

3

0.10

0.10

0.10

HA6 0.5

1.0

83.8

86.0

16.0

13.9

0.1

0.1

3

2

4

4

0.44

0.45

0.45

Summary of Laboratory Factor Analysis Result Summary


58


Malaysian Soil Series

59


60


61

1. Calculation of LS factor using equation as follow

LS = (λ/22.13)m (0.065 + 0.0046S + 0.0065S2)

where

S = 10.0%

m = 0.50 for 5%<S<12%

λ = 60.0m

Hence, the LS factor;

LS = 1.2531

62

Assuming the condition at site is bareland (newly cleared area)

CP = 1.00

63

Storm Event

The design storm event for Plot 1 & Plot 2 (3month ARI)

Plot 1 catchment area = 38500 m2

Plot 2 catchment area = 47750m2

Overland flow length = 500m

Duration of storm = 16.2 min

Intensity of design storm = 104.8 mm/hr

Runoff coefficient = 0.74

Sub-catchment (m2)

Volume(m3)

Peakflow(m3/s)

Kfactor

LS factor

CPfactor

SedimentYield (tones)

38500 806.153 0.8294 0.09 1.2531 1.00 386.04

47750 999.8392 1.0286 0.09 1.2531 1.00 491.31

64

Total sediment yield for Plot 1 and Plot 2 = 877.35 tonnes per storm

event

4. Calculation of sediment yield using MUSLE

65

Calculation of rainfall factor using the following methods:

i) Using the following empirical study in Indonesia by Bols (1978)

R1 = 2.5 P2

100 x (0.073P + 0.73)

where

R1 = Rainfall Erosivity Factor (MJ.mm/ha.hr.yr)

P = Annual Rainfall (mm)

ii) Relationship given by FRIM (1999)

R2 = (EI 30) .

170.2

E = 9.28P – 8838.15

where E = Rainfall Erosivity factor (J/m2)

P = Annual Rainfall (mm)

I30 = The maximum 30-minutes rainfall intensity with design ARI

(mm/hr)

No. Station

Name

Station

No.

Source Average Annual

Rainfall (mm)

I 30 R factor

(i)

R factor

(ii)

1 Ladang The Blue

Valley

9001 TNB 2332.3 71.3 795.323 5364.51

2 Pejabat TNB Kg

Raja

9002 TNB 2226.6 71.3 759.125 4953.59

3 Alur Masuk

Telom

9003 TNB 1993.3 71.3 679.229 4046.62

Sub-catchment (m2)

R factor

(i)

R factor

(ii)

K

Factor

LS

Factor

CP

Factor

Soil

Loss (i)

(tones)

Soil

Loss (ii)

(tones)

38500 744.56 4788.24 0.09 1.2531 1.00 83.97 540.013

47750 744.56 4788.24 0.09 1.2531 1.00 83.97 540.013

66

3 rainfall stations with their average annual rainfall

6. Calculation of soil loss using USLE

Total soil loss for Plot 1 and Plot 2 (Bols eqn.) = 167.94 tonnes/ha.yr

Total soil loss for Plot 1 and Plot 2 (FRIM eqn.) = 1,080.026 tonnes/ha.yr

67

Storm Event

The design storm event for Plot 1 & Plot 2 (3month ARI)

Plot 1 catchment area = 38500 m2

Plot 2 catchment area = 47750m2

Overland flow length = 500m


Runoff coefficient = 0.74

Sub-catchment (m2)

Volume(m3)

Peakflow(m3/s)

Kfactor

LS factor

CPfactor

SedimentYield (tones)

38500 806.153 0.8294 0.09 1.2531 1.00 386.04

47750 999.8392 1.0286 0.09 1.2531 1.00 491.31

68

Total sediment yield for Plot 1 and Plot 2 = 877.35 tonnes per storm

event

7. Calculation of sediment yield using MUSLE

69

USLE

Total soil loss for Plot 1 and Plot 2 (Bols eqn.) =

269.74 tonnes/ha.yr

Total soil loss for Plot 1 and Plot 2 (FRIM eqn.)

= 1,667.48 tonnes/ha.yr

MODIFIED USLE

Total sediment yield for Plot 1 and Plot 2

= 1354.58 tonnes per storm event

70

ASSIGNMENT

The exercise given is to enable the participants to predict soil loss using

USLE and the sediment yield using MUSLE equation.

1.Given soil properties. Calculate K factor using nomograph.

Catchment Depth % silt

& very

fine

sand

% sand %

organic

matter

Soil structure

Classification

Permeability

Classification

K

factor

Average

K

A 0.1 36.4 54.3 0.1 3 3

0.5 50.1 38.8 0.1 3 3

71

2. Calculate LS factor.

Given: S = 15%

λ = 70 m

3. Calculate R factor using FRIM equation;

Site: Sibu

(i)AR1 2 year ; a= 3.0878, b = 1.6430, c = -0.4472, d = 0.0262

(ii) P = 3000mm

Find;

(i)2I30

(ii)R

72

4. Calculate soil loss;

Given: CP = 1.00

A = RKLSCP

5. Calculation of sediment yield using MUSLE eqn.

Use K,LS,CP from previous USLE exercise.

Given:

Catchment area A = 40,000m2

Duration of storm = 30 min


Runoff coeff. = 0.82

73

The exercise given is to enable the participants to predict soil loss using USLE

and the sediment yield using MUSLE equation.

1.Given soil properties. Calculate K factor using nomograph.

Catchment Depth % silt

& very

fine

sand

% sand %

organic

matter

Soil structure

Classification

Permeability

Classification

K

factor

Average

K

A 0.1 36.4 54.3 0.1 3 3 0.1000 0.1475

0.5 50.1 38.8 0.1 3 3 0.1950

74

2. Calculate LS factor.

Given: S = 15%

therefore choose m = 0.6

λ = 70 m

LS = ( λ / 22.13) m (0.065 + 0.046S + 0.0065S2)

= (70 / 22.13)0.6 (0.065 + 0.046[15]) + 0.0065(15) 2)

= (1.9955)(0.065 + 0.69 + 1.4625)

= (1.9955).(2.2175)

= 4.425

3. Calculate R factor using FRIM equation ;

Site: Sibu

(i) ARI 2 year ; a= 3.0879, b = 1.6430, c = -0.4472, d = 0.0262

(ii) P = 3000mm

Find;

(i) 2I30 = 93.088 mm/hr ; (where ln 2I30 = 4.534)

(ii) R = EI30/170.2 ; where E = 9.28P – 8838.15

= 9.28(3000) – 8838.15

= 19,001.85 J/m2

therefore R = (19,001.85 x 93.088)/170.2

= 10,392.74 MJ.mm/ha.hr.yr

75

4. Calculate soil loss;

Given: CP = 1.00

A = RKLSCP

= 10,392.74 x 0.1475 x 4.425 x 1.0

= 6,783.21 tonne/ha/yr

5. Calculation of sediment yield using MUSLE eqn.

Use K,LS,CP from previous USLE exercise.

Given:

Catchment area A = 40,000m2 = 4 ha

Duration of storm = 30 min


Runoff coeff. = 0.82

T = Ψ2 (V x QP) 0.56 x K x LS x C x P ; where Ψ = psi

= 89.6 for S.I units

QP = CIA/360 = (0.82 x 93.088 x 4) / 360

= 0.848 m3/sec

Volume, V = Q x t = 0.848 x (30 x 60) = 1,526.4 m3

As such ,

T = 89.6 x (1,526.4 x 0.848) 0.56 x 0.1475 x 4.425 x 1.0

= 89.6 x 55.30 x 0.1475 x 4.425 x 1.0

= 3,233.99 tonnes 76

Density of sediment, ρ = 2.6 tons/m3

ρ = Weight / Volume

Volume sediment = 3,233.99 / 2.6= 1,243.84 m3

Assumption: Cost for excavation and transportation of sediment at site;1 m3 = RM 10.00

Therefore cost for excavation + transportation = 1,243.84 m3 x RM 10.00= RM 12,438.42 per rainfall event

77

soil loss estimation

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