Erosion Overview

SOIL EROSION

A nation that destroys its soil destroys itself

F.D.R.

President:

Soil erosion and pollution continues to be the number one problem we face

1982: 2000 report to the

SOIL EROSION

M Climate: The major- Reduced productive potential

- 85% soil erosion < 30 vegetation remains

70% vegetation remains

Part topsoil removed, rills

30-70% veget. remains

Most topsoil removed, gullies

SOIL EROSION

SOIL EROSION

0

1

2

3

4

5

6

7

8

9

10

0 120 160

(

)

Desert

Forested lands

Soil under

20 40 60 80 100 140 Annual rainfall (cm)

M

e

a

n

a

n

n

u

a

l

S

Y

M

g

/

h

a

Semiarid scrub

Subhumid grasslands

natural veg.

SOIL EROSION

Compaction/crusting

Acidification/salts

HOW MUCH ARE WE LOSING?

1/3 of worlds arable land lost since 1950

Asia/Africa/S. America: 30-40 t/ha/a

30% of US farmland abandoned (erosion, waterlogging, salinization)

1/3 of worlds arable land lost since 1950

Asia/Africa/S. America: 30-40 t/ha/a

30% of US farmland abandoned (erosion, waterlogging, salinization)


1982: 3 billion t

1992: 1.8 billion t

12 t/ha (12k lbs/ac) 8 = water 4 = wind

Mississippi River:

300 m/t/yr 10 t/sec!


T value = Tolerable erosion

equilibrium between soil gains and losses.

continuous cropping and maintain soil productivity without requiring additional management inputs.

T ranges from: 1-5 t/ac/yr

< 25 cm = 2.2 t/ha/yr > 152 cm = 11.2 t/ha/yr

Maximum soil erosion loss that is offset by the theoretical maximum rate of soil development, which will maintain an

The maximum average annual soil loss that will allow

2 11 t/ha/yr


1994: 12,000 lbs of soil lost per acre

since average person consumes 2,000 lbs per annum

6 lbs of soil lost per pound of food eaten annually!


Normally takes 500 years to build up an inch of topsoil

To grow good crops requires approximately 6 inches

3,000 years required to build up a reasonable topsoil

12,000 lbs/acre = 0.0356 inch (1/28th)

Since 1/500th of an inch is being built up naturally annually

it is being built up in nature! Soil is being depleted on the average each year 18 times faster than

ON-SITE VERSUS OFF-SITE

Soil left behind less valuable Lower OM, N and AWC Crusting Exposed B horizons

Soil left behind less valuable Lower OM, N and AWC Crusting Exposed B horizons


Much of the contaminated sediment in the U.S. was polluted years ago by such chemicals as DDT, PCBs, and mercury

Estimated that 10% of the sediment underlying our nations surface water is significantly contaminated

Sediment approx. 12 billion yards3

Contaminated sediment approx. 1.2 billion yards3

SOIL EROSION

MECHANICS OF SOIL EROSION


Rainsplash


Compaction (destroys granulation) and disruption of soil surface (detachment)


2000

0

K

E

o

f

r

a

i

n

t

o

d

e

t

a

c

h

1

K

G

(

J

)

Particle size (mm)

0.04 0.1 0.25 0.60.016


Sheetwash vs concentrated flow


Re = r/ F = / gr Reynolds number = flow turbulence

< 500 = laminar > 2000 = turbulent

Froude Number = gravity waves < 1.0 = smooth (tranquil) flow > 1.0 = rapid, supercritical (erosive) flow


Gully erosion

WIND EROSION

WIND EROSION S

e dim

ent y

iel d

( t/k

m2 / y

r) Wind erosion

Water erosion

Limestone 100,000

Sand 10,000

Alluvium 1,000

100

10

1

0 200 400 600

Mean annual precipitation (mm)

WIND EROSION

Friction (fluid)threshold

Impthre

actshold

V*t

(cm

/sec

)

50

40

30

20

10

0

0.01 0.1 1.0 10

Particle diameter (mm)

WIND EROSION

Documents

Erosion Overview