soil erosion and mechanics.ppt

8/9/2019 Soil Erosion and Mechanics.ppt

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Soil Erosion


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What is soil erosion?

1. The wearing away of the land surface by

running water, wind, ice or other geologicalagents, including such processes as

gravitational creep.

. !etach"ent and "ove"ent of soil or roc#frag"ents by water, wind, ice or gravity.


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!ifferent types of water

erosion$ %ccelerated erosion

&eological or natural erosion

!onga or gully erosion

'or"al erosion

(ill erosion

Sheet erosion Splash erosion

Tunnel erosion or piping


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Effects of erosion$

)n site* +oss of fertile topsoil

Selective re"oval of organic "atter and fine "aterial

+oss of seeds and seedlings

hange in slope topography -unsafe conditions, "ore

difficult re"ediation, high epense/

hange in soil characteristics li#e per"eability,

infiltration rate, etc.

)ff site* 0uildup of sedi"ent and water elsewhere in the syste"


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The "echanics of soil

erosion$ !etach"ent

Transportation

!eposition


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The effects of raindrops*

!etach soil !estroy granulation

an lead to crusting

Transport of particles in so"e cases


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Transport (ainsplash

(unning water'0 nfiltration capacity

Sheetwash &ully erosion

!eposition an occur over long distances or short

distances

%"ount of soil delivered to strea" divided bythe a"ount eroded 2 deliver ratio


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3rediction and "odelling of

soil erosion$Why would we want to predict soil erosion?

)pti"al resource "anage"ent Evaluation of conse4uences of different land use

o"pliance with environ"ental re4uire"ents

!evelop"ent of sedi"ent control plans

-particularly for construction pro5ects/

3rediction of da" infiltration rates$


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What do we need to understand

before we can predict erosion?What factors affect soils6 susceptibility to

erosion? Erosivity of erosion agents. Erodibility of soils. +ength of slope.

&radient of slope. +and cover and "anage"ent.

'0 vegetation, plant residues, soil tillage

Erosion control practices.


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Erosivity$

Total rainfall

ntensity and seasonal distribution of the rain

Why is intensity i"portant? ntense rains have large drop si7e

8igher rate of rainfall 2 "ore runoff


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Erodibility$

ndicates a soil6s inherent susceptibility to erosion nfiltration capacity

Structural stability

3roperties that tend to result in high erodibility 8igh fine sand and silt content

Epansive clay "inerals

"pervious soil layers

0loc#y, platy or "assive soil structure


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3roperties that lead to low erodibility8igh organic "atter content

'onepansive clays

Strong granular structure


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So"e i"portant principles in

erosion control$


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So"e i"portant principles in

erosion control$ 9eeping disturbed soil covered

ontrolling runoff

Trapping sedi"ent

%ltering soil properties -"ore difficult/

soil erosion and mechanics.ppt

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