Processes, Factors and Impacts

choppedspleenMechanics

Feb 22, 2014 (3 years and 10 months ago)

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Erosion and Sedimentation

Processes, Factors and Impacts
on the Environment

Issued May 2009

Level IA: Fundamentals Seminar



Education and Training Certification

Requirements for Persons Involved with Land Disturbing Activities

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OVERVIEW


Introduction of Erosion and Sedimentation (E&S)


Definitions and general stages of E&S


Basic processes and factors governing E&S


Natural erosion vs. accelerated erosion


Impacts of Erosion and Sedimentation (E&S)


Environmental impacts


Economic impacts



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EROSION

-

The process by which the
land surface is worn away by the action
of water, wind, ice and gravity

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Predevelopment

Construction

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Photograph of erosion

Water Erosion

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Types of Water Erosion

1. Splash Erosion

2. Sheet Erosion

3. Rill Erosion

4. Gully Erosion

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Raindrop

impact

on bare soil


.

Splash
Erosion

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Sheet Erosion

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Photograph of rill erosion


RILL EROSION

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Photograph of gully erosion

Gully Erosion

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Insert picture here

SPLASH

SHEET

RILL &
GULLY

STREAM &
CHANNEL

TYPES OF WATER EROSION

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Sedimentation

The process by which the eroded

material is

transported

and

deposited

by







Water



Wind



Ice



Gravity

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Photograph of sediment

SEDIMENTATION

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SEDIMENT TRANSPORT

GA stream following

1/2


of rain

June 26, 2001

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Stages in Erosion & Sedimentation


1. Detachment

2. Transport

3. Deposition

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Natural Erosion vs. Accelerated Erosion

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Natural (Normal) Erosion



Erosion

without

the

interference


of man

s activities.






The rate is generally small except


for stream channel and shore


erosion.

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Accelerated Erosion

Erosion

intensified

by human activities



Example: Farming



Example: Construction

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Expected Erosion Rates

(Tons/Acre/Year)

1. Forest Land




1

or greater

2. Farm Land



15

or greater

3. Construction Sites


100

or greater

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Impacts

of Construction Activities


1. Removal of

soil organic matter

2. Removal of

vegetation

3. Reshaping of ground

surface contours

4. Exposure of

subsoil

5. Changing the

pervious

ground surface


to

impervious

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Factors Affecting Erosion

1. Climatic (rainfall and runoff) Factors

2. Soil Factors

3. Topographic Factors

4. Vegetative Factors

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RAINDROP IMPACT & SPLASH EROSION

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The potential for soil erosion
varies during the year in GA

We have more thunderstorms

in the summer

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Rainstorm Energy
Atlanta, GA
0
2
4
6
8
10
12
14
16
18
20
January
February
March
April
May
June
July
August
September
October
November
December
Month
Pe
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Photograph of river


VOLUME AND VELOCITY OF FLOW

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Topography


SLOPE GRADIENT

SLOPE LENGTH

Gradient is expressed as number of horizontal
units per unit vertical such as 3 to 1 or 4 to 1 or
in percentage as 33 percent or 25 percent.

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Slope Gradient




4 to 1 or 4:1 means that four feet of
horizontal length are required for each
foot of vertical change in elevation




1








4



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Slope Gradient

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Soil Factors


Fine sandy & silty soils are more
erodible than clay type soil & those with
higher percentage of organic matter.


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Vegetative Factors


Absorbs raindrop impact


Reduces detachment


Roots hold soil in place


Slows water flow


Adds organic material to the soil


Reduces runoff


Increases infiltration


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Photograph of vegetation holding soil
in place

Vegetation holds

soil in place

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Photograph of vegetation slowing
water and trapping sediment

Vegetation slows the flow of water,
reducing erosion and trapping
sediment

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Photograph rate and speed of runoff

Rate and speed

of runoff

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Photograph

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Vegetation provides
organic material

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Impacts of Erosion and Sedimentation

1. Loss of

soil productivity

2. Adverse effects on other

water


resource facilities

3. Loss of

reservoir storage

capacity

4.

Flood

impacts

5
.
Recreational

impacts


6. Deterioration of

water quality


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Increased maintenance
costs for stormwater
management systems

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Decreased Recreational Value

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Biological impacts


Screens Out Sunlight = Decline in Plant Growth


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Sedimentation Disrupts The Ecosystem

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SUMMARY


Many processes and factors are involved in
erosion and sedimentation


Erosion is a natural process, but it can be
accelerated by human activities. KEEP BARE
SOIL TO AN ABSOLUTE MINIMUM!


Impacts of erosion and sedimentation can be
devastating to both the environment and the
economy

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Georgia Soil and Water
Conservation Commission

State Office

706.542.3065

Certification

706.542.1840

www.gaswcc.georgia.gov

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QUESTIONS?