10 Infiltration

7/29/2019 10 Infiltration

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INFILTRATION

AE 520


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Infiltration Lesson

Objectives Understand the factors affecting soil

water infiltration Be able to estimate infiltration rate

using the Horton Equation and theGreen-Ampt Equation

Understand the advantages of thevarious infiltration functions.


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INFILTRATE

To cause (as a liquid) to permeatesomething by penetrating its pores or interstices.

Websters Ninth New CollegiateDictionary


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INFILTRATION

The movement of water through thesoil surface into the soil profile.

After Precipitation, it is the mostimportant process controlling thewater balance on a field.

Expressed as total depth or as avelocity called the infiltration rate


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Infiltration may becontrolled by 3 types of

factors Supply Factors

Surface Factors

Profile Factors


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Infiltration Control Supply

Factors The water supply for infiltration may

be: Rainfall Surface Pond Storage Irrigation Infiltration Rate will be the minimum

of supply and Capacity


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Infiltration Control SurfaceFactors

Degree of Surface Crusting Clay content of the surface Effect of drop impact

Degree of Surface Porosity Soil texture Soil Structure Vegetation Cover Inwash of fine particles Cracks and other macropores


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EFFECT OF PROTECTIVE

COVER ON INFILTRATION


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Infiltration Control Profile

Factors Hydraulic Conductivity of the soil

layers Moisture Content of the soil layers

near the surface. Rate of internal drainage


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Measurement of Infiltration

Sprinkler Infiltrometer Rainfall

Runoff

Infiltration

Infiltration = Rainfall - Runoff


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Infiltration with supply

control

Supply rate

Time

Rate

f c


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Measurement of Infiltration

Ring Infiltrometer


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D E P T H

( F )

Infiltration with Soil Control

S l o p e = f c


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Infiltration with Soil Control

TIME

I N F I L T R A

T I O N

R A T E ( f )

D E P T H / T I M E

f dF

dT=

f c

f o


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- 0 +POTENTIAL

Z

T

p

+

m

Water Table

SoilProfile

Static

DuringInfiltration

Field Surface


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16log T

l o g

F

n

1

C

F = CT n f = CnT n-1

Kostiakovs Equation


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Hortons Equation

t

L o g

( f - f c

)

Log(f 0 - f c )

1K

( )Kt

c c ef f f f

+= 0


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Darcys Equation

dz

dKAq

dz

dKv

=

=


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0SOIL MOISTURE CONTENT

D E P T H F R O M

I N F I L T R A T I O N

S U R F A C E

ZONE OF SATURATION

TRANSITION ZONE

TRANSMISSIONZONE

WETTINGZONE

WETTING FRONT


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HOLTANS CONCEPT OFINFILTRATION

TIME

S =

T O T A L P O R O S I T Y -

W I L T I N G

P O I N T M O I S T U R E

A B O V E T H E

C O N F I N I N G L A Y E R

F m i n s lo p e = f c

F = F m i n + S - A S M

= S r

F = F m i n+ S

A C C U M U L A T E D

I N F I L T R A T I O N D E P T H


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21log ((S-F)/S)

l o g

( f - f c )

P

1A

1

Holtans EquationP

c S

F S Af f

+=


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f

1/F

K 1

K

Green-Ampt Equation

F K K f +=


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Green-Ampt Infiltration

EquationSoil Surface

Wetting Front

Wet

Dry

1

2

Lf

p

= 0

z = 0

m = f

m = i

z = Lf

p = 0

K = Constant = f = constant

= i = constant


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Equation

( )f

f if

f if

f if

LLK

dLdKV

EquationDarcytheFromL

00L0d


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Equation Both i and f are negative and i

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