Download - INFILTRATION PPT
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INFILTRATIONPRESENTED BYKARUNAKAR KEMA
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Infiltration General
Process of water penetrating from ground into soil
Factors affecting Condition of soil surface,
vegetative cover, soil properties, hydraulic conductivity, antecedent soil moisture
Four zones Saturated, transmission,
wetting, and wetting front
depth
Wetting Zone
TransmissionZone
Transition ZoneSaturation Zone
Wetting Front
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Infiltration Infiltration rate
Rate at which water enters the soil at the surface (in/hr or cm/hr)
Cumulative infiltration Accumulated depth of water infiltrating
during given time periodt
dftF0
)()(
)(tf
dttdFtf )()(
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InfiltrometersSingle Ring Double Ring
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Infiltration Methods
Horton and Phillips Infiltration models developed as approximate solutions of an exact
theory (Richard’s Equation) Green – Ampt
Infiltration model developed from an approximate theory to an exact solution
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Hortonian Infiltration Recall Richard’s
Equation Assume K and D are
constants, not a function of or z
Solve for moisture diffusion at surface
K
zD
zt
zK
zD
t
2
2
02
2
zD
t
ktcc effftf )()( 0
f0 initial infiltration rate, fc is constant rate and k is decay constant
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Hortonian Infiltration
0
0.5
1
1.5
2
2.5
3
3.5
0 0.5 1 1.5 2
Time
Infil
trat
ion
rate
, fk1
k3
k2
k1 < k2 < k3
fc
f0
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Philips Equation Recall Richard’s
Equation Assume K and D are
functions of , not z Solution
Two terms represent effects of
Suction head Gravity head
S – Sorptivity Function of soil suction
potential Found from experiment
K
zD
zt
KtSttF 2/1)(
KSttf 2/1
21)(
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Green – Ampt Infiltration
Wetted Zone
Wetting Front
Ponded WaterGround Surface
Dry Soil
0h
L
n
i
z
LLtF i )()(
dtdL
dtdFf
zh
Kz
Kf
fzhKqz
MoistureSoilInitialFront WettingtoDepth
i
L
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Green – Ampt Infiltration (Cont.)
Apply finite difference to the derivative, between Ground surface Wetting front
Kz
Kf
Wetted Zone
Wetting Front
Ground Surface
Dry Soil
L
i
z0,0 z
fLz ,
KL
KKz
KKz
Kf f
00
FL
LtF )(
1
FKf f
Kz
Kf
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1
LK
dtdL f
1
FKf f
dtdLf
Green – Ampt Infiltration (Cont.)
LtF )(
Wetted Zone
Wetting Front
Ground Surface
Dry Soil
L
i
z
LdL
dLdtK
f
f
CLLtKff
)ln(
Integrate
Evaluate the constant of integration
)ln( ffC
0@0 tL
)ln(L
LKtf
ff
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Green – Ampt Infiltration (Cont.)
)ln(L
LKtf
ff
)1ln(f
fFKtF
1
FKf f
Wetted Zone
Wetting Front
Ground Surface
Dry Soil
L
i
z
Nonlinear equation, requiring iterative solution.
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Soil Parameters Green-Ampt model requires
Hydraulic conductivity, Porosity, Wetting Front Suction Head
Soil Class Porosity Effective Porosity
Wetting Front
Suction Head
Hydraulic Conductivity
n e K (cm) (cm/h) Sand 0.437 0.417 4.95 11.78 Loam 0.463 0.434 9.89 0.34 Clay 0.475 0.385 31.63 0.03
re n
ees )1(
e
res
Effective saturation
Effective porosity
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Ponding time
Elapsed time between the time rainfall begins and the time water begins to pond on the soil surface (tp)
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Ponding Time
Up to the time of ponding, all rainfall has infiltrated (i = rainfall rate)if ptiF *
1
FKf f
1
* p
f
tiKi
)( KiiKt f
p
Potential Infiltration
Actual Infiltration
Rainfall
Accumulated Rainfall
Infiltration
Time
Time
Infil
trat
ion
rate
, fC
umul
ativ
e In
filtr
atio
n, F
i
pt
pp tiF *
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Example Silty-Loam soil, 30%
effective saturation, rainfall 5 cm/hr intensity
30.0/65.0
7.16486.0
e
e
shrcmK
cm
340.0)486.0)(3.01()1( ees
340.0*7.16
hr17.0))(65.00.5(0.5
68.565.0)(
KiKiiKt f
p
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