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Engr. Kelvin Michael A. Crystal

Department of Agricultural and Food Engineering

College of Engineering and Information Technology

Cavite State University

Indang, Cavite

• Infiltration - passage of water into the soil

surface

• Percolation – movement of water through the

soil profile

• Infiltration rate – infiltration per unit time;

expressed in volume per unit time per unit

area or depth per unit time

• Hydraulic conductivity – velocity of flow

caused by a unit gradient; flow through soils

in any direction

• Permeability – used interchangeably with

hydraulic conductivity

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• Water conservation

• Reduced soil erosion by runoff

• Irrigation (manner of application)

• Critical and maximum depth

determination in water reservoir

design

1. Soil – soil texture, soil structure; the

larger the pore size and the greater

the continuity of the pores, the greater

is the infiltration rate

• surface sealing or puddling of soil –formation of a thin compact layer on the

surface as a result of severe breakdown of

soil structure caused by the beating action

of raindrops and flow of water over the

surface

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2. Vegetation – reduces surface sealing;

has greater effect on infiltration than

soil type and texture

3. Antecedent moisture condition –

high antecedent moisture condition

causes reduction in pore space and

rate of water movement

4. Use of soil additives – chemicals that

improve the soil structure hence

increase infiltration; other chemicals

cause soil particles to swell and to

become hydrophilic hence reduce

infiltration

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Darcy equation (For one-dimensional flow of

water through a saturated homogeneous soil)

Q = k h A/L

Where: Q = flow rate (L3/T)

K = hydraulic conductivity (L/T)

h = head or potential causing flow (L)

A = cross-sectional area of flow (L2)

L = length of the flow path (L)

In case of heterogeneous soil (2 layers):

L

K = -------------------

L1/K1 + L2/K2

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Direct measurement – involves direct

measurement of water applied and water

flowing from the field

1. Double Ring Infiltrometer Method• Provides for a buffer pond to minimize the effect

of radial flow

• Cylinders are carefully driven into the soil to a

depth of about 15 cm; water is added to the

cylinder and allowed to pond carefully so as not

to puddle the soil; water levels in both cylinders

are maintained equal; recession rate of water

level in inner cylinder is recorded.

Installation of cylinders

Maintaining the water level

in the cylinders

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Other Methods

• Ponding

• Furrows

• Rainfall or sprinkler

Note: Infiltration is computed by assuming it to equal

the difference between water applied and

measured surface runoff

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The infiltration capacity at the onset of

infiltration is high. S the soil pores fill

with water as surface sealing takes

place, the rate of water intake

gradually decreases. It then normally

approaches a constant value which

may be taken as the infiltration rate of

the soil.

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Horton’s Equation

f = fc + (fo – fc) e-kt

Where: f = infiltration capacity or the maximum rate at

which soil under a given can take water

through its surface (L/T)

fc = the constant infiltration capacity as t

approaches infinity (L/T)

fo = infiltration capacity at the onset of infiltration

(L/T)

k = a positive constant for a given soil and initial

condition

t = time (T)

Sample Problem

Assuming that the Horton infiltration is

valid, determine the constant

infiltration rate if fo = 50 mm/hr, f at 10

min is 13 mm/hr, and k = 12.9. What is

the infiltration rate at 20 min?

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