infiltration presentation by zulfiqar uet lhr

INFILTRATION

M.Zulfiqar Ali2016-MSGS-8

MSc Geological SciencesDepartment of Geological Engineering

University of Engineering and Technology Lahore

INFILTRATIONDefinition

Process of water penetrating from ground into soil.OR

Infiltration is the process by which water is moved from the surface to subsurface replenishing soil and recharging aquifers.

Infiltration Capacity

It is defined as the maximum amount of water per unit time that can be absorbed

under given conditions. The greater the infiltration capacity of soil, the greater

amount of water that can be infiltrated.

Percolation

• Once water enters into the soil, the process of transmission of water within the soil known as Percolation takes place.

INFILTRATION & PERCOLATION are directly interrelated.

When percolation stops infiltration also stops

Surface Entry

• If surface area is bare, this retards infiltration.

• Area covered by bushy plants or grass has better infiltration.

Bare land < Vegetated land

Factors Affecting Infiltration1. Surface Entry

2. Percolation

3. Soil Moisture

4. Climate Condition

5. Degree of Saturation

6. Human Activities

7. Porosity

8. Vegetation

9. Grain size of soil particles

10. Permeability

PercolationThe infiltration rate is bounded by the rate of Percolation.Depend on the factor,

• Soil type• Composition• Permeability

• Porosity• Stratification

• Presence of organic matter • Presence of salt


2. Percolation

3. Soil Moisture



6. Human Activities

7. Porosity

8. Vegetation


10. Permeability

Soil Moisture

• Infiltration depends on the presence of

moisture in soil .

• Second storm in succession the soil will have lesser rate of

infiltration than the first storm of the season


2. Percolation

3. Soil Moisture



6. Human Activities

7. Porosity

8. Vegetation


10. Permeability

Climate Condition

• Temperature affects the viscosity of water.


2. Percolation

3. Soil Moisture



6. Human Activities

7. Porosity

8. Vegetation


10. Permeability

Degree of Saturation

The more saturated the loose Earth materials are, the less

the infiltration inverse or indirect relationship

• The depth of the water table below the surface

varies with the amount of infiltration


2. Percolation

3. Soil Moisture



6. Human Activities

7. Porosity

8. Vegetation


10. Permeability

Human Activities

Roads, parking lots, and buildings create surfaces that are not longer permeable.

These impermeable surfaces often channel runoff.

Farming, cutting down trees and grazing animals will reduce vegetation and therefore decrease permeability.


2. Percolation

3. Soil Moisture



6. Human Activities

7. Porosity

8. Vegetation


10. Permeability

Porosity

• Porosity is the percentage of open space (pores and cracks) in a material compared to its total volume

• Generally: the greater the porosity, the greater the amount of infiltration.


2. Percolation

3. Soil Moisture



6. Human Activities

7. Porosity

8. Vegetation


10. Permeability

Vegetation• Grasses, trees and other plant

types capture falling precipitation on leaves and branches, keeping that water from being absorbed into the Earth

• If any water gets through the vegetation, the velocity of the water will be reduced and this will give the ground more time to absorb the water

• Ground without vegetation usually has high runoff and low infiltration rates


2. Percolation

3. Soil Moisture



6. Human Activities

7. Porosity

8. Vegetation


10. Permeability

SIZEWell rounded particles have a

greater porosity.

Round

particles more pore space, higher porosity,

and more infiltration

Angular particles

less pore space, less porosity, and less infiltration


2. Percolation

3. Soil Moisture



6. Human Activities

7. Porosity

8. Vegetation


10. Permeability

PermeabilityThe ability of a material to allow

fluids such as water to pass through it. Larger particles will increase permeability, because pore space is larger.

Impermeability may be due to tight packing or cementing of particles, which seals off the pores from one another.


2. Percolation

3. Soil Moisture



6. Human Activities

7. Porosity

8. Vegetation


10. Permeability

1. FIELD MEASUREMENT METHODa. Single Tube Infiltrometerb. Double Tube Infiltrometer

2. RAINFALL SIMULATOR3. RAINFALL RUNOFF ANALYSIS

Measurements of infiltration

Single Tube Infiltrometer

• Cylinder - 30 cm in Diameter & 60 cm long.

• Drive into the ground, such that 10 cm of it project above ground level.

• Water is Ponded Above the Surface

• Record Volume of Water Added with Time to Maintain a Constant Head

• Measures a Combination of Horizontal and Vertical Flow


Double Tube Infiltrometer


Outer Rings are 6 to 24 inches in Diameter (ASTM - 12 to 24 inches)

Water is Ponded Above the Surface into both rings to maintain same height.

The outer cylinder is maintained to prevent spreading of water from the inner one.

Infiltrometer Disadvantages

Single Tube Infiltrometer disadvantages

• Water spreadout immediately from the bottom which does not represent a true infiltration condition of the field.

PrecautionDrive cylinder into the ground with minimum

disturbance.

Double Tube Infiltrometer disadvantages

1. Size effect; larger diameter infiltrometers give more accurate & always lesser valve of infiltrationthan smaller diameter type.

2. Boundry effect

3. Disturbance of original soil due to driving of the rings.

The φ - index“The rate of infiltration above which the rainfall volume equals to runoff

volume”.

Infiltration indices

Effective Rainfall

Infiltration Rate

"The average value of infiltration is called infiltration index”.

P=total storm precipitation (mm) R=total surface runoff (mm)t=time

φ-index=(P-R)/t

The W – index• It is defined as average rate of infiltration which equals to the rate of

precipitation minus surface runoff & retention during time.

P=total storm precipitation (mm)

SRO =Depth of surface runoff ( mm)

DR=Total depth of surface retention

*DR=0 when heavy & longer stormt=time (hour)

w-index= (P—SRO—DR) / t

Infiltration indices