Upload
zulfiqar-ali
View
60
Download
0
Embed Size (px)
Citation preview
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
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
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
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
Climate Condition
• Temperature affects the viscosity of water.
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
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
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
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.
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
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.
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
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
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
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
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
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.
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
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
Measurements of infiltration
Double Tube Infiltrometer
Measurements of infiltration
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