LESSON 4 Flashcards
passage of water into the soil surface
Infiltration
movement of water through the soil profile
Percolation
infiltration per unit time; expressed in volume per unit time per unit area or depth per unit time
Infiltration rate
velocity of flow caused by a unit gradient; flow through soils in any direction
Hydraulic conductivity
used interchangeably with hydraulic conductivity
Permeability
The summation of the depth of water absorbed by a soil in a specified elapsed time in reference to the time of initial water application.
Cumulative infiltration
Soil Horizons/Layers
- Humus (O horion)
- Topsoil (A horizon)
- Subsoil (B horizon)
- Weathered rock fragments (C horizon)
- Bedrock (D horizon)
Rich in decomposed matter
Humus (O horizon)
Often rich in humus and minerals; Germinate seeds and roots growth
Topsoil (A horizon)
Poor in humus, rich in minerals (Clays and mineral deposits)
Subsoil (B horizon)
Little or no plant/animal life
Weathered rock fragments (C horizon)
Composed of unweathered rocks
Bedrock (D horizon)
Importance of Infiltration
- Water conservation
- Reduced soil erosion by runoff
- Irrigation
- Critical and maximum depth determination in water reservoir design
Factors affecting Infiltration
- Soil
- Vegetation
- Antecedent moisture condition
- Use of Soil Additives
Soil texture, soil structure; the larger the pore size and the greater the continuity of the pores, the greater is the infiltration rate
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
surface sealing or puddling of soil
Types of Soil based on structure
Granular
Blocky
Prismatic
Columnar
Platy
Single Grained
Resembles cookie crumbs and usually less than 0.5 cm in diameter. Commonly found in surface horizon where roots have been growing
Granular
Irregular blocks that are usually 1.5 - 5.0 cm in diameter
Blocky
Vertical columns of soil that might be a number of cm long. Usually found in lower horizons
Prismatic
Vertical columns of soil that have a “soil cap” at the top. Found in soils of arid climates
Columnar
Thin, flat plates of soil that lie horizontally. Usually found in compacted soil
Platy
Soil is broken into individual particles that do not stick together. Always accompanies a loose consistence. Commonly found in sandy soils
Single grained
Infiltration rates of different soil structures
Rapid - Single-grain, Granular
Moderate - Blocky, Prismatic
Slow - Platy, Massive
Reduces surface sealing; has greater effect on infiltration than soil type and texture
Vegetation
causes reduction in pore space and rate of water movement
Antecedent moisture condition
chemicals that improve the soil structure hence increase infiltration; other chemicals cause soil particles to swell and to become hydrophilic hence reduce infiltration
. Use of soil additives
Methods of measurement of infiltration rate
Double Ring Infiltrometer Method
Ponding
Furrows
Rainfall/sprinkler
involves direct measurement of water applied and water flowing from the field
Direct Measurement
- 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.
Double Ring Infiltrometer Method
The infiltration capacity at the onset of infiltration is _____________. As the soil pores fill with water as surface sealing takes place, the rate of water intake gradually ________________. It then normally approaches a constant value which may be taken as the infiltration rate of the soil.
High ; decreases
RATIONAL METHODS OF PREDICTING INFILTRATION
- Lewis-Kostiakov Equation
- Philip’s Equation
- Green – Ampt Equation
- Horton’s Equation
