LESSON 4

Question 1

passage of water into the soil surface

Answer 1

Infiltration

Question 2

movement of water through the soil profile

Answer 2

Percolation

Question 3

infiltration per unit time; expressed in volume per unit time per unit area or depth per unit time

Answer 3

Infiltration rate

Question 4

velocity of flow caused by a unit gradient; flow through soils in any direction

Answer 4

Hydraulic conductivity

Question 5

used interchangeably with hydraulic conductivity

Answer 5

Permeability

Question 6

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.

Answer 6

Cumulative infiltration

Question 7

Soil Horizons/Layers

Answer 7

• Humus (O horion)
• Topsoil (A horizon)
• Subsoil (B horizon)
• Weathered rock fragments (C horizon)
• Bedrock (D horizon)

Question 8

Rich in decomposed matter

Answer 8

Humus (O horizon)

Question 9

Often rich in humus and minerals; Germinate seeds and roots growth

Answer 9

Topsoil (A horizon)

Question 10

Poor in humus, rich in minerals (Clays and mineral deposits)

Answer 10

Subsoil (B horizon)

Question 11

Little or no plant/animal life

Answer 11

Weathered rock fragments (C horizon)

Question 12

Composed of unweathered rocks

Answer 12

Bedrock (D horizon)

Question 13

Importance of Infiltration

Answer 13

• Water conservation
• Reduced soil erosion by runoff
• Irrigation
• Critical and maximum depth determination in water reservoir design

Question 14

Factors affecting Infiltration

Answer 14

1. Soil
2. Vegetation
3. Antecedent moisture condition
4. Use of Soil Additives

Question 15

Soil texture, soil structure; the larger the pore size and the greater the continuity of the pores, the greater is the infiltration rate

Answer 15

Soil

Question 16

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

Answer 16

surface sealing or puddling of soil

Question 17

Types of Soil based on structure

Answer 17

Granular
Blocky
Prismatic
Columnar
Platy
Single Grained

Question 18

Resembles cookie crumbs and usually less than 0.5 cm in diameter. Commonly found in surface horizon where roots have been growing

Answer 18

Granular

Question 19

Irregular blocks that are usually 1.5 - 5.0 cm in diameter

Answer 19

Blocky

Question 20

Vertical columns of soil that might be a number of cm long. Usually found in lower horizons

Answer 20

Prismatic

Question 21

Vertical columns of soil that have a “soil cap” at the top. Found in soils of arid climates

Answer 21

Columnar

Question 22

Thin, flat plates of soil that lie horizontally. Usually found in compacted soil

Answer 22

Platy

Question 23

Soil is broken into individual particles that do not stick together. Always accompanies a loose consistence. Commonly found in sandy soils

Answer 23

Single grained

Question 24

Infiltration rates of different soil structures

Answer 24

Rapid - Single-grain, Granular

Moderate - Blocky, Prismatic

Slow - Platy, Massive

Question 25

Reduces surface sealing; has greater effect on infiltration than soil type and texture

Answer 25

Vegetation

Question 26

causes reduction in pore space and rate of water movement

Answer 26

Antecedent moisture condition

Question 27

chemicals that improve the soil structure hence increase infiltration; other chemicals cause soil particles to swell and to become hydrophilic hence reduce infiltration

Answer 27

. Use of soil additives

Question 28

Methods of measurement of infiltration rate

Answer 28

Double Ring Infiltrometer Method Ponding Furrows Rainfall/sprinkler

Question 29

involves direct measurement of water applied and water flowing from the field

Answer 29

Direct Measurement

Question 30

- 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.

Answer 30

Double Ring Infiltrometer Method

Question 31

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.

Answer 31

High ; decreases

Question 32

RATIONAL METHODS OF PREDICTING INFILTRATION

Answer 32

- Lewis-Kostiakov Equation - Philip’s Equation - Green – Ampt Equation - Horton’s Equation