Infiltration

Question 1

What is infiltration?

Answer 1

Process of water penetrating from the ground surface into the soil.

Question 2

What is the infiltration capacity?

Answer 2

Maximum rate at which water can enter the soil.

Question 3

What happens if infiltration capacity is exceeded?

Answer 3

Flooding occurs

Question 4

How is porosity calculated?

Answer 4

n = volume of voids / total volume

Question 5

What is soil moisture content?

Answer 5

The liquid water volume in the soil

Question 6

How is soil moisture content calculated?

Answer 6

Theta = volume of liquid water / total volume

Question 7

What does soil moisture content of 0 or porosity mean?

Answer 7

0 means soil is dry
= porosity means soil is saturated

Question 8

What is the vadose zone?

Answer 8

Area between land surface and water table

Question 9

What is a property of water in the vadose zone? And what is it caused by?

Answer 9

Has a pressure head less than the atmospheric pressure (suction head).
Caused by negative pressure from capillary motion.

Question 10

What is the field capacity?

Answer 10

Amount of soil liquid moisture held in soil after excess water has drained away.

Question 11

How is field capacity measured and what is it a measure of?

Answer 11

Found after saturated soil drains for a few days. Is a measure of soil water-holding capacity.

Question 12

What is soil moisture deficit?

Answer 12

Amount of rainfall necessary to return soil to field capacity

Question 13

Define symbols in Darcy’s law equation for saturated soils

Answer 13

q = flux
K = hydraulic conductivity
dh = pressure difference
ds = distance

Question 14

What is the equation for the total head?

Answer 14

h = pressure / density x gravity + elevation

Question 15

What does Darcy’s law imply?

Answer 15

Water moves in direction of decreasing total head ie from higher energy position to lower

Question 16

What does a high K mean?

Answer 16

Water moves easier in soil

Question 17

What must be remembered about unsaturated soil’s total head equation?

Answer 17

Suction head is Negative
z is negative if measured from ground surface

Question 18

What is difference between Darcy’s law for saturated and unsaturated soils?

Answer 18

For unsaturated soils K is not constant anymore and varies with soil moisture content.

Question 19

How does a drier soil effect an unsaturated soils flux’s variables?

Answer 19

K will be smaller however suction head will be greater (more negative).

Question 20

What happens when water is ponded on a homogeneous soil?
Explain zones

Answer 20

Characteristic zones of saturation, water transmission, and soil wetting develop as the wetting front propagates downwards.

Question 21

What factors affect infiltration?

Answer 21

1. Precipitation
2. Soil Types
3. Water content in soil
4. Vegetation cover
5. Ground slope

Question 22

How does infiltration rate vary with time?

Answer 22

Slows

Question 23

Define the symbols in the infiltration rate equation

Answer 23

ft = infiltration at time t (mm/h)
fo = initial infiltration capacity
fc = final capacity
k = empirical constant (h-1)

Question 24

How can we find the total infiltration and what is the assumption required?

Answer 24

Integrate the infiltration equation with respect to time
Assumption of continuous ponding conditions

Question 25

What does the index method for calculating infiltration assume?

Answer 25

No variation in infiltration rate with time Constant infiltration capacity

Question 26

Explain how the index infiltration method

Answer 26

1. Define total runoff in mm 2. Equation SUM[(Rainfall - index)] = Runoff 3. Solve for index 4. Each (Rainfall - index) should be > 0, if not remove those contributions since they do not contribute to runoff and resolve for index 5. Repeat until condition is met 6. Index = Index_solved / time interval in which rainfall measurements are made

Question 27

What is the Green-Ampt method?

Answer 27

Model widely used in engineering models to calculate infiltration whilst considering the initial soil moisture condition

Question 28

How can infiltration be measured in the field and explain the drawbacks?

Answer 28

Infiltrometer - device used to measure the rate of water infiltration into soil ~ soil structure could be disturbed Artificial rain simulation ~ high cost

Question 29

When calculating flux, what must be remembered about equation given?

Answer 29

q = K dh/ds is mostly negative! h = total head s = distance