Week 4 Groundwater

Question 1

What is groundwater?

Answer 1

Water present in soils and rock, originating from precipitation and infiltration

Question 2

What are the three terms used to describe the movement of groundwater?

Answer 2

• Aquifer
• Aquitard
• Aquiclude

Question 3

What is an aquifer?

Answer 3

Soil or rock deposits that permit the movement of groundwater

Question 4

What does an aquitard do?

Answer 4

Restricts the movement of groundwater

Question 5

What is an aquiclude?

Answer 5

Completely prevents the movement of groundwater

Question 6

What is the typical residence time of water in rivers?

Answer 6

Every 2 weeks

Question 7

What is artesian water?

Answer 7

Groundwater under high pressure that can rise above ground level

Question 8

What prevents artesian water from rising to the surface?

Answer 8

Overlying aquitard or aquiclude layers

Question 9

What is sub-artesian water?

Answer 9

Groundwater that rises into overlying layers but not above ground surface

Question 10

What does Bernoulli’s Energy Equation express?

Answer 10

The amount of energy in a fluid

Question 11

What is the formula for Bernoulli’s Energy Equation?

Answer 11

hT = hz + hW

Question 12

What does Darcy’s Law describe?

Answer 12

The flow of water through soils

Question 13

What is the formula for Darcy’s Law?

Answer 13

q = k i A

Question 14

What does ‘k’ represent in Darcy’s Law?

Answer 14

Coefficient of permeability

Question 15

What does ‘i’ represent in Darcy’s Law?

Answer 15

Hydraulic gradient

Question 16

What is the relationship between permeability and hydraulic gradient?

Answer 16

Permeability affects the rate of water flow through soil

Question 17

What is the typical range of permeability values for different soil types?

Answer 17

Values vary by several orders of magnitude

Question 18

What is the effect of hydraulic gradient on water seepage in gravel versus clay?

Answer 18

Gravel may result in movement within seconds, clay may take decades

Question 19

What is discharge velocity?

Answer 19

Flow rate per unit area of soil

Question 20

How is seepage velocity defined?

Answer 20

Flow of water per unit area of voids in the soil

Question 21

What is the formula to calculate seepage velocity?

Answer 21

vs = v/n

Question 22

What does ‘n’ represent in the seepage velocity formula?

Answer 22

Porosity, the ratio of volume of voids to total volume of soil

Question 23

What are the methods to measure permeability?

Answer 23

• In-situ permeability tests
• Laboratory permeability tests
• Indirect empirical methods

Question 24

What is the Hazen formula used for?

Answer 24

Estimating soil permeability from particle size analysis

Question 25

What is the formula for the Hazen formula?

Answer 25

k = C x (d10)²

Question 26

In the Hazen formula, what does d10 represent?

Answer 26

The particle size where 10% of the soil sample is smaller

Question 27

What coefficient 'C' is used for well graded soil in the Hazen formula?

Answer 27

0.01

Question 28

Calculate the permeability if 10% of a sample of well graded soil is smaller than 0.02mm.

Answer 28

k = 4 x 10⁻⁶ m/s