Darcy's Law

Question 0

Limitation: Assumes rock is homogeneous:

Answer 0

Most rocks tend to be heterogeneous - they have different properties at different locations.

Also, permeability varies with direction.

Question 1

Three limitations:

Answer 1

Assumes rock is homogeneous.
Doesn’t account for tortousity.
Applies only to slow moving ground water.

Question 2

Limitation: Doesn’t account of tortousity:

Answer 2

Tortousity - The fact water must flow around individual grains.

Flow of water (l) is actually longer than l because fluid has to travel around grains of rock.

Question 3

Limitation: Applies only to slow moving ground water:

Answer 3

Laminar flow - streamline.

As fluid speed increases, flow becomes turbulent. This modifies the relationship between the hydraulic head and fluid speed.

Question 4

Darcy’s law is used to

Answer 4

Calculate ground water speed.

Question 5

Equation for Darcys law:

Answer 5

v = K h/l

K - hydraulic conductivity
h/l - hydraulic gradient

Question 6

The value of K depends on rock permeability and

Answer 6

The density and viscosity of the fluid.

Question 7

The larger K is, the more

Answer 7

Easily water flows through the rock.

Question 8

Equation for hydraulic conductivity (K):

Answer 8

K = pg k/v

p - fluid density
g - acceleration due to gravity

k - permeability of the rock
v - fluid viscosity

Question 9

K is large for coarse materials and

Answer 9

Small for fine materials.