Darcy's law of permeability - explanation and formula

 Permeability is the property of a porous material which permits the seepage of water through its interconnecting voids.

The flow of water through soil may either be a laminar flow or a turbulent flow.

Darcy's law states that, "For laminar flow conditions in a saturated soil, the rate of flow or the discharge per unit time is proportional to the hydraulic gradient."

V ∝ i

V  ＝ ki

where k is co-efficient of permeability.

since, q =  AV = kiA

q = discharge per unit time

A = total cross-sectional area of soil mass

i = hydraulic gradient

V = Discharge velocity

 

 

 If a soil mass of length L and cross -sectional area A is subjected to differential head of water (∆h), the hydraulic gradient i will be ∆h/L.

And,

q = k(∆h/L)A.

When hydraulic gradient is unity,

k = V.

Thus, co-efficient of permeability is the average velocity of flow that will occur through the total cross-sectional area of soil under unit hydraulic gradient. 

Thank you.

Gracious !