Flow through soil and Darcy's Law

We can write down the equation for head as follows,


 
But inside a soil mass, V^2/2g is equal to zero. therefore,

 
Hydraulic gradient / head gradient (i) 

 
where,
i = Hydraulic gradient
delta h = head loss
L = distance parallel to the water flow

If the velocity of the ground water flow (V) is plotted against the hydraulic gradient (i) following is obtained,

Darcy's law


  
where,
V = discharge velocity
K = Coefficient of permeability (unit - m/s)
i = hydraulic gradient

we can find K by using the slope at laminar flow line (zone 1) at V vs i graph. (also there's a equation - later) 

Note: Low permeability means Head lost is more and velocity is less. 
  
Coefficient of permeability (K) 

Flow through soil depends on coefficient of permeability. And also Coefficient of permeability depends on many factors such as,

1) fluid viscosity
2) pore size distribution
3) roughness of mineral particles
4) void ration
5) degree of saturation 

where,
K = Coefficient of permeability
gamma w = unit weight of water 
neeta (n) = viscosity
K bar = absolute permeability

Please check my next blog to check the determination of K in laboratory.