• The velocity of flow and consequent discharge through a soil
  • Depends upon various factors, such as the type of soil, the arrangement of the grains, viscosity of water etc.
  • The various physical factors decide as to whether the flow will be laminar or turbulent.
  • In hydraulics, the flow in pipes is generally turbulent but in soils the flow is usually laminar.
  • We know that in laminar range of flow the velocity (V) of flow is proportional to hydraulic gradient (I).
  • This fact was confirmed by Mr. Darcy and hence later on it was called Darcy’s law of flow.
  • This law states that the rate of flow (Q) is proportional to hydraulic gradient

                             Q ∝ I

                                  = KIA

                                 \[\frac{Q}{A}= V= KI\]


  • K = Darcy’s coefficient of permeability, I being dimensionless the dimension or unit of K is that of velocity (usually cm/sec.)
  • V = Velocity of flow and
  • A = Total cross-sectional area of soil mass perpendicular to direction of flow.
  • Hence these days whole of well hydraulics is dependent upon Darcy’s law of flow through soils. This law is applicable for Laminar flows only.