In pumping out test, the water is pumped out through a tube well, until a steady state is reached. The water table around the well turns into a cone of depression. The maximum depression along the centre line of the well is known as the drawdown(d).
Following assumptions are made:
- Flow follows the Darcy's law.
- Flow is laminar.
- Soil mass is isotropic and homogeneous.
- Well penetrates the aquifer to reach the impervious bed.
- Steady flow along the soil.
- Co-efficient of permeability is constant throughout.
- Natural water ground regime doesn't change.
Further, permeability can be calculated using the influence radius as given in the formula in the image below.