The equation hW=h – Z, can be used to plot pressure net representing lines of equal water pressure without the saturated soil mass since all the three quantities in the equation can be expressed a the percentage of total hydraulic head H.

The seepage medium is replaced by an electric conductor consisting of water with some salt or dilutes hydrochloric acid.

ie =Δ h /l, represent gradient formula where Δ h=potential drop and l is the average of last field in the flow net at the exit end.

Fully penetrating slot is used for both confined and unconfined case of flow.

Using the formula, hW = h -Z

In 1956, chapmen developed an expression for finding the discharge qP from a partially penetrating slot in an unconfined aquifer from his model studies.

According to practical suggestion given by A.Casagrande, every transition in the shape of curve is smooth, being either elliptical or parabolic in shape.

Complete design of dewatering system consists of the diameter and spacing of well points or wells, penetration of wells and the pumping capacities.

The seepage analysis is done on the assumptions that the flow is laminar and Darcy’s law is valid and further assumed that the soil to be dewatered is homogeneous and isotropic.

The graphical method of flow net construction first given by Forchheimer in 1930, based on trial sketching.