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.

EA= extra length factor, which is a function of the ratio of slot penetration p to the thickness of pervious stratum b.

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

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.

Based on Dupuit-Forchheimer assumptions, the slope of the drawdown curve was assumed to be equal to hydraulic agent.

The flow lines and equipotential lines always meet at right angles to one another.

Where the dewatering system consists of a number of closely spaced well points or wells a simplified solution can be obtained by considering the lines of wells equivalent to a linear drainage slot.

The portion between any two successive flow lines is called a flow channel and the portion enclosed between two successive equipotential lines and successive flow lines are known as field.

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