The Constructor

Flow Net ā€“ Properties and Applications

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A Flow net is a graphical representation of flow of water through a soil mass. It is a curvilinear net formed by the combination of flow lines and equipotential lines. Properties and application of flow net are explained in this article.

Flow lines represent the path of flow along which the water will seep through the soil. Equipotential lines are formed by connecting the points of equal total head.

Fig 1: Flow Net

Properties of Flow Net

Properties of flow net are as follows:

Applications of Flow Net

Flow net is useful to determine the following parameters in seepage analysis of soil :

  1. Rate of Seepage loss
  2. Seepage Pressure
  3. Uplift Pressure
  4. Exit Gradient

1. Rate of Seepage loss (Q)

Using flow net, the rate of seepage loss or seepage quantity can be determined using the below expression :


k = coefficient of permeability

H = Head causing flow

Nf = Number of flow lines

Nd = Number of Equipotential lines

2. Seepage Pressure (Ps)

Seepage pressure at any point is determined by using the below mentioned formula :


h = Hydraulic potential after ā€œnā€ potential drops. It can be expressed as :


3. Uplift Pressure (Pu)

The uplift pressure at any point within the soil mass can be found using the undermentioned formula. It is also called as hydrostatic pressure.


4. Exit Gradient (iexit)

The exit gradient is the hydraulic gradient at the downstream end of flow line where seepage water from the soil mass joins with free water at the downstream. Exit gradient can be expressed as :


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