Notches

Notch is defined an opening provided in the side of a tank.The upstream liquid level below the top edge of the opening.The bottom edge over which the liquid flows is called the sill or crust of the notch.
The sheet of water flowing over the bottom edge of the notch is called nappe or vein.
The height of water above the sill of the notch is called the head of the notch.
Classification/Types of notches

1. According to the shape of the opening of the notch.
   The notches are classified as rectangular notch,triangular notch,trapezoidal notch,stepped notch.
2. According to the effect of side of opening
   The notches are classified as:
   (a) Notch with end contraction (If the notch width or length is less than the width of the channel it is known as notch with end contraction)
   (b) Notch without end contraction. (Notch width or length extends over the full width of the channel in which it based known as notches without end contraction)