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We were discussing the basic difference between orifice and mouthpiececlassification of orifices and mouthpiecesadvantages and disadvantages of orificeshydraulic coefficientsexperimental process to determine the hydraulic coefficientsflow through fully submerged orificeflow through partially submerged orificetime of emptying a tank through an orifice fitted at its bottom, time of emptying a circular horizontal tank through an orifice and also time of emptying a hemispherical tank through an orifice in the subject of fluid mechanics in our recent posts. 

Now we will go ahead to find out the basic concepts of Notches and weirs. We will also see here the difference between notches and weirs with the help of this post. 


Notch is basically defined as a device which is used for determining the flow of liquid through a small channel or a tank. 

Notches might be defined as the opening provided in one side of a tank or reservoir or a small channel in such a way that the liquid surface in the tank or channel is below the top edge of opening.  

Bottom edge of notch over which liquid flows will be termed as sill or crest. The material of casting of notch will be usually a metallic pipe. 

Notches will be small in size and will be preferred to use for measuring the small discharge of small stream or canal. 

Type of notches 

There are following types of notches as mentioned here.
  1. Rectangular Notch 
  2. Triangular Notch or V- notch 
  3. Trapezoidal Notch 
  4. Stepped Notch 


A weir will be basically a concrete or masonary structure which will be located in an open channel over which flow will take place. 

We can also define as the structure constructed across the river or large canal for storing water on upstream side. 

Top of weir over which water flow will take place will be termed as crest. 

Weir will be used for measuring the large discharge of rivers or large canals. 

Weir will be usually in the form of vertical wall, with a sharp edge at the top, running all the way across the open channel. 

Notches will be small in size but weir will be bigger in size. 

A weir will be basically made by a concrete or masonary structure. 

Type of weirs 

There are following types of weirs as mentioned here.
  1. Rectangular weir
  2. Cippoletti weir
  3. Ordinary weir
  4. Submerged or drowned weir
  5. Narrow crested weir
  6. Broad crested weir
  7. Sharp crested weir
  8. Ogee weir 
Now we will go ahead to find out the classifications of notches and weirs, in the subject of fluid mechanics, in our next post. 

Do you have any suggestions? Please write in comment box. 


Fluid mechanics, By R. K. Bansal 
Image Courtesy: Google 

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