This document summarizes a lecture on notches and weirs for fluid mechanics. It introduces notches as devices for measuring liquid flow rates through small channels or tanks. Weirs are described as concrete or masonry structures placed in open channels that water flows over. The document discusses that the discharge equation is the same for rectangular notches and weirs, and involves the length, head of water, theoretical velocity, and discharge coefficient. It provides two numerical problems applying this equation to calculate discharge for a notch and to determine the required weir height.

1. KALI CHARAN NIGAM INSTITUTE OF
TECHNOLOGY, BANDA
LECTURE
ON
NOTCHES AND WEIR
FLUID MECHANICS AND FLUID MACHINE(KME302)
( III SEMESTER )
BY : DEEPAK KUMAR YADAV
ME DEPARTMENT

2. INDRODUCTION
NOTCH : A notch is a device used for measuring for
rate of a liquid through a small channel or a tank.
WEIR: A weir is a concrete or masonary structure,
placed in open channel over which the flow occurs.
It is generally in the form of vertical wall, with a
sharp edge at the top , running all the way across
the open channel.

3. DISCHARGE OVER A RECTANGULAR
NOTCH OR WEIR
The expression for discharge notch or weir is the
same.
Let H = Head of water over the crest
L = Length of the notch or weir.
The area of strip = L×dh
and theoretical velocity of water flowing through
strip=

4. DISCHARGE OVER A RECTANGULAR
NOTCH OR WEIR
The discharge dQ, through strip is
dQ= Cd×Area of strip × Theoretical velocity
Total discharge Q,

5. NUMERICAL
• PROBLEM 1 : Find the discharge of water flowing
over a rectangular notch of 2m length when the
constant head over the notch is 300mm. Take
Cd=0.6.
• PROBLEM 2: Determine the height of a rectangular
weir of length 6m to be built across a rectangular
channel. The maximum depth of water on the
upstream side of the weir is 1.8m and discharge is
2000 lt/s. Take Cd=0.6. [AKTU 2015-16]

6. THANK YOU