Weirs are barriers placed in flowing water to alter flow characteristics and measure discharge. They come in various forms smaller than conventional dams. The geometry of the weir crest allows depth of water behind it to be converted to a flow rate using discharge equations. Common weir types include labyrinth, broad crested, sharp crested, compound, and V-notch weirs, each suited to different flow measurement applications. While weirs enable flow measurement, they can also increase oxygen in water and create dangerous hydraulic jumps downstream.

1. WELCOME TO MY TOPIC
WEIRS - (flow measuring)

2. WEIR
• its a barrier across the flowing fluid
designed to alter the flow characteristics.
• it is used to prevent flooding, measure
discharge, and render the river navigable.
• it take forms of obstructions smaller than
the conventional dams.

3. • Since the geometry of top of the weir is
known and all water flows over the weir,
depth of water behind the weir can be
converted to a rate of flow.
• discharge can be summarized as;
Q=CLHn

4. • When used for flow measurement it is
important that the weir crest is free of rust
or impurities.
• Roughness of any form will cause the weir
to discharge more water than indicated by
the standard discharge equations or
tables.

5. TYPES
1.LABYRINTH WEIR
It uses a trapezoidal shaped weir geometry
to increase the weir length. They are versatile
structures and can be modified to many
applications.

8. 2. BROAD CRESTED WEIR
It is a flat crested structure, with long
crest compared to flow thicknes. When the
crest is broad, the streamlines become
parallel to the crest invert and the
pressure distribution above the crest is
hydrostatic.

11. 3. SHARP CRESTED WEIR
It allows the water to flow cleanly away
from weir. Also known as FAYOUM weir.
These weirs are typically .25 inch (6.4
mm) or thinner metal plates. They are in
many shapes and styles like rectangular, v
notch and cipoletti weirs.... It can exhibit
accuracies to about +/-2%.

15. 4. COMPOUND WEIR
For accurate flow measurement
over a wider range of flow rates, a
compound weir combines two or more
types -typically a v-notch weir with a
rectangular weir. These weirs are intented
to measure no more than 35% of the
pipe's open channel flow capacity.

18. 5. V-NOTCH WEIR
Is a triangular channel section, used to
measure small discharge values. The upper
edge of the section is always above the water
level, so the channel is always triangular
simplifying calculation. V-notch weirs are
preferred for low discharges as head above the
weir crest is more sensitive to changes in flow
compared to rectangular weirs.

19. V-notch weirs typically achieve
accuracies of 2-5% . V-notch weirs are
sized between 22-1/20
and 1200
, with 22-
1/20
,300
,450
,600
,900
and 1200
the common
increments- although the free flow
discharge equations can be developed
from one universal equation for v-notch
weirs from 250
to 1200
in size.

21. DRAW BACKS
• Typically increases the oxygen content of
the water which brings a detrimental effect
on the ecology of the local water bodies.
• Even though the water around weirs can
often appear relatively calm, they can be
extremely dangerous places to boat,
swim, etc..as the circulation patterns on
the downstream side typically known as
hydraulic jump, can submerge a person
indefinitely.

22. • It can become a point where the garbage
and other wastes accumulates.

23. THANK U
ALL