Discharge Over a broad Crested Weir | Jameel Academy

University of Duhok
College of Engineering
Civil Department
Fluid Mechanics – Practical
Fluid Laboratory
A Report About :
Discharge over a Broad Crested Weir
Student Name : Jameel Masoud Jameel
Class : B
Date of Experimental : 2 / 4 / 2018
Date of Submitting : 17 / 4 / 2018
Experiment No. : 2

Procedures :
1) Make sure that discharge Apparatus is leveled, broad crested weir are
available and placed carefully and normal to the Discharge apparatus
and note the Breadth and height of weir that required for calculation.
2) Fill the discharge apparatus (Open channel Place) with water until the
water flow from inlet tank to the discharge tank and flow over the
broad crested weir.
3) After water surface will steady, read the water surface height over
Wier and all water depth at another section by using point gauge
which is the apparatus placed on the water surface to read the height
of water.
4) Then, Write the times from the beginning of filling the discharge Tank
with water to the time that we want and note the volume collected
between this short time to compute the Actual Discharge.
5) Reaped the procedure to calculate the discharge of different Water
quantinty and its collected time.
Inlet Tank
Discharge Tank
Volumetric Tank
Point Gauge
Broad Crested Weir

Calculations and Results :
Note : Breadth of weir ( 𝐛) = 𝟕. 𝟑𝐜𝐦 , Height of weir ( 𝐏) = 𝟏𝟎𝐜𝐦
Example: If Volume = 20 lt . Time = 5 sec . H = 7.72cm
h = 5.45cm . Rotameter = 2.5 l/s
-The discharge can be calculated using the following formula :
Qth = h × b × √2g(H − h)
Qth = 0.073 × 0.0545 × √2g(0.0772 − 0.0545) = 2.66 m3
/sec
Qact =
Volume
Time
=
20
5
= 4 m3
/sec
Cd =
Qact
Qth
=
4
2.66
= 1.51
Details Table :
No.
Volume
(l)
Time
(sec)
Rotameter
(l/sec)
H
(cm)
h
(cm)
Qact
(l/sec)
Qth
(l/sec)
Cd
1 20 5.00 2.50 7.72 5.45 4.00 2.66 1.51
2 15 5.91 2.50 7.60 5.10 2.54 2.61 0.97
3 15 6.00 2.40 7.40 4.90 2.50 2.51 1.00
4 15 6.49 2.30 7.30 4.75 2.31 2.45 0.94
5 5 2.10 2.20 6.55 4.30 2.38 2.09 1.14
2.00
2.50
3.00
3.50
4.00
4.50
6.40 6.60 6.80 7.00 7.20 7.40 7.60 7.80
Qact(l/sec)
H (cm)
Relationship Between Q act & H
𝐐 = 𝟎. 𝟎𝟓𝟖𝟕𝐇 𝟏.𝟗𝟐𝟐𝟖

Discussion and Conclusion :
In this test we determine the discharge using an artificial Channel having
and obstruct (broad crest weir) and making the ratio between the actual
and theoretical discharge, finally we got a result after doing all procedure
accurate which is the discharge over broad crest weir, as shown in our
result that with increasing Water depth it will increase the ratio between
actual Discharge and theory, and we found the logarithm equation of
determining the ratio between actual Discharge and Height of Water, by
using the Gauge reading. the errors that maybe we did is unbalancing the
discharge Apparatus, and another one when reading the Actual
Discharge of water such our reading (4 𝑙/𝑠𝑒𝑐 ) that is the different
discharge from another Discharge and make the cd longer from another.
but with all condition we doing the test normally and accuracy.
In conclusion the purpose of this test is to determine the discharge over
broad crest weir and compare it with theory, and compute the ratio
between actual and theory. Finally, we know that how test was doing and
how to compute the theory discharge and actual using the small Artificial
channel.

Discharge Over a broad Crested Weir | Jameel Academy

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Discharge Over a broad Crested Weir | Jameel Academy