Design of Stable Channels

Question 1
An unlined canal under regime conditions along with a silt factor of 1 has a width of flow 71.25m. Assuming the unlined canal as a wide channel, the corresponding average depth of flow (in m, round off to two decimal places) in the canal will be ______________
A
1.25
B
4.58
C
3.82
D
2.94
GATE CE 2021 SET-1   Irrigation Engineering
Question 1 Explanation: 


R = D (for wide rectangular channel)
\begin{aligned} &\begin{aligned} A f^{2} &=140\left(\frac{2}{5} f R\right)^{5 / 2} \\ (B D) f^{2} &=140\left(\frac{2}{5} f \times D\right)^{5 / 2} \\ (71.25 \times D) \times 1 &=140\left(\frac{2}{5} \times 1 \times D\right)^{5 / 2} \\ D \times 0.5089 &=\left(\frac{2}{5}\right)^{5 / 2} \times(D)^{5 / 2} \\ D^{3 / 2} &=5.029 \\ \text { or } \qquad \qquad \qquad \qquad D &=2.94 \mathrm{~m} \end{aligned} \end{aligned}
Question 2
The depth of flow in an alluvial channel is 1.5 m. If critical velocity ratio is 1.1 and Manning's n is 0.018, the critical velocity of the channel as per Kenedy's method is
A
0.713 m/s
B
0.784 m/s
C
0.879 m/s
D
1.108 m/s
GATE CE 2009   Irrigation Engineering
Question 2 Explanation: 
The critical velocity as per Kennedy's method is
given by,
\begin{aligned} V_{0} &=0.55 \mathrm{my}^{0.64}=0.55 \times 1.1 \times(1.5)^{0.64} \\ &=0.784 \mathrm{m} / \mathrm{s} \end{aligned}
Question 3
A stable channel is to be designed for a discharge of Q m^{3}/s with silt factor f as per Lacey's method. The mean flow velocity (m/s) in the channel is obtained by
A
[\frac{Qf^{2}}{140}]^{1/6}
B
[\frac{Qf}{140}]^{1/3}
C
[\frac{Q^{2}f^{2}}{140}]^{1/6}
D
0.48*[\frac{Q}{f}]^{1/3}
GATE CE 2008   Irrigation Engineering
Question 4
As per the Lacey's method for design of alluvial channels, identify the TRUE statement from the following :
A
Wetted perimeter increases with an increase in design discharge.
B
Hydraulic radius increases with an increase in slit factor.
C
Wetted perimeter decreases with an increase in design discharge
D
Wetted perimeter increases with an increase in slit factor.
GATE CE 2007   Irrigation Engineering
Question 4 Explanation: 
As per Lacey's method of design of alluvial channels,
P=475 \sqrt{Q}
Question 5
A launching apron is to be designed at downstream of a weir for discharge intensity of 6.5 m^{3}/s/m. For the design of launching aprons the scour depth is taken two times of Lacey scour depth. The silt factor of the bed material is unity. If the tailwater depth is 4.4 m, the length of launching apron in the launched position is
A
\sqrt{5}m
B
4.7m
C
5m
D
5\sqrt{5}m
GATE CE 2005   Irrigation Engineering
Question 5 Explanation: 
Lacey's scour depth,
\begin{aligned} R=1.35\left(\frac{q^{2}}{f}\right)^{1 / 3}&=1.35 \times\left(\frac{6.5^{2}}{1}\right)^{1 / 3}=4.7 \mathrm{m} \\ \text{Scour depth }&=2 R=9.4 \mathrm{m} \\ \therefore \quad D&=2 R-4.4=5 \mathrm{m} \end{aligned}
Question 6
On which of the canal systems, R.G. Kennedy, executive engineer in the the Punjab Irrigation Department made his observations for proposing his theory on stable channels ?
A
Krishna Western Delta canals
B
Lower Bari Docab canals
C
Lower Chenab canals
D
Upper Bari Doab canals
GATE CE 2005   Irrigation Engineering
There are 6 questions to complete.

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