86. A channel with a mild slope is followed by a horizontal channel and then by a steep channel. What gradually varied flow profiles will occur?

1. 1. M₁, H₁, S₁

   
   
   

   2. M₂, H₂, S₂

   
   
   

   3. M₁, H₂, S₃

   
   
   

   4. M₁, H₂, S₂

   
   
   

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1. View Hint View Answer Discuss in Forum

   The given profile: y > y_n > y_c, i.e. m₁.
   From horizontal to steep sloped, there will be draw down.
   ∴ it is H₂ and on steep sloped channel, it is S₂.

   Correct Option: D

   The given profile: y > y_n > y_c, i.e. m₁.
   From horizontal to steep sloped, there will be draw down.
   ∴ it is H₂ and on steep sloped channel, it is S₂.

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87. Identify the FALSE statement from the following:— The specific speed of the pump increases with

1. 1. increase in shaft speed

   
   
   

   2. increase in discharge

   
   
   

   3. decrease in gravitational acceleration

   
   
   

   4. increase in head

   
   
   

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1. View Hint View Answer Discuss in Forum

   Ns =	N√Q
   	Hm3/4

   
   

   Ns ∝	1
   	Hm3/4

   Correct Option: D

   Ns =	N√Q
   	Hm3/4

   
   

   Ns ∝	1
   	Hm3/4

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88. There is a free overfall at the end of a long open channel. For a given flow rate, the critical depth is less than the normal depth. What gradually varied flow profile will occur in the channel for this flow rate?

1. 1. M₁

   
   
   

   2. M₂

   
   
   

   3. M₃

   
   
   

   4. S₁

   
   
   

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1. View Hint View Answer Discuss in Forum

   y_n > y_c
   ∴ Mild slope For free flow at end of long channel on mild slope, there is draw down and depth decreases from yn to yc and not below y_c.
   ∴ y_n > y > y_c.

   Correct Option: B

   y_n > y_c
   ∴ Mild slope For free flow at end of long channel on mild slope, there is draw down and depth decreases from yn to yc and not below y_c.
   ∴ y_n > y > y_c.

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89. As per the Lacey’s method for design of alluvial channels, identify the true statement from the following.

1. 1. Wetted perimeter increases with an increase in design discharge

   
   
   

   2. Hydraulic radius increases with an increase in silt factor

   
   
   

   3. Wetted perimeter decreases with an increase in design discharge

   
   
   

   4. Wetted perimeter increases with an increase in silt factor

   
   
   

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1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: A

   NA

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90. The flow rate in a wide rectangular open channel is 2.0 m³ /s per metre width. The channel bed slope is 0.002. The Manning’s roughness coefficient is 0.012. The slope of the channel is classified as

1. 1. Critical

   
   
   

   2. Horizontal

   
   
   

   3. Mild

   
   
   

   4. Steep

   
   
   

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1. View Hint View Answer Discuss in Forum

   yc =	q²	=		2²		1/3	= 0.742 m
   	g			9.81

   
   

   V =	1	R2/3S1/2(Manning’s equation)
   	n

   
   

   V =	q
   	yn

   
   

   ∴ q =	1	R2/3S1/2.yn
   	n

   
   

   2 =	1	×(yn)2/3 ⋅yn⋅(0.002)1/2
   	0.012

   
   R ≈ y_n (wide channel)
   ∴ y_n = 0.688 m.

   Correct Option: D

   yc =	q²	=		2²		1/3	= 0.742 m
   	g			9.81

   
   

   V =	1	R2/3S1/2(Manning’s equation)
   	n

   
   

   V =	q
   	yn

   
   

   ∴ q =	1	R2/3S1/2.yn
   	n

   
   

   2 =	1	×(yn)2/3 ⋅yn⋅(0.002)1/2
   	0.012

   
   R ≈ y_n (wide channel)
   ∴ y_n = 0.688 m.

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