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# MCQs on Discharge Over different type of weirs

In discharge of water over narrow crested weir, head of water is directly proportional to Discharge Coefficient.

a) True

b) False

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b

Explanation: In discharge of water over narrow crested weir, head of water is inversely proportional to Discharge Coefficient.

In discharge of water over narrow crested weir, discharge is directly proportional to the cube root of acceleration due to gravity.

a) True

b) False

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b

Explanation: In discharge of water over narrow crested weir, discharge is directly proportional to the square root of acceleration due to gravity.

In discharge of water over ogee weir, discharge is directly proportional to the second power of length.

a) True

b) False

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b

Explanation: In discharge of water over ogee weir, discharge is directly proportional to the first power of length.

For discharge over ogee weir discharge is directly proportional to length but for discharge over narrow crested weir it is inversely proportional to length.

a) True

b) False

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b

Explanation: For both weirs it’s same.

An Ogee weir 5 m long had a head of 40 cm of water. If CD = 0.61, find the discharge over the weir.

a) 2.9 m3/s

b) 2.3 m3/s

c) 3.1 m3/s

d) 3.3 m3/s

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a

Explanation: Q = 0.67 * Cd * L * √2g * H1.5

Q = 2.3 m3/s.

The height of water on upstream and downstream side of a submerged weir of 4 m length are 24 cm and 13 cm. If Cd for free and drowned portions are .62 and .78 respectively, find the discharge over the weir.

a) .85 m3/s

b) 1.35 m3/s

c) 3.2 m3/s

d) .55 m3/s

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a

Explanation: Q = 0.67 * Cd1 * L * √2g * H1.5 +. Cd2 * L * h * √2g(H – h)

= .67 * .6 * 3 * √2g * (.24 – .13)1.5 + .8 * 3 * .13 √2g(.24 – .13)

= .85 m3/s.

An Ogee weir 3.4 m long had a head of 40 cm of water. If CD = 0.63 find the discharge over the weir.

a) 1.61 m3/s

b) 2.5 m3/s

c) 3.1 m3/s

d) 3.3 m3/s

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a

Explanation: Q = 0.67 * Cd * L * √2g * H1.5

Q = 1.61 m3/s.

The height of water on upstream and downstream side of a submerged weir of 4 m length are 23.5 cm and 14 cm. If Cd for free and drowned portions are .61 and .75 respectively, find the discharge over the weir.

a) m3/s

b) 1.35 m3/s

c) 3.2 m3/s

d) .55 m3/s

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a

Explanation: Q = 0.67 * Cd1 * L * √2g * H1.5 +. Cd2 * L * h * √2g(H – h)

= .67 * .6 * 3 * √2g * (.24 – .13)1.5 + .8 * 3 * .13 √2g(.24 – .13)

= .85 m3/s.

In discharge of water over narrow crested weir, discharge is directly proportional to the second power of height.

a) True

b) False

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b

Examples: In discharge of water over narrow crested weir, discharge is directly proportional to the one and half power of height.

In discharge of water over Ogee weir, discharge is directly proportional to the first power of length.

a) True

b) False

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a

Explanation: This is as per empirical relation.