The manning’s coefficient for a lined trapezoidal channel with a bed slope of 1 in 4000 is 0.014 and it will be 0.028 if the channel is unlined. The area in the case of the lined section is 19.04 m^2 and for the unlined section is 29.09 m^2. What percentage of earthwork is saved in a lined section relative to an unlined section, when a hydraulically efficient section is used in both the cases?

Question

The manning’s coefficient for a lined trapezoidal channel with a bed slope of 1 in 4000 is 0.014 and it will be 0.028 if the channel is unlined. The area in the case of the lined section is 19.04 m^2 and for the unlined section is 29.09 m^2. What percentage of earthwork is saved in a lined section relative to an unlined section, when a hydraulically efficient section is used in both the cases?

asked Jul 31, 2023 in Irrigation Engineering by Carter (75.2k points)

The manning’s coefficient for a lined trapezoidal channel with a bed slope of 1 in 4000 is 0.014 and it will be 0.028 if the channel is unlined. The area in the case of the lined section is 19.04 m^2 and for the unlined section is 29.09 m^2. What percentage of earthwork is saved in a lined section relative to an unlined section, when a hydraulically efficient section is used in both the cases?

(a) 24.44 %

(b) 34.55%

(c) 50%

(d) 37.66%

This question was posed to me by my school principal while I was bunking the class.

The above asked question is from Irrigation Channels Design topic in division Sediment Transport and Irrigation Channels Design of Irrigation Engineering

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Greg · Answer 1 · 2023-08-15T08:25:40+0000

Right choice is (b) 34.55%

To elaborate: The percentage of earthwork saving due to the lining is (A2 – A1)/A2 x 100.

= (29.09 – 19.04) / 29.09 x 100

= 34.55%.

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