# Calculate the effective length of the spillway which consists of 6 spans having a clear width of 10 m each. The thickness of each pier may be taken as 2.5 m and the total design head on the crest including velocity head is 16.3 m. Assuming 90° cut water nose piers and rounded abutments.

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Calculate the effective length of the spillway which consists of 6 spans having a clear width of 10 m each. The thickness of each pier may be taken as 2.5 m and the total design head on the crest including velocity head is 16.3 m. Assuming 90° cut water nose piers and rounded abutments.

(a) 55 m

(b) 60 m

(c) 65 m

(d) 75 m

I have been asked this question in an internship interview.

Origin of the question is Ogee Profile in division Spillways, Energy Dissipators and Spillway Gates of Irrigation Engineering

by (106k points)
The correct choice is (a) 55 m

Explanation: The effective length of the spillway is given by-

Le = L – 2[N.Kp + Ka].H

Where  L = clear length of the spillway crest = 6 x 10 = 60, N = Number of piers = 5 and H = 16.3 m

For 90° cut water nose piers and rounded abutments; Ka = 0.1 and Kp = 0.01

Le = 60 – 2[5 x 0.01 + 0.1] x 16.3 = 55.1 m.

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