Question

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

Answer 1

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.