Question

Standard stilling basin is provided at the toe of a dam spillway for energy dissipation is usually provided with auxiliary devices like chute blocks and dentated sills for the basic purpose of reducing the length of the stilling basin from about ________________

(a) 6 y2 to 4 y2

(b) 4 y2 to 2 y2

(c) 6 y2 to 2 y2

(d) 3 y2 to y2

This question was addressed to me in quiz.

My doubt is from Energy Dissipation Below Overflow Spillway topic in division Spillways, Energy Dissipators and Spillway Gates of Irrigation Engineering

Answer 1

Correct choice is (a) 6 y2 to 4 y2

To explain: In the case of dams and spillways, the jump is steady and the length of the jump is almost constant and is equal to 6 y2 where y2 is the post jump depth. The length of the basin is related to Froude number as the economy in the length of the basin up to about 35% i.e. 4.3 y2 is thus obtained for auxiliary devices.