Question

The Lacey’s scour depth R given by equation R = 0.473 (Q/f)^1/3 is applicable when the river width is equal to ___________

(a) actual river width

(b) regime width

(c) any contracted width

(d) span length

This question was addressed to me in final exam.

The doubt is from Culverts Construction in section Culverts and Small Road Bridges Construction of Irrigation Engineering

Answer 1

Correct option is (b) regime width

To elaborate: For a purely alluvial stream having a span length (L) equal to regime width (W), Lacey’s regime scour depth is given by R’ = 0.473 (Q/f)^1/3.

Silt factor (f) is obtained by the equation f = 1.76 d^1/2 where d is the average size of particle in mm.