Which of the following statements is correct as per Lacey's method for design of alluvial channels?

Question

Question

This question was previously asked in

BPSC AE Paper 6 (Civil) 11 Nov 2022 Official Paper

Answer 1

Concept:

Lacey gave three independent equation after intensive research in alluvium and gave the idea of regime.

The equations given by Lacey are:

\({\bf{v}} = √ {\frac{2}{5}{\bf{Rf}}}\)

\({\bf{A}}{{\bf{f}}^2} = 140{{\bf{v}}^5}\)

\({\bf{v}} = 10.8{{\bf{R}}^{\frac{2}{3}}}{{\bf{S}}^{\frac{1}{3}}}\)

As per lacey, the wetted perimeter P is given as

P = 4.75 √Q

Hence the wetted perimeter of the alluvial channel increases with an increase in design discharge.

Important Point:

Difference between Lacey and Kennedy theory are:-

Lacey Theory	Kennedy’s Theory
Lacey considered a semi-elliptical section	Kennedy considered a trapezoidal section
Lacey considered boundary material and defined the silt factor	Kennedy did not give any importance to boundary material.
Lacey gave the equation for the bed slope	Kennedy didn’t give any such equation
This theory applies to both the alluvial canal and river	This theory applies to alluvial canal only