What is the fundamental concept behind Kennedy’s theory for the design of stable irrigation channels in alluvial soils?
- AThe velocity of flow should be kept below the critical velocity to prevent scouring.
- BSilt is kept in suspension by the vertical component of eddies generated from the channel bed.Correct
- CThe channel width is the primary factor for ensuring stability.
- DThe bed slope should be as steep as possible to increase the discharge capacity.
Solution
Concept
Kennedys alluvial channel silt suspension mechanism
Formula
V0 = 0.55 × m × y0.64
Step-by-step solution
1. R.G. Kennedy formulated his silt theory based on observations on the Upper Bari Doab Canal system. 2. He postulated that flowing water generates turbulent eddies due to surface roughness. 3. Kennedy assumed that only vertical components of eddies generated from the channel bed keep silt in suspension. 4. He neglected eddies generated from the sloping side walls of the channel. Answer: B
Explanation
Kennedy's silt theory assumes that silt in an alluvial channel is kept in suspension solely by the upward vertical components of turbulent eddies generated from the channel bed. The sides of the channel are assumed to generate negligible eddies capable of supporting silt.
Why the other options are wrong
A) Critical velocity prevents both silting and scouring, but the fundamental physical mechanism is eddy suspension. C) Silt suspension by eddies, not width, is the foundational premise. D) Steep slopes increase scouring rather than maintaining regime stability.
Shortcut
Kennedy silt theory = Silt held in suspension solely by bed-generated vertical eddies.
Common mistake
Believing Kennedy considered eddies from both bed and sides (which was Lacey's key refinement).
Correct answer: B) Silt is kept in suspension by the vertical component of eddies generated from the channel bed.