Irrigation Water Conveyance and Application Methods
Subtopic: Design of irrigation channels and underground pipelines
Question Statement:
A fundamental difference between Kennedy's silt theory and Lacey's regime theory for designing unlined alluvial irrigation canals is that:
Options:
(A) Kennedy assumed silt-supporting vertical eddies are generated only from the channel bed, whereas Lacey recognized eddies are generated from the entire wetted perimeter
(B) Kennedy used hydraulic radius $R$ while Lacey strictly used flow depth $y$
(D) Kennedy designed regime channels whereas Lacey designed only lined concrete canals
Answer Key:
A
Step-by-Step Solution & Explanation
- Kennedy (1895) assumed that upward vertical eddies supporting silt particles are generated solely from the horizontal bed ($V_0 = 0.55 m y^{0.64}$).
- Lacey (1930) proved that silt-supporting turbulent eddies are generated from the entire wetted boundary (bed and sides), employing hydraulic radius $R$ and introducing the silt factor $f = 1.76 \sqrt{d_{mm}}$. Option A is correct.