Who proposed the Silt Theory for the design of stable irrigation channels?
Analysis & Theory
Lacey proposed the Silt Theory in 1930 for the design of regime channels in alluvial soils.
According to Lacey’s theory, the regime velocity (V) is given by:
Analysis & Theory
Lacey's regime velocity formula is V = (Qf²/140)^(1/6), where Q is discharge and f is silt factor.
In Lacey's theory, the silt factor (f) depends on:
Analysis & Theory
Silt factor f = 1.76 √d, where d is the mean particle size in mm.
The wetted perimeter (P) of a channel in Lacey's theory is given by:
Analysis & Theory
According to Lacey, P = 4.75√Q, where Q is discharge in m³/s.
According to Lacey's theory, the regime channel slope (S) is:
B
S = f^(5/3) / (3340Q^(1/6))
Analysis & Theory
The regime slope formula is S = f^(5/3) / (3340Q^(1/6)).
Lacey’s theory is applicable to:
A
Rigid boundary channels
Analysis & Theory
Lacey’s theory is applicable only to regime channels flowing through alluvial soils.
The hydraulic radius (R) in Lacey’s theory is given by:
Analysis & Theory
According to Lacey, R = 5V/3f, where V is velocity and f is the silt factor.
A regime channel is one that:
C
Remains in equilibrium without silting or scouring
Analysis & Theory
A regime channel is stable and neither silts up nor scours under prevailing conditions.
Which of the following is a limitation of Lacey’s Silt Theory?
A
Applicable to all types of soils
B
Assumes non-uniform flow
D
Based on non-alluvial beds
Analysis & Theory
One limitation is that Lacey’s theory does not explicitly consider variable sediment loads.
The silt factor (f) in Lacey’s theory increases with:
A
Decrease in particle size
Analysis & Theory
Silt factor increases with larger particle size since f = 1.76 √d.