Difference between kennedy's and lacey's theory
Answers
1. The basic concept regarding silt transportation is the same in both the theories. In both the theories it is stated that the silt remains in suspension due to vertical force of eddies.
2. Kennedy assumes that the eddies are generated on the bed only and hence he derives the formula for finding out critical velocity in terms of depth.
3. Lacey proposes that regime section is semi-circular ultimately and eddies are generated along the whole wetted perimeter. He drives formula for mean regime velocity in terms of hydraulic mean radius. 3 Lacey states that as the shape of irrigation channel is fixed to a particular geometrical figure (generally trapezoidal) it cannot achieve final regime conditions and hence may be said to achieve initial regime. Kennedy assumes that when there is neither silting nor scouring the channel is in its regime.
The fundamental concept concerning silt transport is identical in both theories. In both the hypotheses, it is asserted that the silt persists in suspension due to the perpendicular force of eddies.
Kennedy chooses Kutter’s formula for composing an irrigation channel. But in Kutter's equation value of N is arbitrarily established. However, Lacey has not set any value arbitrarily.
Kennedy has made application of the term “CVR” (m) but he did not give any explanation for determining m. He clearly states that it is depended on silt grade and silt charge.
Lacey suggests that management section is semi-circular sequentially and eddies are formed along the complete wetted boundary. He drives equation for mean regime impetus in terms of hydraulic mean radius.
Lacey has proposed the name “silt factor” (f). He associated f to mean breadth of the bed substance and gave basis to determine f.