Taking lead from the Kennedy theory Mr. Gerald Lacey undertook detailed study to evolve more scientific method of designing irrigation channels on alluvial soils. He presented revised version of his study in 1939 which is popularly known as Lacey’s theory. In this theory, Lacey described in detail concept of regime conditions and rugosity coefficient. The definitions of these terms are already given.
It may be seen that for a channel to achieve regime condition following three conditions have to be fulfilled:
i. Channel should flow uniformly in “incoherent unlimited alluvium” of same character as that transported by the water;
ii. Silt grade and silt charge should be constant; and
iii. Discharge should be constant.
These conditions are very rarely achieved and are very difficult to maintain in practice. Hence according to Lacey’s conception regime conditions may be subdivided as initial and final. The definitions of these two terms are already given earlier.