Determination of Kennedy’s Parameter j for Dunes

The purpose of this note is to suggest a method for the evaluation of j when the sand waves are dunes and the flow is sufficiently tranquil. The development of this method enables the use of Kennedy’s expressions to predict sand wave lengths according to his 1963 theory that the dimensionless wave number is a function of the Froude number and of j (a dimensionless quantity). The determination of j rests on the simultaneous considerations of the relations of Kennedy and Yalin for determining Λ. Assuming that the methods of Kennedy and Yalin are equally valid, one can eliminate Λ from the equations and see that j is determined as a certain function of the Reynolds number and the relative skin roughness.