(e) attainment of stable equilibrium form; and 



(f) erosion and ultimate disappearance of bed forms 

 at high water velocities. 



This experimental study deals with all these stages in varying degree, 

 as have the previous investigations which are discussed in Section 1,3. 



Sketches of regular and irregular ripple profiles with definitions 

 of their dimensions are shown in Figure 1. 



2. Dimensionless Variables. 



Interpretation of ripple observations is made easier by the use 

 of dimensionless variables. This study adopts, with slight modification, 

 the system advanced by Yalin and Russell (1962) . The four independent 

 dimensionless variables are: 



a_ _s 

 D ' p 



where 



g(^-l)D (1) 



, 1/2 

 ;(^-1)d3 



2a = orbital diameter of the fluid motion 



D = average grain diameter 



p p = densities of sand and fluid 



g = acceleration due to gravity 



U = maximum velocity of the fluid 



V = kinematic viscosity of the fluid 



C2) 



