The dimensionless terms are the transfer parameters relating 

 phenomena of different scale. The multiplicity of these parameters 

 makes the possibility of a true model experiment of bar processes 

 questionable, if not negative. It is possible, however, that approxi- 

 mate models which ignore the least important terms are sufficient. 



P 



The term, -^, may be omitted because the densities are constant. 



If it is assumed that hydrodynamic effects on the motion of sand are 

 independent of the Reynolds number, the parameter containing the 

 kinematic viscosity also may be eliminated. With these simplifica- 

 tions, 



<m 



To obtain the equation for the bar after it is relatively stable, Hb may 

 replace H'b and the term involving time be omitted. Accordingly, 



or omitting a^, which may be a constant for a series of tests. 



The last expression suggests that the effect of wave height, ag, and 

 the bar base depth Hb can be conveniently related by plotting aoIHe 

 against the wave steepness ratio ao/Xo- 



B. Depth and form of bars. — The depth of the bar crest below the 

 water surface (He in fig. 1) is the highest point of the bar and therefore 

 is probably a critical feature. It may then be assumed that a relation- 

 ship exists between the bar depth, the wave characteristics and the 

 nature of the sand. The general expression 



\ tto Ao aoM / 



is obtained from dimensional analysis by assuming that the bar is 

 relatively stable and the effect of kinematic viscosity is negligible. In 

 view of equation 3, HJqo may be replaced by HJHb, giving 



If (r<p is the same in all tests it suffices to write 



