short-period wave and current patterns, the following procedure was used to 

 select a tracer material. Using the prototype sand characteristics (median 

 diameter, D^q = 0.52 mm (0.02 in.), specific gravity = 2.65) and assuming the 

 horizontal scale to be in similitude (i.e., 1:100), the median diameter for a 

 given specific gravity of tracer material and the vertical scale were computed. 

 The vertical scale was then assumed to be in similitude and the tracer median 

 diameter and horizontal scale were computed. This resulted in a range of 

 tracer sizes for given specific gravities that could be used. Although several 

 types of movable-bed tracer materials were available at WES, previous investi- 

 gations (Giles and Chatham 1974, Bottin and Chatham 1975) indicated that 

 crushed coal tracer more nearly represented movement of prototype sand. 

 Therefore, quantities of crushed coal (specific gravity = 1.30; median diameter, 

 DgQ =1.18 mm (0.046 in.)) were prepared for use as a tracer material through- 

 out the model investigation. 



13 



Chapter 2 The Model 



