A SAND FEEDER FOR USE IN LABORATORY LITTORAL TRANSPORT STUDIES 



by 



RUDOLPH P. SAVAGE 

 Research Division, Beach Erosion Board 



A model layout shown in Figure 1 is typical for laboratory studies 

 involving the transportation of sand (littoral drift) along a beach. 

 Basically this layout consists of a basin containing wave generators 

 aligned at an angle (30° in this case) to a sand beach. Located at the 

 downdrift end are sand traps (numbered 1-15) and accessory equipment re- 

 quired to remove the sand from the traps and transport it to a weighing 

 station. 



In operation, the wave generators produce waves which approach and 

 break on the sand beach at an angle to the general beach contours. In so 

 doing, these waves generate a current (the littoral current) which moves 

 alongshore away from the direc+ion of wave approach. Both that sand placed 

 in suspension by the breaking waves and carried in the littoral current, 

 and that propelled directly over the bottom by the waves, is then moved 

 along the beach. At some line perpendicular to the beach, the moving sand 

 is trapped and transferred to a weighing station to be measured. 



Since most littoral transport studies are attempting to represent an 

 infinitely long straight beach, the trapped sand (or other comparable sand) 

 should be supplied to the updrift end of the beach in a manner which simu- 

 lates the continuous supply of sand coming from an imaginary updrift beach 

 section. If too little or too much sand is supplied to the feeder beach, 

 the beach will erode or accrete and the angle between the beach and the 

 incoming waves will change, thus introducing an added variable to the study, 



In exploratory tests at the Beach Erosion Board, it was found that the 

 problem of properly feeding the test beaches is rather complicated for two 

 principal reasons. First, the rate at which the sand must be supplied is 

 unknown and is not usually the same as the rate at which sand is being 

 trapped; and second, the actual mechanical means of placing the sand con- 

 tinuously on the beach without interfering with the beach processes or 

 utilizing an exorbitant amount of hand labor were not available. However, 

 a satisfactory solution to the problem has been developed from an idea 

 given the author during a visit to the Coastal Engineering Laboratories of 

 the University of Denmark in Copenhagen. 



The solution consists of a sand feeder which is shown in Figure 2. 

 The body of the feeder is a hollow metal cylinder supported by a metal 

 framework and three adjustable legs. An overflow trough 5-1/2 inches deep 

 fits around the outside of the cylinder. The bottom of this trough is 6 

 inches below the top of the cylindrical body and the trough is drained by 

 a 2-1/2 -inch hose. 



