weighing device for recording the rate of littoral sand transport in- 

 duced by direct wave action and by the littoral current was installed 

 at the downbeach end. This device consisted of a metal hopper sus- 

 pended on a beam which rested on a fulcrum . On one end of the beam 

 a counterweight was attached (for zero setting), and the other end 

 of the beam rested on a sylphon bellows which was liquid-filled and con- 

 nected by tubing to a clock-driven Bourdon-type pressure recorder. The 

 recorder was calibrated by placing known weights into the sand hopper. 

 The efficiency of the sand trap was determined under operating con- 

 ditions by feeding known weights of sand into the flow at the entrance 

 to the unit. 



To insure that all sand transported along the beach would be 

 carried into the weighing device , it was necessary to indue© a flow in- 

 to the basin containing th® hopper. This pumping action was necessary 

 in order to prevent the littoral current , upon reaching the trap, from • 

 flowing seaward; sine© such a seaward current would oppose the waves, 

 sand deposition would occur in this region, and thus progressively 

 change the rate of transport into the trap. The flow from the pump 

 was returned to the main basin through a channel of relatively large 

 dimensions at a corresponding low velocity, so that no large scale 

 circulation was induced in the basin. Thus, the length of beach studied 

 approximated a section of beach of infinite length. The beach angle 

 was varied between 10° and 50° . 



Summary 



The following statements summarize the experimental work made on 

 the movement of one particular sand transported along a straight 

 beach unobstructed by fixation works. In the prototype the sand used 

 would correspond to pea gravely the stable model beach corresponds to 

 a prototype gravel beach. 



a. The waves impinging upon a beach set at 30° to the wave gene- 

 rator developed a greater rate of sand transport than did that created 

 by the beach set at a 10° angle. 



b. In the region of flat waves (low steepness ratios) the trans- 

 port rate sharply increases for small increases in the H /lL ratio, 

 until a peak value of around Hq/Lo ~ .0.023 is reached. Here, in this 

 region, the major portion of the sand that is moved drifts along the 

 beach as bed load, whereas in the region of steep waves (high steepness 

 ratios, Ho/Lo exceeding 0.025) the curve of the transport rate takes 



on a negative, or opposite, slope when compared to the curve for the 

 waves in the low steepness region. The* slope for the transport rate 

 curve is less steep and a small change in wave shape does not material- 

 ly affect the movement of sand. In the region of steep waves the sand 

 is moved by a combination of beach drift and that thrown up into sus- 

 pension, with the latter accounting for the principal amount of trans- 

 port. Most of the beach drift occurs at the toe of the beach face and 

 the material in suspension is carried along just shoreward of the off- 

 shore bar. 



