unstable and the profile consequently being unpredictable. 



A series of experiments were made to determine the amounts of 

 material that were thrown into suspension due to the action of the 

 waves on a beach. All of the tests indicated that the maximum con- 

 centration of suspended material occurred in the breaker region. 

 It was also observed that the orientation of the sampling tube in the 

 wave stream affected the measured concentration of the sand particles. 



Because of the number of waves required to develop a stable con- 

 dition in the model beaches for the particular wave periods used, it 

 is questionable whether a corresponding prototype beach in nature, 

 under the natural wave and tidal actions, would result in an equilibrium 

 state . 



The qualitative observations made on ripple formation indicate 

 that the wave height appeared to be the controlling element in forming 

 the size and shape of the ripple. A wave of greater amplitude, having 

 a relatively large particle movement, gave greater ripple amplitudes 

 and spacing than the wave heights of lower amplitudes. 



Recommendations 



After a review of recent literature on wave action on granular 

 material and in view of the rather limited tests discussed above, it 

 appears desirable that further study of two-dimensional wave action 

 be conducted on the following problems- 



a. In the light of recent investigations on wave forces on 

 particles* a comprehensive study should be made on the forces which 

 cause bed movement by wave action. The variables in these tests should 

 include the wave characteristics and the specific gravity and mechani- 

 cal analysis of the material. 



b. The movement of sand exposed to two-dimensional wave motion 

 and the nature of profile changes should be investigated under con- 

 ditions where a tide is introduced and where the wave characteristics 

 are changed, 



c„ Observations under the controlled conditions of a wave channel 

 should be made on the nature of suspended-matter distribution in and 

 near the surf zone. The variables should include the characteristics 

 of both the sediment and the waves. 



Influence of Groins on Beach Stabilization 



Erosion of a beach occurs when the supply of sand to it is less 

 than the rate at which the sand is transported along the beach. To 

 control erosion groin systems often are used to promote the accretion 

 and stabilization of beaches where the littoral drift induced by the 



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