machines for each stroke of the generating blades. The wave period is changed 

 at some predetermined interval (usually every 15 minutes), a sequence of three 

 different periods generally being used during any testing program. As a 

 consequence of changing the wave period the wave amplitude also changes. The 

 sandy beach and bottom sediments are moved in the downdrift direction by the 

 natural forces caused by the waves. Additional sand is added at the feeder 

 beach area to maintain the position of the still water line. Generally the 

 tests are 50 hours long (this means 50 hours of wave action on the beach with 

 time for hydrographic surveys and other necessary details excluded from the 

 wave-generation period). Shorter tests have been made in about 25 hours, while 

 some long tests have taken in excess of 300 hours of operating time. 



It is beyond the scope of this paper to discuss the objectives of a labora- 

 tory testing program, but it is proper to elaborate upon some of the goals which 

 may or can be achieved with the use of radioactive tracers, and which are diffi- 

 cult to develop by normal testing. One such objective would be the determina- 

 tion of the velocity with which individual particles move. Depending upon the 

 sensitivity of the detection system and the concentration of activated particles, 

 it is conceivable that the presence of a very few particles may be detected in 

 place. On the other hand, the utilization of autoradiographic techniques and a 

 minimum sampling program should permit the identification of a single particle. 

 Knowing the spatial distribution of the samples and the time history of the test 

 the rate of travel of the particles is then also known. It is also feasible to 

 discover the size of the activated particle by measuring the intensity of the 

 activity emitted by the particle. This could be done by calibrating particle 

 activity versus size (to be discussed later) for some fixed exposure time of 

 photographic film. 



Another objective which appears feasible is the definition of the zone of 

 sediments disturbed by the wave action. This zone may be defined by its origin. 

 As a deep water oscillatory wave passes through continually shallowing waters in 

 its approach toward land, the orbital velocity of a water particle becomes 

 sufficiently great to affect the sedimentary particles of the bottom. Under some 

 given conditions of wave amplitude and period and at some fixed depth it would 

 appear that the first effects of the orbital wave velocity are upon a layer of 

 sedimentary particles one particle thick. In this layer some few particles would 

 be thrown up into suspension by the wave action and others would be moved by 

 saltation and/or creep. As thf» water depth becomes increasingly shallow and as 

 waves approach the breaking zone, more of the bottom sediments are disturbed and 

 eroded. It is readily apparent that the increase in the number of sedimentary 

 particles set into motion must be caused by an increase in depth of the zone of 

 sediments disturbed by wave action,, In the breaking zone the extreme turbul- 

 ence of the breaking wave draws sedimentary particles of all sizes into suspension 

 and it is here that the greatest concentration of suspended sedimentary particles 

 occurs. As the wave becomes a wave of translation the turbulent action of the 

 wave continues to move the bottom particles by any or all of the three modes of 

 transportation mentioned above and the zone of sediments disturbed by wave action 

 is found to continue to the limit of wave uprush. It is readily apparent that 

 the areal extent and the depth of this zone of disturbed sediments is responsive 

 to thg wave climate occurring at the time, and changes as the wave conditions 

 change. It is believed that the definition of the areal extent and of the depth 

 of this zone can be made with the use of labelled sediments. A combination of 

 in situ monitoring, surface samples and subsurface cores should define this zone. 



The goal of many laboratory experiments is a quantitative relationship of 



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