PART V: CROSS -SHORE TRANSPORT RATE 



297. If a beach profile is not in equilibrium with the existing wave 

 climate, sediment will be redistributed along it to produce an equilibrium 

 profile shape in which state the incident wave energy will be dissipated 

 without causing further significant net sediment movement. It has been 

 established that as sediment is transported across the shore certain charac- 

 teristic net transport rate distributions occur, and these distributions have 

 specific properties in time and space. Regularity in transport rate distribu- 

 tions is anticipated since the previous chapter showed that the shape of the 

 beach profile changed regularly through time. 



298. The objective of this chapter is to describe properties of the 

 cross-shore sand transport rate and relate them to wave parameters, sand 

 characteristics, and beach profile shape. Quantitative knowledge of cross - 

 shore transport provides the necessary foundation for the numerical modeling 

 component of this investigation. 



299. Keulegan (1948) appears to have been the first to measure cross - 

 shore sand transport along the profile. He used traps mounted in a small wave 

 tank and found that the maximum transport rate was located at the point of 

 impending wave breaking where the front of the wave was almost vertical near 

 the crest. He noted a correlation between the sand transport rate and total 

 displacement of the water surface, and he recognized the existence of a 

 critical wave height for sand transport to occur. 



300. Several early papers concerned development of criteria for 

 predicting the predominant direction of the transport (onshore or offshore). 

 Rector (1954) used deepwater wave steepness and ratio between median grain 

 size and deepwater wavelength. Ippen and Eagleson (1955) studied the movement 

 of individual particles on a plane slope under shoaling waves and found net 

 motion to result from inequality of hydrodynamic drag and particle weight. 

 Their criterion for distinguishing between onshore and offshore motion 

 contained three nondimensional parameters: wave steepness, ratio of wave 

 height and water depth, and ratio of sediment fall speed and wave celerity. 



301. Van Hijum (1975, 1977) determined the distribution of the cross- 

 shore transport rate on a beach of coarse material by comparing consecutive 



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