transition zone moves together with the bar during the course of wave action, 

 which makes analysis problematic, as the transport rate calculations are based 

 on average profile changes that occurred over a relatively long time. 

 However, from a conceptual point of view, it is important to recognize this 

 region as being different from neighboring areas. 



355. Some distributions provided insight into the nature of the net 

 transport rate in Zone II, particularly during later times of a run, when 

 changes in the beach profile shape were more gradual. Figure 48 illustrates 

 the transport rate distribution in the region between the break point and the 

 location of the maximum transport rate for selected cases and times. The 

 transport rate decreased in the offshore direction at a lower rate than in the 

 region seaward of the break point. Analysis of a small data subset where Zone 

 II transport could be distinguished (as in Figure 48) indicated that an 

 exponential decay was a reasonable approximation, with the spatial decay 

 coefficient approximately 0.20-0.25 of the value of the spatial decay coeffic- 

 ient governing transport seaward of the break point. 



Zone III: Net transport rate in broken waves 



356. Breaking and broken waves produce turbulent conditions that put 

 grains into suspension and make them available for transport across the 

 profile (Watts 1953, Fairchild 1973, Kana 1977, Kraus and Dean 1987). Thus, 

 it is plausible to assume that the magnitude of the transport rate is closely 

 related to wave energy dissipation (Dean 1977). Different models of wave 

 height decay in the surf zone based on energy dissipation have been 

 developed (e.g., Dally 1980; Mizuguchi 1981; Svendsen 1984; and Dally, Dean, 

 and Dalrymple 1985a, b) . 



357. The CE data set did not include detailed measurements of the wave 

 height distribution across the profile, whereas the CRIEPI data set provided 

 wave height data for most of the cases with a resolution of 2.5 m. The wave 

 height distribution was usually measured between profile surveys, making the 

 exact beach profile shape unknown for the time of the measurement. To obtain 

 a picture of the relationship between the cross -shore transport rate and local 

 wave parameters in broken wave zones, the CRIEPI data set was used, although 

 the number of cases that contained significant profile change and correspond- 

 ing measurements of wave height across-shore was limited. Only four cases 



146 



