Across profile 



sediment distribution trend 



43. To summarize, the spatial across-profile sediment grain-size dis- 

 tribution varies mainly due to the variation in sediment transport forcing 

 functions and mechanisms. The dune group's principal distribution is related 

 to the coarse lag deposit and bed load and saltation of fine sand sizes due to 

 wind. 



44. The beach group's high variation in grain- size distributions is 

 related to the variation in wind transport on the dry beach and the swash 

 transport processes on the foreshore. The swash transport contains the highly 

 turbulent uprush, which transports sediment upslope on the foreshore in a 

 series of modes, changing irregularly from one of suspension, to saltation, 

 and finally bed load until the forward momentum is stopped by slope friction 

 and gravity (Waddell 1976) . As the bore reaches its maximum runup position, 

 there is a period of decreasing upslope movement. The fluid comes to a momen- 

 tary halt, depositing specific grain sizes caught in the upslope transport. 

 The initiation of backwash begins with a rapid drop in water depth as the 

 fluid accelerates back downslope (Stauble 1979) . The backwash has different 

 internal flow characteristics , with a reverse spectrum of sediment transport 

 modes from bed load through saltation to suspension. The lower backwash 

 obtains high velocities, but shallow depths limit transport capacity. 



45. The bar/trough region is characterized by the breaker and surf 

 zone, where sediment is suspended by the breakers over the bar crest and again 

 at the lower foreshore step. The mechanisms of wave breaking and resulting 

 profile modifications are discussed by Miller (1976) . The surf zone between 

 the bar and the shore transports sediment as the bore travels into shore and 

 interacts with the swash zone (Brenninkmeyer 1976) . 



46. A comparison of the temporal and spatial changes in cross-shore 

 sediment distribution for a winter higher wave period is shown in Figure 21. 

 Sediment grain-size distributions across a well-developed inner bar profile 

 during 2 October 1984 demonstrate the coarse sediment component found in the 

 beach and bar/trough groups . A representative profile from the accretionary 

 period toward the end of the study is shown in Figure 22. Sediment grain-size 

 distributions across a shallow inner bar profile collected during 21 August 

 1985 show an overall decrease in coarse sediment on the profile and the shift 



55 



