flow. Sorting of material is thus expected along the profile, with coarser 

 material migrating closer to shore (Ippen and Eagleson 1955). 



342. Erosional cases . For erosional profiles, in the vicinity of the 

 break point it is expected that diffusion in the seaward direction of sand 

 that was set in suspension by the breaking waves dominates over material moved 

 along the bottom by oscillatory wave forces. As seen from Figure 33, the 

 shape of the net transport rate distribution is well approximated by an 

 exponential decay with distance from a point somewhat seaward of the location 

 of the maximum transport rate. This point is located in the vicinity of the 

 break point, and the transport rate q in Zone I may accordingly be written 



^^^-A(x - xj,) ^21) 



where 



qjj = transport rate at the break point 

 A = spatial decay coefficient 

 Xj, = location of breakpoint 



343. In analysis of the distribution of the net transport rate seaward 

 of the break point, cases involving mainly onshore transport and offshore 

 transport were studied separately. Equation 21 was least-squares fitted 

 through the data for 12 cases showing mainly erosion and for 13 cases showing 

 mainly accretion. Each case typically comprised 5-10 transport rate distri- 

 butions for which a spatial decay coefficient was obtained. For a specific 

 transport rate distribution a high coefficient of determination was always 

 obtained (above 90 percent) . The estimated decay coefficient A was quite 

 stable and showed only a slight tendency to decrease with time. Figure 44 

 illustrates the spatial decay coefficient as a function of time for four of 

 the erosional CE cases . 



344. To obtain an overall estimate of the spatial decay coefficient for 

 a specific erosional case, the transport rate for each distribution during a 

 run was normalized with the q^-parameter as given by the least-squares fit for 

 the individual distribution. Figure 45 illustrates, for CE Case 500, the 

 decay of the normalized transport rate from the break point and seaward for 

 consecutive transport rate distributions (indicated by various symbols) 



140 



