calculations of the parameter were made at different water depths in the offshore region. These calculated 

 values, along with ratios of Xie's parameter between prototype and model for tests T03 and T04, are shown 

 in Table 4. The maximum bottom velocity, Umax, was determined from the linear theory relationship 



_ .Hjl + K.) 



where 



H = wave height 



Kr = reflection coefficient 



T = wave period 



h = water depth 



L = local wave length 



114. Reflection coefficients were measured in the model experiment to be about 0.5 at the nearshore 

 gage position, and it was cissumed that prototype reflection coefficients were similar. Critical velocity for 

 sediment motion, [/«, was calculated using the relationship of Hallermeier (1980) given by 



[ttt 



where 



d^o = median grain size 



7/ = immersed specific weight of sediment (about 1.65 for sand) 



g = gravitational acceleration 



Sediment fall speed of the prototype and model sediment are given in Table 1. 



115. The model values of Xie's parameter in Table 4 were calculated using the model depth equivalent 

 to the prototype depth listed in the table. Columns 5 and 6 in Table 4 present the ratio of Xie's parameter 

 in the prototype to that of the model. For test T03, this ratio is always greater than one, approaching 

 unity as the depth decreases. However, the ratio for test T04 is nearer to unity over the range of offshore 

 depths, and quite by accident, appears to be a reasonable compromise over the extent of the offshore 

 portion of the profile. 



116. The better comparison to prototype shown by test T04 suggests a modification to the selected 

 modeling criteria that includes a procedure for adjusting the scaled model wave height in such a manner as 

 to achieve better similarity of Xie's parameter in the offshore regions of the modeled regime. This 

 adjustment is dependent upon the wave period and should probably be limited to the more dynamically 

 active portion of the offshore profile rather than being extended to full depth of closure. 



47 



