speed of 0.05 cm/sec was used. The results at 0.5 m depth at the end 

 of one-day simulation are shown in Figures 12, 13 and 14. It is clear 

 that resuspension of sediment plays a dominant role in redistributing 

 sediment. The difference in results for (2) and (3) reflects the 

 importance of quantifying the time history of bottom sediments, which 

 strongly affects the erodability as shown in Fig. 11. 



BOTTOM BOUNDARY LAYER AND WAVE EFFECT ON SEDIMENT RESUSPENSION 



The wave climate during the September period of 1980 was studied 

 by means of a spectral wave hindcasting model modified for shallow 

 water. The blockage effect of the barrier islands allows us to assume 

 that most of the wave energy in the Mississippi Sound was derived from 

 the wind fetch within the Sound. From 20 to 2 5 Sept., wind was 

 generally from the Southeast at about 5 m/sec. Results of the wave 

 model indicate wave height generally under 30 cm and wave period under 

 3 sec. At a station off Gulfport (Station 17), the wave-induced bottom 

 stress was the highest among all stations and on the order of 5 

 dyne/cm^ during the first day (Fig. 15a). However, wave-induced stress 

 over most of the sound was generally not wery strong, as can be seen in 

 Fig. 15b, the bottom stress at a station off the Biloxi channel 

 (Station 10) was generally less than 1.3 dyne/cm^. These findings are 

 consistent with the sediment concentration data collected during this 

 time period, which showed a slight initial increase in concentration 

 followed by primarily depositional events. We also found that linear 

 wave theory and empirical bottom stress formula tend to overestimate 

 the wave- induced bottom stress within an oscillatory boundary layer. 



5 m 



Figure 



(o) Station 17 



Off Gulfport. MS 



o 



• 



ao. 



TIME 



eo. so. too. 



tzc 



15 









(b) Stotion 10 



Off Biloxi Channel. MS 



- 



10 



- 









- 



5 



- 









- 





^ 



^V-,n. 



N — r\ 



. r-\ . A^ AA . 



Jl 



IMeURS) 



15. Wave-Induced Bottom Stress at two Locations in the 

 Mississippi Sound from 20 to 25 Sept., 1980. 

 (a). Station 17 off Gulfport, MS. 

 (b) . Station 10 off Biloxi Channel. 



286 



Sheng 



