judged that the water sampler analysis was probably conducted with the surface 

 samples and the bottom samples reversed. The resulting surface and bottom 

 concentrations on 9/2/80 are then interpolated onto our numerical grid and are 

 shown in Figure 7.25. Surface concentrations are on the order of 20 mg/1 

 while bottom concentrations are on the order of 70 mg/1. 



Several days later, on 9/8/80, another survey was carried out in the 

 western sound. On 9/9/80, the survey proceeded from the Ship Island to the 

 Pascagoula Channel. On 9/10/80, the remaining stations in the eastern Sound 

 were surveyed. The resulting concentration measurements are interpolated onto 

 our grid and are shown in Figure 7.26. It is apparent that both the surface 

 and the bottom concentrations have decreased slightly from those obtained on 

 9/2/80. 



Model Simulation 



Using the model computed bottom stresses and the deposition and 

 entrainment relationship derived from laboratory experiments, we have computed 

 the time variation of the suspended sediment concentration within the bottom 



1 m at several stations. 



Initially, the suspended sediment concentration was assumed to be zero. 

 Relatively calm weather conditions prior to the steady period indicates the 

 bottom sediments are fairly compacted during the initial period. Entrainment 

 relationship corresponding to a 5-day settling time is used in the 

 calculation. The results at stations 8, 10, and 17 are shown in Figure 7.27. 



From the results, it is apparent that the high wave-induced bottom 

 stresses have led to entrainment during 9/3/80 to 9/7/80. From then on, 

 however, wind speeds decreased substantially and wind directions changed from 

 the strong easterlies to the weak northerlies which had very short fetches and 

 little wave energies. Deposition thus prevailed over most of the Sound to 

 yield the low concentration distribution on 9/8/80 and 9/9/80. The 

 near-bottom concentration at stations 8 and 17 are on the order of 100 mg/1 on 



2 September, and on the order of 40 mg/1 on 8 September. All of the model 

 simulated results agree quite well with the available ship survey data at the 

 end of the simulation period (indicated by the circles in Figure 7.27). It is 



201 



