from runs 21 to 43, and, during this time, suspended sediment concentration 

 data were still accurately collected from the other OBS and the ACP. Flow 

 velocity data from the second week were inaccurate due to a malfunction of 

 the EMCM. This malfunction occurred from runs 40 to 83. Velocity data 

 could be derived from pressure sensor data or could be obtained from other 

 investigators in the area. 



Examination of the return signal from the ACP revealed the presence of 

 the OBS in the path of the acoustic beam. Because the OBS were at fixed 

 locations, acoustic signals were affected identically with each profile, the 

 presence of the OBS in the profile is not significant, and the effect was 

 eliminated from almost all the concentration profiles in the calibration as 

 explained in the summary of data characteristics. This presence can be seen 

 in the raw data from runs 1 to 62. 



Summary 



Review of experiments and results 



The information provided in this chapter represents a fairly thorough 

 description of the hydrodynamics and resulting sediment dynamics in a single 

 location in the offshore region of the channel. The large fluctuation of 

 measured values over short periods of time in this region suggests the timing 

 of individual suspension events may be an important contribution to the 

 resulting sediment transport. Variations in sediment concentration with height 

 from the bed appear to be significant, and inspection of data from the OBS 

 and the ACP verifies that these fluctuations can be measured with high spatial 

 and temporal resolution. This knowledge will aid in describing the small- 

 scale processes, which will in turn reveal the importance of these processes in 

 modeling large-scale bathymetric changes. At times, other investigators 

 simultaneously collected data with instrumentation positioned at the same 

 location in the offshore region. Examination of additional data from these 

 other investigators can further enhance the value of this data set. 



Recommendations 



Although this data set is fairly complete, its usefulness is limited due to 

 several factors. The most obvious limiting factor was in the use of a 

 laboratory channel. Because the waves were prototype scale, agreement with 

 field measurements is probably close, but the ideal unidirectionality of the 

 waves, the near ideal bathymetry, and other obvious discrepancies with an 

 actual field site are sure to cause some differences. In March of 1992, a field 

 experiment was conducted at Vilano Beach, FL, with the same 

 instrumentation. The present analysis of the data from the field experiment 

 should provide the necessary data to form a comparison between the lab and 



Chapter 10 Intermittent Near-Bed Sediment Suspension 



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