5 Tracer Measurements of 

 Sand Dispersion During 

 SUPERTANK 1 



Introduction 



Background 



There have been considerable advances in recent years in our understand- 

 ing of sediment transport processes in the nearshore and in our ability to 

 predict transport rates under a given set of wave conditions. However, many 

 unknowns remain, in part resulting from the diversity of measurement tech- 

 niques and uncertainties as to how they are related. On the one hand, most 

 data for comparing longshore sand transport rates on beaches to the causative 

 waves and nearshore currents have come from sand-tracer measurements, 

 which permit one to follow immense numbers of grains in an integrated fash- 

 ion. Examples of the use of fluorescent sand tracers to measure longshore 

 sediment transport rates on beaches are provided by the studies of Komar and 

 Inman (1970), Knoth and Nummedal (1977), and Kraus et al. (1982). A re- 

 cent review of the technique and the collected field data is given by Komar 

 (1990). The tracer technique measures the total sediment transport rate, bed 

 load, and suspended load, because all grain sizes represented in the sand are 

 tagged in their natural proportions. 



Sand tracers have also been employed to follow cross-shore sand move- 

 ments and grain sorting across the beach profile (e.g., Ingle 1966), as well as 

 to reveal sediment transport patterns in a qualitative manner in complex en- 

 gineering situations (e.g., Sasaki and Sakuramoto 1984). At the same time, 

 measurements have been made by a number of investigators using arrays of 

 optical backscatter sensors (OBS) to determine suspended-sediment concentra- 

 tions, which, when combined with measurements of currents obtained by 

 electromagnetic current meters, yield assessments of the net suspended sedi- 



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'Written by Paul D. Komar, Oregon State University. 



Chapter 5 Tracer Measurements of Sand Dispersion 



