7 Sediment Suspension Mea- 

 surements from a Mobile 

 Platform at SUPERTAIMK 1 



Introduction 



Background 



A fundamental feature of the surf zone that is obvious to even the casual 

 observer is the suspension of sand by breaking waves. In following a single 

 wave as it crosses the nearshore, the pattern of suspended sand left behind 

 often resembles bands of clouds that stretch along the shore. Usually, sand 

 concentrations are at their greatest in the zone of initial wave breaking, 

 especially if the breakers are plunging (Kana 1979; Kennedy, Erlich, and 

 Kana 1981), and a well-defined boundary between regions of high and low 

 turbidity is evident just seaward of breaking. In addition to the zone of initial 

 breaking, if wave re-forming is prevalent, a second "suspension boundary" 

 can be found near the toe of the swash. Strong cross-shore gradients in mean 

 suspended load exist in these zones, so the potential for strong gradients in 

 mean transport also exists. Gradients in mean transport lead to the creation of 

 depositional and erosional features, such as the swash step and the longshore 

 bar and trough. Because the sediment is also carried by the longshore 

 current, the location and intensity of these peaks in suspension are also of 

 paramount importance in longshore transport processes. In short, it is clear 

 that basic measurement and modeling of sand suspension across the entire surf 

 zone, with particular emphasis on the regions where suspension is greatest, is 

 a key element in the development of process-based formulas for coastal 

 sediment transport, as well as improved beach evolution models. 



The measurement technology available to study suspended sediment in the 

 surf zone can be divided into two categories: (a) direct physical sampling and 

 (b) inference based on radiation scattering. Suction sampling (e.g., Watts 

 1953; Fairchild 1974; Coakley et al. 1978; Nielsen, Green, and Coffey 1982), 



'Written by Stephen F. Barkaszi and William R. Dally, Florida Institute of Technology. 

 Chapter 7 Sediment Suspension Measurements from a Platform 



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