10 Intermittent Near-Bed 



Sediment Suspension in the 

 Offshore at SUPERTANK 1 



Introduction 



Background 



The processes of wave-seabed interaction are extremely complicated and 

 exhibit nonlinear behavior due to many couplings amongst the flow properties 

 and bed characteristics. An adequate understanding of the physical interac- 

 tions between fluid and grains near the seabed is necessary to develop the 

 capability to model, predict, and control coastal sediment transport and associ- 

 ated bathymetric change. The intermittent suspension of sand by waves is a 

 significant process and the focus of this study. 



Previous observations (Jaffe, Sternberg, and Sallenger 1985; Hanes 1990; 

 Vincent, Hanes, and Bo wen 1991) of sand suspended by waves indicate that 

 fluctuations in suspended sediment concentration are significant. The phase of 

 sediment entrainment and the characteristics of suspension events are related 

 to the direction of time-averaged net cross-shore suspended transport. The 

 importance of intermittent suspension to sediment flux can be demonstrated by 

 considering the various temporal contributions to cross-shore transport of 

 sediment. The time-averaged net cross-shore suspended sediment in wave- 

 dominant regions consists of a fluctuating portion and a steady portion, i.e., 



uc = uc + u'c' ( 10-1 ) 



where 



U = cross-shore component of instantaneous sediment velocity 

 C = instantaneous concentration of suspended sediment 



'Written by Daniel M. Hanes, Tae Hwan Lee, and Eric D. Thosteson, University of Florida. 

 Chapter 10 Intermittent Near-Bed Sediment Suspension 



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