Figure 5-5. Example of offshore bottom with irregular ripples 



Summary 



Fluorescent sand tracers were used during SUPERTANK to measure sand 

 dispersion (advection and diffusion) seaward of the breaker zone. Additional 

 experiments were conducted within the surf zone to document the exchange of 

 sand between the beach face and sandbars. 



Five offshore experiments were completed, including sixteen sampling runs 

 encompassing a wide range of wave conditions. For the most part, the results 

 show the expected diffusion of tracer with time, and often an apparent net 

 onshore advection. Future analyses will be undertaken to calculate average 

 diffusion and advection rates for the experiments, with a comparison of the 

 results to the wave parameters and direct measurements of suspended sediment 

 concentrations. The analyses will expand the range of results reported in the 

 comparable study by Miller and Komar (1979), in that the SUPERTANK data 

 extend to significantly greater wave-energy levels and include measurements 

 under random as well as monochromatic waves. More sophisticated analyses 

 of the offshore sand-tracer dispersion measurements obtained during 

 SUPERTANK could involve the development of a sand dispersion model 

 which utilizes the OBS measurements of the temporal and spatial variation in 

 sediment concentrations, models that would yield a greatly improved under- 

 standing of the processes and patterns of sediment transport under waves. 



Chapter 5 Tracer Measurements of Sand Dispersion 



103 



