94 



Scope of study 



The offshore sand-tracer experiments undertaken during SUPERTANK 

 compliment and extend those made by Miller and Komar (1979) in the same 

 wave channel located at the O. H. Hinsdale Wave Research Laboratory at 

 Oregon State University (OSU). That earlier study was limited to monochro- 

 matic waves with periods of 3, 4, and 5 sec, and offshore wave heights in the 

 range of 15.9 to 37.6 cm. In addition to providing new data with 

 monochromatic waves, some SUPERTANK tracer experiments were 

 undertaken with random waves. Furthermore, the wave energy levels were 

 considerably higher than in the study of Miller and Komar (1979). That 

 earlier study yielded only measurements of sand diffusion under different 

 wave conditions, as there were no significant displacements of tracer that 

 could be interpreted to represent net advection. The rates of diffusion, the 

 "mass spreading coefficients" (Miller and Komar 1979), were quantitatively 

 related to an assessment of the rate of entrainment based on the wave orbital 

 motions following the approach of Madsen and Grant (1976) and to a random- 

 walk model of grain movement that yielded a relationship to d 2 /T, where d is 

 near-bottom wave orbital diameter, and T is wave period. There was some 

 uncertainty as to the correspondence between the wave-channel data with 

 monochromatic waves versus two measurements obtained under higher-energy 

 field conditions. The scope of the offshore SUPERTANK sand-tracer 

 measurements is such that analyses of the data may resolve questions as to 

 how to relate data on sand movements obtained with monochromatic waves to 

 that obtained under random waves, as well as providing quality data at higher 

 wave-energy levels. 



The surf zone tracer experiments were conducted to provide information 

 for supplementing the beach profile survey measurements (see Chapter 2). 

 These qualitative tracer experiments were designed to address such questions 

 as where material originates that forms the break-point bar and how the over- 

 wash process takes place. 



Experiment Technique 



The development of a sand tracer involves tagging the natural sediment 

 with a coating of fluorescent dye that does not alter the hydrodynamic prop- 

 erties of the grains or the overall distribution of sizes as found in the environ- 

 ment to be studied. Teleki (1966), Yasso (1966), and Ingle (1966) provide 

 summaries of the techniques involved in tagging the sand, but the approaches 

 are complex and messy, especially for large samples. The tracers employed at 

 SUPERTANK were dyed professionally by the Great American Color Com- 

 pany in Los Angeles. Large splits of the natural quartz-feldspar sand used at 

 SUPERTANK were trucked to Los Angeles for coating with fluorescent dye. 

 Separate quantities of sand were dyed with five colors: red, green, blue, 

 yellow, and maroon. Availability of several colors was important so they 

 could be used successively and distinguished from tracer introduced in previ- 



Chapter 5 Tracer Measurements of Sand Dispersion 



