Table 5-2 



Foreshore and Surf Zone Sand Tracer Experiments During 



SUPERTANK 



Date 



Color 



Weight 

 lb (kg) 



Run 



Location 

 of Injection 

 by Color 



5 Aug 



Green 



Red 



Blue 



1 .0 (0.45) 



1.0 



1.0 



09A 



Station 3.5 

 Station 3.9 

 Station 4.4 



5 Aug 



Green 



Red 

 Blue 



1.0 (0.45) 



1.0 

 1.0 



10A 



Station 8 (bar 



trough) 



Station 10 (on bar) 



Station 1 2 (offshore) 



8 Aug 



Blue 

 Orange 



10.0 (4.5) 

 10.0 



12A 



Seaward end of 



berm 



Shoreward end of 



berm 



26 Aug 



Blue 

 Orange 



4.7(2.1) 

 4.7 



12B 

 17B 



In front of seawall 

 In front of seawall 



28 Aug 



Blue 



8.5 (3.9) 



09B 



Station + 9 

 (on berm) 



28 Aug 



Red 



Blue 



2.0 (0.9) 

 2.0 



16B 



Top of foredune 

 Shoreward toe of 

 foredune 



This distribution is typical in showing an onshore movement of tracer, with 

 the maximum concentration displaced toward the beach 0.5 to 1 m from the 

 injection position. The distribution is strongly asymmetrical, with higher con- 

 centrations onshore of the maximum concentration, as compared with offshore 

 positions. The asymmetry suggests a non-uniformity in the rate of diffusion 

 along the length of the wave channel, as well as the injected tracer acting as a 

 quasi-continuous source rather than being an "instantaneous" injection (quasi- 

 continuous source behavior was also found by Miller and Komar (1979)). 



The patterns of measured concentrations seen in the histograms of Fig- 

 ure 5-4 show that the variations are not smooth and systematic, but instead 

 "jump," with adjacent grid samples yielding significantly different concentra- 

 tions. In future analyses of the measurements, it will likely be necessary to 

 smooth the results or to match analytical grain-dispersion equations to yield 

 minimum-error fits to the data. The cause of the concentration variability is 

 uncertain. One possibility is that it represents sampling effects, with perhaps 

 some vials having reached into the bed and sampled sediments having lower 

 concentrations. Another possibility is that the concentration variability reflects 

 the irregular bottom topography with areas of scour and fill. While undertak- 

 ing sampling operations, the diver noted that during most experiments there 

 was large-scale waviness in the bed and localized scour holes, as well as 

 small-scale vortex ripples. In view of this three-dimensionality of the ob- 

 served bottom topography, such as shown in Figure 5-5, the author's mea- 



Chapter 5 Tracer Measurements of Sand Dispersion 



99 



