1.0 



+ 8609151345 8609181453 



* 8609151630 • 8609201045 



08 _|_ n 8609181225 x 8609201500 



g 0.6 "t- 



I 

 E 



0.4 — 



0.2 



LEGEND 



pqVH (1000 N/m-sec) 

 r ^ rms 



Figure 18. Longshore sand transport rate density versus /f^jV 



best fit from linear regression analysis. Values of the determined regression 

 equation coefficients and the correlation coefficient squared (r 2 ) are listed 

 in Table 6. Figure 18 shows that the measured transport rate densities are 

 fairly well described by a purely linear function of H IIBS V . However, 

 scatter is relatively great, suggesting that the transport rate densities may 

 have a power- law dependence on H^^V , based on the trend of the data. 



45. Qualitative observations made during DUCK85 indicated that the 

 trapped amount of sand depended on the intensity of water agitation occurring 

 at or immediately seaward of a trap. For example, the transport rate appeared 

 to increase in turbulent white water as compared with calmer green water for 

 traps located at approximately the same depth. The white, agitated water was 

 produced by waves breaking at the trap or convected to the trap by waves 

 breaking immediately seaward. The local gradient of the wave height dH^^dx 

 was identified as a readily evaluated measure of water agitation, and the 

 SUPERDUCK TSM runs were configured to provide this quantity. The gradient of 

 wave height was calculated from the nearest two photopoles (i.e., over a 6-m 

 interval). The gradient was usually positive, indicating a decrease in wave 



45 



