in the mean median size on the foreshore at 300 and 375 hours could have 

 been the result of the profile eroding into the relict profile from 1970, 

 which had coarser material. The median grain size in the inshore zone 

 was 0,2 7 millimeter or greater for the first 300 hours and at 375 hours 

 a few samples had a djg lower than 0.27 millimeter; the median grain 

 size in the offshore zone was as low as 0o23 millimeter. As expected, 

 more of the finer material eroded from the foreshore (raising the dso 

 in that zone) and deposited in the offshore (lowering the d^Q in that 

 zone) . The material deposited on the foreshore by the long-period wave 

 was finer material, thus significantly lowering the dso on the fore- 

 shore at 380 hours. 



b. Experiment 71Y-10 . A similar summary of median grain-size data 

 for experiment 71Y-10 is given in Table 12. The same trend in median 

 grain-size changes occurred, but was even more distinct. With one ex- 

 ception, the median grain size in the foreshore zone remained above 0.27 

 millimeter. The increase in the mean median size in the foreshore zone 

 could have been the erosion into the relict profile. In the offshore, 

 dso varied only between 0,24 and 0.29 millimeter. 



4. Breaker Characteristics . 



a. Experiment 71Y-06 . Breaker position superimposed on contour move- 

 ment along range 3 is shown in Figure 37 for experiment 71Y-06. During 

 the first 180 hours the wave broke mostly at a depth of 0.6 foot, breaking 

 by plunging for the first 105 hours and by plunging and spilling for the 

 next 75 hours. After 180 hours the breaker position coincided with the 

 general seaward movement of the -0.7- foot contour, and the breaker type 

 was primarily spilling. Between 220 and 315 hours the wave broke twice-- 

 by spilling at a depth of 0.7 foot and by plunging at the toe of the fore- 

 shore. 



Between 375 and 380 hours the 3. 75-second wave was a surging-type 

 breaker on the foreshore. 



b. Experiment 71Y-10 . Breaker position superimposed on contour move- 

 ment along range 5 is shown in Figure 38 for experiment 71Y-10. The wave 

 broke by plunging at a depth of 0.6 foot for the first 125 hours with no 

 lateral variation in the breaker position. From 125 to 265 hours the wave 

 type varied between plunging and spilling, and the breaker position varied 

 from stations 8 to 10 along range 9 (breaker depth about 0.7 foot), and 

 from stations 5 to 7 along range 1 (breaker depth about 0.6 foot). 



From 265 to 280 hours the breaker type was spilling and the breaker 

 position along range 9 remained at about station 9. Along range 1, the 

 breaker position moved to station +2 at 270 hours and -2 at 275 and 280 

 hours . 



The most significant change occurred between 280 and 285 hours. Be- 

 tween range 10 (station 8) and range 3 (station 2) the wave broke by spill- 

 ing; between range 3 and range the wave broke by plunging at station -2 



79 



