experiments, was 0.27 millimeter (1.92 pM) (see Vol. I). Some gravel was 

 removed from the sediment before the 1971 experiments. Therefore, the ini- 

 tial sediment-size distribution for the 1970 experiments was greater than 

 0.27 millimeter by an unknown amount. 



Data from experiment 70X-06 at 150 hours and from experiment 70X-10 at 

 200 hours are given in Table 11. The median grain size on the foreshore 

 was generally 0.35 millimeter. At the toe of the foreshore (elevation- 

 -0.2 foot), the median grain size was 0.38 millimeter or greater. The 

 median grain size decreased in the offshore direction to 0.22 millimeter 

 in the offshore zone. 



4. Breaker Characteristics. 



a. Breaker Position with Time and Depth . Data collection and reduc- 

 tion procedures for breaker characteristics are discussed in the Appendix. 

 A plot of breaker position superimposed on a plot of contour movement alon^ 

 range 3 for experiment 70X-06 is shown in Figure 34. During the initial 



32 hours of testing the wave broke at a depth of approximately 0,5 foot 

 (between stations 3.5 and 5.0). From 32 to 42 hours the breaker position 

 moved from station 4.0 to 6.5. This shift in breaker position occurred 

 after the shelf in the outer region of the inshore zone began to develop. 

 From 42 to 78 hours the breaker position continued to move offshore as the 

 seaward edge of the inshore zone moved seaward. From 98 hours until the 

 end of the test the wave broke at a depth of 0.7 foot. 



A similar plot of breaker position superimposed on a plot of contour 

 movement with time for experiment 70X-10 is shown in Figure 35. During 

 the first 40 hours the wave broke between stations 4.0 and 5.5, at a depth 

 of 0.4 to 0.5 foot. Up to 12 hours the wave, broke uniformly across the 

 tank; after 12 hours the wave broke first along range 1. After 40 hours 

 the breaker position gradually moved seaward as the outer edge of the in- 

 shore zone moved seaward. The inshore zone formed more gradually in the 

 10-foot tank and there were no rapid changes in the breaker position. 

 From 40 to 86 hours the wave broke at a depth of 0.6 foot and after 86 

 hours at a depth of 0.7 foot. However, the important distinction is that 

 the breaker position did not occur at the seawardmost position of the 

 -0.7-foot contour intercept as in the 6-foot tank. 



b. Breaker Type with Position, Time, and Depth . Up to 40 hours the 

 breaker in experiment 70X-06 was a plunging-type breaker. Between 40 and 

 45 hours the breaker type changed from plunging to spilling and then 

 remained a spilling-type breaker until the end of the experiment. The 

 change in breaker type occurred as the breaker position moved offshore to 

 a depth of 0.6 foot. Similarly, in experiment 70X-10, the breaker type 

 changed from plunging to spilling as the breaker position moved to a depth 

 of 0.6 foot. 



5. Water Temperature . 



Figure 36 gives data on daily average water temperature versus time 

 for experiments 70X-06 and 70X-10. Since water temperature was not 



65 



