between the two reflected wave components to vary. When the components 

 were in phase, the measured H^> (in the constant-depth section) was 

 high; when the components were out of phase, the measured Hn was lower 

 than the absolute sum of the two reflected waves. 



Because the phase difference between the two reflected components 

 varied, the amount of energy reflected from the submerged profile could 

 not be measured. However, the effect of the three profile changes can be 

 seen in the reflection variability of some of the experiments. 



b. Reflection of the 1.50-Second Wave . Figure 2 shows the K^> 

 versus time for experiment 72C-10, the only experiment with a 1.50-second 

 wave period. The K^ varied between 0.02 and 0.12 during the experiment s 

 with no apparent increasing or decreasing trend in the maximum or minimum 

 values or in the amount of variation. Minimum values occurred at 35, 60, 

 90, 95, and 120 hours; maximum values occurred at 1.5, 25, 55, and 105 

 hours. 



Steep foreshore and offshore slopes developed almost immediately and 

 then began to separate as the foreshore eroded landward and the offshore 

 prograded seaward (Table 3) . As the two reflecting zones separated, the 

 change in phase difference between the two reflected waves would have 

 caused a variation in the measured (total) K^. Assuming linear theory 

 and an average depth of 0.6 foot (18.3 centimeters), an increase of 3.12 

 feet (0.95 meter) in the distance between the two reflecting zones (i.e., 

 the width of the inshore) would have caused a 360° change in phase dif- 

 ference. The distance between the 0- and -1.0-foot (0 to 30.5 centi- 

 meters) contour increased from 10 to 28.5 feet (3.0 to 8.7 meters) during 

 the experiment. Therefore, five cycles of 360° phase-difference change 

 were possible and if the cycle started with the two waves 180° out of 

 phase, four in-phase (maximum) values were possible, as observed. The 

 average K^> was 0.05 (Table 2). 



The seaward movement of the seawardmost -0.8-foot (24.4 centimeters) 

 contour (Fig. 2) is an indicator of the general steepening of the off- 

 shore zone and the shoreward movement of this contour that the elevation 

 at the top of the submerged offshore slope dropped to -0.9 foot (27.4 

 centimeters). The shoreward movement of the -0.8-foot contour near the 

 end of the experiment did not cause any noticeable reduction in K„, as 

 was observed for -0.7- foot (21.3 centimeters) contour during tests with 

 the 1.90-second wave (see Fig. 45 in Vol. Ill), but here the average K„ 

 was already smaller than the 1.90-second wave. 



c. Reflection of the 1.90-Second Wave . 



(1) Experiment 70X-06 . The reflection coefficient, K^>, 

 versus time for experiment 70X-06 is shown in Figure 3. During the first 

 10 hours, K^ varied between 0.03 and 0.14. At 10 to 25 hours, K^ 

 remained fairly constant (0.08 to 0.11) and then dropped to 0.02 at 31 

 hours. From 33 to 45 hours, the K^ was lower, between 0.04 and 0.08, 



