if the depth difference is an appreciable fraction of the average depth 

 over a horizontal distance less than a wavelength. For the conditions 

 of this experiment, the wavelength is 14.3 feet (4.36 meters) in the 

 section seaward of the movable bed and approximately 9 feet (2.74 meters) 

 over the inshore zone. The depth change over the inshore zone is about 

 1 foot at the deepest section, and occurs over about 8 feet in the hori- 

 zontal (Fig. 7) . 



a. Reflection from the Foreshore . The foreshore zone did not develop 

 until 5 hours (Fig. 10) . The developed foreshore had a slope of about 

 0.19, considerably steeper than the original 0.05 slope. The rise of 



% above 0.06 after 1.5 hours (minimum point in Fig. 3) may be the 

 result of the formation of the foreshore. 



K^ measurements over the inshore shelf after 100 hours (Table 7) 

 indicated that reflection from the foreshore varied from 0.06 to 0.12 and 

 was not as variable as the total Kd values. 



b. Reflection as a Result of Wave Breaking . The plunging breaker 

 and the longshore bar developed almost immediately and were probably the 

 largest reflectors during the first 3 hours when no other features were 

 prominent on the profile (Figs. 3 and 3). The K^ during the first 3 

 hours was only 0.06 or less, so the breaker could only have contributed 

 that much or less. By 20 hours the breaker type was already mixed be- 

 tween plunging and spilling. Reflection from a spilling breaker is as- 

 sumed to be negligible, so that after 20 hours the reflection from the 

 breaker would have become small and after 100 hours the reflection from 

 the primary breaker would have been negligible. Reflection from the 

 secondary breaker, after 100 hours, would also have been small, because 

 the wave height at that point was much smaller. Thus, reflection from 

 the breaker was probably never very important, and became less important 

 as the breaker type changed. 



c. Effect of Inshore and Offshore . As the shelf in the inshore zone 

 developed after 5 hours, the offshore slope became slightly steeper and 

 the K^ increased significantly. As the shelf widened, the K^ decreased 

 for a time and then increased to a maximum value during the period of 

 greatest deposition at the outer edge of the inshore shelf and the upper 

 offshore slope. Subsequently, as the shelf widened more, the K^ de- 

 creased (Figs. 3 and 8). 



With the development of the two reflecting zones (foreshore and off- 

 shore) separated by a relatively flat inshore zone, the measured re- 

 flected wave was composed of two reflected waves. A change in phase or 

 amplitude of either reflected wave would change the phase and amplitude 

 of the measured wave. Part of the Kn variability can be attributed to 

 the change in phase difference between these two reflected waves as the 

 foreshore retreated landward and the offshore built seaward. 



48 



