measured before 13 July 1970, no data are available from to 38 hours in 

 experiment 70X-10. 



Ill, PROFILE DEVELOPMENT AND REFLECTIVITY 



Results are analyzed by (a) profile development, in which the inter- 

 dependence of the changes in the profile shape, sediment-size distribution, 

 breaker characteristics, and water temperature is analyzed; and (b) profile 

 reflectivity, in which changes in profile shape and breaker characteristics 

 are related to the variability of the reflection coefficient. Profile 

 development is discussed first to provide an introduction to profile reflec- 

 tivity. 



1. Profile Development . 



a. Experiment 7QX-06 . Important changes in the foreshore, inshore, 

 and offshore zones, the breaker conditions, and water temperatures are sum- 

 marized in Table 12. The daily mean water temperature and the shoreline 

 position are compared in Figure 37. 



During the first hour, the foreshore zone developed the basic 

 shape which was maintained throughout the remainder of the experiment , and 

 a longshore bar was formed by the plunging breaker in the inner inshore 

 region. During the first 22 hours the foreshore retreated at an average 

 of 0.06 foot per hour, while the water temperature was near 28° Celsius. 

 Most of the eroded material was deposited at depths greater than 1.1 feet 

 during the first 5 hours and greater than 0.8 foot between 5 and 22 hours. 



From 22 to 30 hours the foreshore retreated considerably faster (an 

 average of 0.14 foot per hour) coincidental with a temperature drop of 

 10° Celsius (see Fig, 37). This increased erosion created a much wider 

 inner region in the inshore zone and most of the eroded material was 

 deposited between 22 and 26 hours at depths of 0.7 and 0,8 foot, forming 

 the flat shelf in the outer region of the inshore zone and the relatively 

 steep slope in the offshore zone. After 26 hours the material was deposited 

 at a depth of 0.8 foot, the seaward edge of the inshore. 



From 30 to 44 hours the shoreline retreat and the stability of the 

 bar created a wider inner region of the inshore zone. The breaker began 

 moving seaward, breaking at a depth of 0.6 foot, and after 40 hours, 

 changed from plunging to spilling. 



After 44 hours the position of the foreshore stabilized and the shelf 

 in the outer region of the inshore zone began to widen as sediment was 

 eroded at depths of 0.5 and 0.6 foot. The beach had eroded to the back of 

 the tank at 54 hours and sand replenishment began at that time. After 54 

 hours the bar in the inner region of the inshore zone began to disappear, 

 and the breaker moved seaward, breaking at a depth of 0.7 foot. The outer 

 region continued to extend seaward as material eroded from the backshore 

 was deposited on the steep offshore slope. After 66 hours the shape of 

 the inner inshore became stable, 



70 



