(Fig. 39) . This pattern was maintained for the remainder of the experi- 

 ment. During the last 10 hours of this experiment, a strong seaward 

 current was observed in the inshore zone between ranges and 2, in the 

 region where the wave did not break until reaching the toe of the fore- 

 shore. 



Contour maps in Figure 40 show the profile at 135 and 335 hours. 

 Figure 41 shows ripple formations between ranges and 2 and stations 

 +2 to +5, where large ripples are oriented in the seaward direction. A 

 plausible explanation for the breaking pattern and current development 

 is that: (a) As the wave broke first along range 9, energy moved along 

 the wave crest toward this range; (b) this loss of energy along the lower 

 ranges decreased the wave height along the lower ranges causing the waves 

 to break even farther inshore so that eventually the waves along range 2 

 lost enough height (energy) to not break until the waves had traveled 

 farther up the profile; and (c) the flow of energy along the wave crest 

 toward range 9 increased the shoreward mass transport along that side of 

 the tank, and the seaward return flow of mass transport chose the path 

 of least resistance--along range 1. 



5. Water Temperature . 



Figure 42 gives data on daily average water temperature versus both 

 cumulative test time and dates for experiments 71Y-06 and 71Y-10. 



III. 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 distribu- 

 tion, 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 coeffi- 

 cient. Profile development is discussed first to provide an introduction 

 to profile reflectivity. 



1. Profile Development . 



a. Experiment 71Y-06 . The important changes in the foreshore, in- 

 shore, and offshore zones, the breaker conditions, median grain size, and 

 water temperature during experiment 71Y-06 are summarized and tabulated 

 as a function of time in Table 13. 



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. The eroded material during this early development was deposited 

 at elevations -0.6 to -1.2 feet in the first 2 hours. As the foreshore 

 retreated at 0.113 foot (3.44 centimeters) per hour for the first 15 hours 

 and the bar moved shoreward at 0.018 foot per hour, the eroded material 

 was deposited mostly at elevation -0„9 to -1„2 feet up to 10 hours and 

 uniformly at all depths in the offshore zone after 10 hours (see Figs. 7, 

 8, and 9). After 15 hours the shoreline recession rate dropped to 0.025 

 foot per hour. 



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