Breaker height was determined twice during the experiment. At 30 

 hours the breaker height was 0.49 foot (14.9 centimeters) and the breaker 

 depth was 0.65 foot (19.8 centimeters); at 80 hours the breaker height 

 was 0.58 foot (17.7 centimeters) and the breaker depth was 0.70 foot. 



5. Wave-Generated Currents . 



The procedures for collecting current velocity data are described in 

 Volume I. During the first 50 hours of this experiment, observations of 

 the wave-generated currents were made using small bobs. Regular observa- 

 tions of the bottom currents were not possible, but on three occasions 

 the heavy bobs were recovered several feet seaward of their initial 

 placement, indicating a seaward current near the bottom. 



The surface currents in the inshore zone were all in the shoreward 

 direction, and at times the currents tended to move from the center of 

 the tank toward the range 1 side of the tank before 40 hours and toward 

 the range 9 side after 40 hours. On three occasions, surface bobs near 

 the toe of the foreshore moved in a circular pattern. 



6. Water Temperature . 



Figure 19 gives data on the daily average water temperature versus 

 cumulative test time and real time. The water temperature generally 

 decreased during the experiment. 



III. PROFILE DEVELOPMENT AND REFLECTIVITY 



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

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

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

 profile reflectivity, in which changes in profile shape and breaker char- 

 acteristics are related to the variability of the reflection coefficient. 

 Profile development is discussed first to provide an introduction to 

 profile reflectivity. 



1 . Profile Development . 



The important changes in the foreshore, inshore, and offshore zones, 

 the breaker conditions, median grain size, and water temperature during 

 this experiment are summarized and tabulated as a function of time in 

 Table 11. 



Almost immediately the plunging breaker formed a longshore bar on the 

 inner inshore, which eroded between 3 and 5 hours. During the first 5 

 hours the foreshore developed and material was deposited at depths of 

 0.6 to 0.9 foot. 



Between 5 and 125 hours the shoreline retreated at a fairly constant 

 rate of 0.05 foot per hour. The inner inshore eroded to a fairly steep 



43 



