the shoreline toward the seawardmost point of the shoreline (generally 
flowing from range 1 to 7 or from range 9 to 3). The direction of the 
longshore current shifted as the backshore on different sides of the 
tank eroded. 
No observations were made of the surface currents between 35 and 85 
hours. After 85 hours the longshore current was observed, but the cir- 
culation pattern between the shoreline and the breaker zone was more 
confused. Strong seaward currents were observed at times along the tank 
walls from the shoreline through the breaker zone. 
b. Bottom Currents. During the first 95 hours, concentrations of 
organic debris, such as leaves and twigs, were observed in the area 
where the seaward current met the breaker line. The debris did not move 
across the tank through the breaker zone as the surface currents did. 
However, when the longshore current changed direction and the seaward 
current shifted to the other side of the tank, the debris also moved to 
the other side of the tank. 
After 85 hours, circular currents were observed between stations -6 
and +8 (Fig. 24). From 87 to 91 hours the pattern was a single counter- 
clockwise circular cell (Fig. 14,a); from 92 to 108 hours, two circular 
patterns existed (Fig. 24,b). Between 108 to 140 hours, a single cell 
again occurred in the clockwise direction (Fig. 24,c), except between 
110 and 111 hours when the direction reversed (as in Fig. 24,a), and at 
139 hours when a dual cell developed as shown in Figure 24(d). 
6. Water Temperature. 
Figure 25 gives data on the daily average water temperature versus 
cumulative test time and real time. The water temperature decreased 
throughout 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 
characteristics are related to the variability of the reflection coef- 
ficient. Profile development is discussed first to provide an intro- 
duction 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 
Rabies 
The profile development discussed previously and condensed in Table 
11 occurred as follows. In the first 1.5 hours the plunging breaker 
48 
