After 70 hours, the current pattern began to disintegrate and become 
quite confused. Between 70 and 75 hours, only 67 percent of the bobs 
which moved seaward from station +5 returned; the other 33 percent moved 
past station +16. Between 75 and 80 hours, 33 percent of the bobs return- 
ed, between 80 and 85 hours, 25 percent returned, and between 125 and 130 
hours only 20 percent returned. 
Flourescein dye was introduced on either side of the antinode near 
station 18 and in all cases (all before 70 hours) the dye moved away from 
the antinode and did not diffuse across this boundary. 
b. Experiment 72A-10. A few observations of currents were made in 
this experiment during the first 30 hours and no repeatable current 
pattern was observed. There was never any indication that a pronounced 
current pattern existed during the experiment. 
III. PROFILE DEVELOPMENT AND REFLECTIVITY 
This section discusses the interdependence of changes in profile shape, 
sediment-size distribution, breaker characteristics, current patterns, 
water temperature, and the reflection coefficient. 
1. Experiment 72A-06. 
Profile development is summarized in Table 12 which tabulates, as a 
function of time, the important changes in the foreshore and offshore 
zones, the breaker and current conditions, median grain size, and water 
temperature during this experiment. Figure 40 compares the shoreline 
movement with water temperature changes for experiment 72A-06; Figure 41 
compares the -1.2-foot contour movement, which represents the boundary 
between the inner and outer offshore regions with Kp changes. 
The important changes in the various parameters and their inter- 
relationships occurred as follows. In the first 5 hours the foreshore 
developed an equilibrium shape, which was steep along range 5 and quite 
flat along range 1 as a result of the counterclockwise pattern of flow 
of the wave uprush and backwash. Since the waves broke on the foreshore, 
it received most of the wave energy, and as the foreshore became steeper 
the Kp increased, except at 1.5 and 3,hours. At those times, the 
erosion and deposition patterns at the base of the foreshore (-0.2 to 
-0.9 foot) were reversed and the Kp reached its lowest values. 
An almost flat shelf developed during the first 10 hours in the inner 
offshore region, caused by the erosion at the toe of the foreshore and 
deposition in the outer offshore at depths from -1.3 to -1.6 feet. As the 
foreshore eroded landward at a rate of 0.015 foot per hour and the outer 
offshore slope steepened and prograded seaward with deposition at the 
higher elevations, the shelf in the inner offshore grew in length in both 
directions and a bar and trough developed. During this period of greatest 
profile development the Kp rose sharply, reaching a maximum at 25 hours. 
As a result of the high reflection, a significantty large standing wave 
70 
