of 0.24 to 0.18, then to 0.17 at 3 hours, and then began to increase, 

 reaching 0.30 at 25 hours. Between 25 and 80 hours, K^ remained high, 

 fluctuating between 0.25 and 0.31. After 80 hours, K^ started to 

 decrease while continuing to fluctuate, and was 0.22 at the end of the 

 experiment (135 hours). 



Within 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 flow pattern of the wave uprush and backwash (Table 

 11; Vol. VI). Since the waves broke on the foreshore, most of the wave 

 energy reached the foreshore; as the foreshore became steeper, K^ in- 

 creased, 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 or 

 6.1 to 27.4 centimeters) were reversed and K^ 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 (39.6 

 to 48.8 centimeters). As the foreshore eroded landward at a rate of 

 0.015 foot (0.46 centimeter) per hour and the outer offshore slope 

 steepened and prograded seaward with deposition at the higher elevations, 

 the shelf on the inner offshore grew in length in both directions and a 

 bar and trough developed. During this period of greatest profile develop- 

 ment, K^> rose sharply, reaching a maximum at 25 hours. As a result of 

 the high reflection, a significantly large standing wave developed, with 

 antinodes at the foreshore and station 18, over the steepest part of the 

 profile just seaward of the flat shelf. Between the first two antinodes 

 of the standing wave, over the flat shelf of the inner offshore, a clock- 

 wise circulation pattern developed, apparently driven by the counterclock- 

 wise circulation in the foreshore zone. Apparently, the circulation over 

 the inner offshore moved the sand to the edge of the shelf, but the lack 

 of current movement through the antinode prevented further transport and 

 thus increased the steepness. 



Between 25 and 70 hours, while the profile changed 3 feet (0.9 meter) 

 in the length of the shelf between the two reflecting zones (foreshore 

 zone and submerged offshore slope), K„ did not increase or decrease 

 significantly, but fluctuated over a range of 0.05. Part of this varia- 

 tion, which was greater than the 0.02 maximum variation in the fixed-bed 

 tank, may have been caused by the 90° change in phase difference between 

 the waves reflected from the two slopes as they separated. 



After 70 hours the seaward edge of the shelf began eroding, moving 

 landward, even though the foreshore was still retreating and the off- 

 shore was still prograding. Simultaneously, the clockwise circulation 

 pattern over the inner offshore began disintegrating and K^ began 

 decreasing. By 100 hours the bar had eroded and the trough had almost 

 filled completely. From 15 to 100 hours the outer offshore steepened, 

 with deposition at the upper elevations and erosion at -2.0- and 

 -2.1-foot elevations. The eroded material was moved seaward to form 

 a bar over part of the concrete bottom. 



40 



