device, continued even more deeply to seaward and accounted for tt^e erosion 

 of 35 cubic feet that took place on that side of the device. Seaward and 

 downslope from the trough, 49 cubic feet of sediment accreted in a rather 

 thick layer extending about 36 feet seaward of the downslope trough limit, 

 about 48 feet from the device. Run I lasted about 50 minutes so the sedi- 

 ment movement took place at a rather rapid rate. Waves having an average 

 height of 1.8 feet in 30 feet of water impinged on the device and were 

 reduced in height 22 percent to 1.4 feet by its presence and operation. The 

 resultant energy released was used primarily to operate the device and to 

 move sediment. 



The device, located in front of a window in the sidewall of the tank, 

 could be observed in operation. However, after the first few waves, the 

 water was filled with suspended sediment which severely limited visibility 

 and photography. The activity that took place very close to the window 

 could be seen and gave the impression that the sediment in suspension was 

 primarily present in two vortexes, one on either side of the device, with 

 the seaward one being considerably larger in extent. 



These vortexes rotated rapidly, but at different rates, directions, and 

 at different times, the main impetus being provided by the trough-generated 

 current that flowed in a seaward di recti en beneath the device. This current 

 caused the larger, seaward vortex to spin in a counterclockwise vertical 

 direction at a rapid rate when the trough was passing. This spin direction 

 seemed to continue at a decelerating rate for some time after the trough had 

 passed and the passage of the subsequent crest had begun, then accelerated 

 again with the oncoming trough. Most of the seaward deposition seemed to 

 take place as the vortex was slowing down, beginning farther seaward and 

 progressing toward the device. As the crest passed, some sediment was seen 

 to flow through the opened flap valves but, relative to the whole seaward 

 vortex, the amount seemed to be quite small. 



Similarly, a smaller vortex was observed on the landward side of the 

 device. This vortex seemed to spin rapidly in a clockwise direction when 

 the trough was passing, but reversed direction with the passage of the wave 

 crest and spun counterclockwise quite slowly until the subsequent trough 

 arrived. The sediment on the landward side of the device was deposited 

 during the short periods of time when the spin reversal was taking place, 

 which may account for the thinness and unevenness of the accreted layer. 

 The narrowness of the window in the tank wall prevented observation of the 

 full scope of the activity within the flume, and observation from above was 

 prohibited by the density of-the black suspended material. The net effect 

 of the presence and operation of the device was to produce an equal net 

 accretion of 14 cubic feet over the surveyed areas of both sides of the 

 device. Due to the limitations of the post-run survey, it is not known 

 where the accreted material came from, but a net accretion on the landward 

 side of the device was at least initial ly promising though of such sma I I 

 amount as to possibly be within the error of measurement. 



15 



