the device had operated over a distance of about 30 feet. As in Run 13, 

 the device had a vertical attitude with 3 flaps operating, the lowest one 

 extended about 14 feet below the Stillwater line. The decrease in the 

 water depth lowered the maximum elevation of wave attack on the shoreline 

 and greatly decreased the amount of headward erosion that occurred during 

 this run. However, some erosion did take place, providing sediment which 

 created an offshore bar and a rather thick layer seaward down the shelf. 

 The device dug a deep, wide trench and deposited mounds of material near 

 both the inshore and offshore rims. 



Landward of the device, 499 cubic feet accreted, and 397 cubic feet 

 eroded; on the seaward side, 476 cubic feet eroded, and only 375 cubic feet 

 accreted. A net accretion of about 100 cubic feet resulted on the landward 

 side and a net erosion of the same amount resulted seaward. This run termi- 

 nated the testing under this particular set of wave conditions. 



o. Run 15 . The purpose of Runs 15 and 16 was to observe the 

 operation of the device in waves of low height and long period. Such wave 

 conditions naturally tend to cause the accretion of material on beaches. 

 Accordingly, the offshore water depth was set at 30 feet, the wave period 

 at 15 seconds, and the average offshore wave height at 2.8 feet. A 1:15 

 molded slope was subjected to these waves for approximately 154 hours until 

 a new equilibrium profile was obtained as shown in Figure 20. The device 

 was then set in the vertical position so that 3 flaps operated, the lowest 

 about 14 feet below the stillwater line. As a mobile run was required, the 

 device was moved 3 feet approximately every hour during a total test time 

 of about 5 hours and 49 minutes, a total distance of 15 feet. The rather 

 long wave used in attaining an equilibrium profile, created a broad, essen- 

 tially bimodal, offshore bar over which the device operated during Run 15. 

 The device was positioned between the peaks and, as usual, dug a trench 

 beneath it, the deepest portion thereof being near its final station. A 

 group of small mounds accreted on top of the inshore lobe of the bar, land- 

 ward of the trench rim. Similarly, a single mound accreted atop the more 

 offshore peak on the bar seaward of the trench. Farther offshore, this 

 accreted sediment tapered down the slope in a thin filet. 



Landward of the device, 49 cubic feet accreted, and only 35 cubic feet 

 eroded, leaving a net gain of 14 cubic feet. Seaward of the device, much 

 more activity was noted with the accretion of 124 cubic feet and the erosion 

 of 94 cubic feet. The amount of sediment accreted landward of the device was 

 considered too small to attempt to move it toward the shore, so the device 

 was moved inshore of the bar for the next run. 



p. Run 16 . The water depth remained at 30 feet for Run 16, the 

 offshore wave height at 2.8 feet, and the period at 15 seconds. As in Run 

 15, the device remained set with 3 operating flaps extending to 14 feet below 

 the Stillwater line. This mobile run lasted 19 hours and 22 minutes, with 

 the device being moved 3 feet about every hour, for a total distance of 57 

 feet. Several small low mounds accreted slightly above and below the still- 

 water shoreline (see Figure 21). The device eroded away the inner bar and 

 some of the slope, which probably supplied not only the small amount of 



24 



