of the presence and operation of the device was net erosion of 4 cubic feet 

 from the landward side of the device, and a net accretion of 22 cubic feet 

 on the seaward side. This net transfer of sediment seaward is probably an 

 indication of the effect of the steeper slope a short distance landward of 

 where the device was operating. That sediment which was flushed landward 

 probably slid down the slope into the trench and thence was transported to 

 the seaward side. 



d. Run 4. For this run, the device was moved about 17 feet far- 

 ther inshore than it had been for Run 3 (see Figure 9). The wave period 

 remained at 5 seconds, and the offshore water depth at 30 feet, but the 

 offshore average wave height was increased slightly to 1.6 feet. In order 

 to accommodate the lesser water depth, the rod connecting the flap valve 

 rack to the vertical supports was passed through the second flap valve from 

 the top, thus placing the uppermost flap valve almost totally above the 

 waterline of the device, and completely removing it from effective dredging 

 operation. With this configuration of three operative valves, the lower 

 edge of the bottom flap valve extended to a depth of about 14 feet beneath 

 the Stillwater surface. 



Like the preceding three runs. Run 4 was a static test, and of the 

 same 50-minute duration. The dredge setting and/or location had a profound 

 effect on the wave height as the average offshore impinging wave height was 

 1.6 feet, while the average wave height measured at a gage inshore from the 

 device was only 0.7 feet, a reduction of 56 percent. After Run 4, the entire 

 profile was surveyed to see what changes had occurred over its length during 

 the preceding portion of the test series. This survey showed that a rather 

 small amount of headward erosion of the shore had occurred above the still- 

 water line, in addition to the movement and slight enlargement of some of 

 the small nearshore bars (see Figure 9). In the vicinity of the device. 

 Run 4 produced the usual trench and increased the steepness of the slope 

 immediately landward of the device. The depth of the trench was less than 

 in previous runs; the width was about the same. Some accretion also took 

 place on the rim of the steep slope landward of the device. Offshore, there 

 was a small amount of filling in the trench left by Run 3, but some erosion 

 of the seaward rim. Still farther seaward, a small amount of accretion took 

 place. In that portion of the profile landward of the device, about 123 

 cubic feet of material accreted, while some 189 cubic feet eroded. Seaward 

 of the device, the profile was surveyed some 83 feet. Downslope from the 

 trench, 62 cubic feet had eroded, while 27 cubic feet had accreted. The 

 presence and operation of the device during this run produced a net erosion 

 of 56 cubic feet on its landward side and a net erosion of 35 cubic feet on 

 its seaward side. Presumably, accretion occurred seaward, outside the 

 surveyed area. 



e. Run 5 . Run 5 comprised the first mobile run of the test series, 

 that is, the device was moved a specified distance landward periodically 

 without any cessation of wave action (see Figure 10). The pre-run profile 

 was that which existed at the end of Run 4. The initial location of the 

 device was inshore of that of the preceding run by only about 4 feet, so 

 that it remained at the same setting with three valves operating. 



17 



