to three feet. Run 9 was a static run in order to observe the single- 

 station behavior of the device under this new set of wave conditions. 

 The run was about one hour and 17 minutes In duration. As may be noted 

 in Figure 14, the device was located about one-third of the way down the 

 final offshore slope. This slope, prior to Run 9, continued down to the 

 tank bottom rather evenly with but a small level step about one-third of 

 the way up from the bottom. The lower edge of the deepest flap extended 

 to a depth of about 14 feet below the stillwater line. A trench of con- 

 siderable width and depth was dug during Run 9, and caused the accretion 

 of a rather sizable mound landward up the slope. Seaward of the trench, 

 the device caused the accretion of two smaller layers of sediment, one 

 immediately seaward of the trench rim, and the other immediately seaward 

 of the previously mentioned level step In the slope. These two areas of 

 accretion were separated by a small area of erosion when the level step 

 in the slope had been. 



Landward of the device location, about 132 cubic feet accreted, (all 

 in the mound) and 82 cubic feet eroded (all in the trench) for a net gain 

 of 50 cubic feet. Seaward of the device, an erosion of 149 cubic feet 

 occurred, mostly from the trench but with some from the downslope step, 

 while the two areas of accretion seaward amounted to about 154 cubic feet, 

 a net accretion of 5 cubic feet. The extra accretional material was most 

 probably contributed both from offshore and headward erosion not surveyed. 

 The results of this run Indicated that the device might be somewhat 

 effective in waves of longer period. 



j. Run 10 . The purpose of Run 10 was primarily to attempt to 

 move the mound of material accreted landward of the device during Run 9 

 farther Inshore. As may be rioted in Figure 15, this did not happen. Run 

 10 was of the mobile type, with the device being moved approximately every 

 hour and 17 minutes for a total distance of 5 feet with the device at two 

 locations and a total running time of 2 hours and 35 minutes. At its final 

 location, the flap valve rack was tilted 30° with the lowest flap nearer 

 the shore. This was done to attempt to force the sediment, placed in sus- 

 pension by the under-device current generated by the passage of the wave 

 trough, to remain closer to the seaward side and so make more suspended 

 sediment available to be flushed through the open valves with the passage 

 of the subsequent crest. As the device would be working in shallower water 

 than it was in Run 9^ It was set so that two valves would be operating. At 

 this setting, the lowest edge of the deepest flap would extend about 9.5 

 feet beneath the stillwater line with the device in a vertical attitude. 



For this run, the waves had the same 9-second period as in Run 9, but 

 their offshore height was decreased a small amount to average 2.7 feet in 

 30 feet of water. The device* caused a very small mound of accretion (see 

 Figure 15) rather high up on the level portion of the profile above the slope. 

 Seaward of this small mound, the device eroded a considerable amount of ma- 

 terial down the slope to the wide, but rather shallow, trench dug during Run 

 10. This erosion created a gentler seaward slope, but removed all of the 

 material accreted landward of the device during Run 9, plus more materia! 

 up the slope. Seaward of the device location during Run 10, a large mound 

 of accretion more than filled the large trench created during Run 9. 



21 



