during preceding runs. The mound which accreted during Run 5 on the land- 

 ward rim of the steep slope and some of the upper portion of that slope 

 eroded away. Most of the sediment derived from this erosion filled the 

 trench dug at the base of the slope at the final device position of Run 5. 

 During Run 6, the profile inshore of the''device had a gentle slope and sub- 

 sequently was more receptive and retentive of the sediment placed in sus- . 

 pension and deposited by the device. The largest mound of accreted material 

 was deposited just landward of the inshore rim of the device-dug trench, 

 with smaller assemblies of accreted sediment farther landward. In all, on 

 the landward side of the device withJn the distance covered by the survey, 

 62 cubic feet of material accreted and 46 cubic feet eroded, resulting in 

 a net inshore gain of 16 cubic feet. Seaward of the device location, how- 

 ever, 58 cubic feet of sediment eroded, while 25 cubic feet accreted in the 

 distance surveyed, giving a net loss of 33 cubic feet. 



The accretion of such a volume of material on the landward side of the 

 device tends to support the hypothesis that the device operates more effect- 

 ively on a gentle slope than on a steep slope. 



g. Run 7 . Run 7 served as a mobile test of the device in shallow 

 ■water, over a more moderate slope. As in Run 6, only one flap valve was 

 operable. The initial location was 9 feet inshore of the position during 

 Run 6, and it was operated in waves having a 5-second period, but only a 

 I. 1-foot average height in 30 feet of water. Due to the mound of accretion 

 that developed during the run, the inshore wave gage had to be moved to 

 various locations as noted on Figure 12. The average inshore wave height, 

 computed from the various gage measurements, was reduced by the presence 

 and operation of the device, about 46 percent to 0.6 feet. As a small 

 amount of sediment had been accreted on the landward side of the device 

 during Run 6, one of the main purposes of Run 7 was to attempt to move the 

 mound farther inshore, and, if possible, enlarge it in the process. For 

 the duration of this run, the device was moved shoreward 3 feet approxi- 

 mately every hour and 56 minutes, for a total running time of 25 hours and 

 10 minutes, and a total distance of 36 feet. 



The results of this run were most interesting. About 14 feet landward 

 of the final device location, beginning at the inshore rim of the device- 

 dug trench, was a large mound of accreted sediment which attained a maximum 

 elevation of 0.75 feet above the stillwater line. This mound of accreted 

 material terminated about 40 feet inshore from its point of origin. This 

 occurrence resulted in the creation of an offshore bar with a back bay 

 inshore of it. The beach area profile, however, changed almost negligibly. 

 The trench beneath the device was deeper and wider than any previously 

 noted. The trench created during Run 6 was filled for the most part by 

 the accretion of material placed during Run 7, but no other accretion 

 occurred within the surveyed area seaward of any of the device locations. 

 Landward of the final location, 218 cubic feet of material accreted and 

 only 35 cubic feet eroded; the net accretion of 183 cubic feet was in the ' 

 form of the inshore bar. Seaward of the final location, 38 cubic feet of 

 sediment had accreted and 319 cubic feet had eroded, a net erosion of 281 

 cubic feet. 



