in both model and prototype terms, and the number of flap valves operating. 

 The depth of the deepest part of the device is the distance from the water- 

 line on the device, down to the lower edge of the lowest flap yalve. The 

 number of flap valves operating during a run was equal to the number of 

 valves extending below the axial supporting rod through the uppermost act- 

 ing valve, the vertical valve supports, and the horizontal flotation pad 

 support beams. The inactive valves were attached to the vertical valve 

 supports as were the active valves, but were suspended above the flotation 

 pads and thus out of reach of impinging waves. 



Table 6 lists the effect of the presence and operation of the device 

 on its landward side. Table 7 lists, similarly, the effect on its seaward 

 side. In the case of a static run, the landward side of the device was de- 

 fined as that portion of the pre- and post-run profiles extending from the 

 station over which the device was located, proceeding toward the inter- 

 section of the bottom profiles with the stlllwater line as far as the device 

 was believed to have caused changes. The seaward side, also in the case of 

 a static run, was similarly defined, but in the opposite direction. tn the 

 case of a mobile run, both the seaward and landward effects were defined 

 beginning Immediately under the final rather than the initial position of 

 the device. These tables list the computed volume of sediment in both 

 model and prototype terms, either accreted, that Is, where the post-run 

 profile had a higher elevation above the bottom than the pre-run profile, 

 or eroded, where the post-run profile had a lower elevation that the pre- 

 run' prof i le. These volumes were derived, in model terms, by p I an [metering 

 the two-dimensional area of the comparable profiles, and multiplying this 

 value by the width of the flume. The prototype volume was then obtained 

 by multiplying the model volume by the cube of the scale factor, 15^, or 

 3375, with both model and prototype values given in cubic feet. 



Table 8 lists the net effect of the presence and operation of the 

 device in two columns headed "Landward" and "Seaward", in both model and 

 prototype terms. These two columns show results of the summation of Tables 

 6 and 7, respectively. For example, Table 6 lists the amount of accretion 

 of sediment on the landward side of the device after Run I as 0.007 cubic 

 feet in model terms. Also, the amount of eroded sediment on the landward 

 side is listed as 0.003 cubic feet. Therefore, by subtraction, the net 

 resultant is accretion of 0.004 cubic feet on the landward side. Like pro- 

 cedures were followed to obtain the remainder of Table 8. The real sig- 

 nificance of this table is, however, somewhat uncertain. As has already 

 been stated, the profile surveys made after each run covered only that 

 portion of the bottom that was suspected of having been affected by the 

 presence and operation of the device. The distance covered, therefore, 

 was extremely variable; for example, after Run I, a distance. of 2 (.model) 

 feet was covered on. the landward side, with 3 feet being included in the 

 post-run profile on the seaward side. In contrast, however, a very notice- 

 able bar was formed inshore of the device during Run 7, so the surveyed 

 profile was expanded to cover 2.6 model feet landward and 5.5 feet seaward 

 of its final position. 



13 



