the figure, the absorbing wave board produced a significantly different response from the standard method 

 of stopping wave generation more frequently. The profiles formed by the absorbing wave board exhibit 

 smoother features and substantially more movement of sediment to the deeper portions of the profile. In 

 addition, berm erosion was more pronounced during the intermediate stages of profile development when 

 wave absorption was being performed. 



164. Examination of the wave records from the absorbing board test reveals that the system correctly 

 removed the reflected waves at the incident frequency, but the procedure produced a spurious long wave at 

 a frequency below the cutoff frequency. Thus, the incident waves attacked the profile while the short-term 

 mean water level was oscillating up and down. When the water level was elevated, more of the berm was 

 susceptible to erosion, and when the water level was depressed, the waves moved more sediment into 

 deeper water. During the test, it was observed that the break bar feature was migrating back and forth due 

 to the low-frequency oscillation in the flume. 



165. This first test of the absorbing wave board indicated that it will probably be necessary to use this 

 capability in conjunction with spurious long wave suppression techniques when attempting to generate 

 monochromatic waves with active absorption. 



Summary of Perturbation Tests 



166. Movable-bed physical model tests designed to examine the effects of parameters thought to be 

 important in reproducing prototype-scale behavior were conducted in the 6-ft wave tank. Increasing the 

 height of the regular waves promoted further offshore movement of sediment and a corresponding 

 adjustment of the surf zone profile. Similar behavior was observed when the wave period was decreased by 

 10 percent. This similarity is probably related to both perturbations resulting in similar increased values of 

 wave steepness. 



167. The importance of preserving the fall speed parameter was confirmed by comparing tests where 

 the hydrodynamics were varied from the Froude criterion in order to maintain equal values of H/wT 

 between experiments. Although good results were obtained in this instance, it is still recommended that 

 the Froude criterion be adhered to, as well as maintaining the same value of fall speed parameter. 



168. Grain size perturbation was examined using previous results of Schulz (1985). Qualitatively, the 

 behavior was consistent with the established scaling criteria, at least for the case of the undistorted scale 

 model. 



169. Differences in initial profile did not substantially affect the ultimate outcome at near-equilibrium; 

 however, short-term differences were expected and were observed. For reproducing prototype-scale events, 

 it was concluded that accurate reproduction of the offshore profile is desirable, whereas accurate details of 



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