Decreased Sediment Supply 



158. The impact of decreased sediment supply available to the profile can be examined by comparing 

 tests TOl and T03. As previously mentioned, tests TOl and T02 were conducted with approximately 

 10-percent less sediment in the berm than the equivalent prototype conditions. Therefore, test TOl 

 represents the case where there was less sediment available for redistribution across the equilibrium profile. 



159. Figure 24 shows representative comparisons between tests TOl and T03, while the complete set of 

 comparison plots is given in Figure E13 in Appendix E. The solid line is the test with 10-percent less 

 sediment, and the dashed line is the base test T03. There was not much difference between the two tests 

 other than the reduced sediment profiles appear to be slightly lower because less sediment was available for 

 depositing over the profile. 



160. If the offshore bar indeed has a sediment demand under given wave conditions, then it would be 

 expected that the comparisons would show the same offshore bar configuration with the nearshore profile 

 being scoured more deeply for the reduced sediment case. The comparisons shown in Figure 24 are 

 inconclusive in this respect because the observed variation in the offshore profile was not significant enough 

 to disprove this hypothesis. Other tests where sediment was withheld from the profile by placement of a 

 vertical seawall are discussed in Part VII of this report. 



Absorbing Wave Board 



161. Waves reflected from the beach and sloping revetment in the movable-bed experiments 

 necessitated stopping the wave machine after about 80 waves so that re-reflected waves from the wave 

 board did not adversely affect the experiment. This was the same procedure followed in the German GWK 

 prototype tests. Test T05 was conducted with a wave-absorbing capability activated on the wave board in 

 the 6-ft wave tank. This was the first time this feature had been used in laboratory tests since installation. 



162. The absorbing board has three wave gages spaced across on the face of the board that sense and 

 average the water level. This averaged value is compared with the specified value of water level that should 

 be present without any reflected wave energy, and any diff'erence is compensated by the appropriate 

 increase or decrease of board stroke. Present equipment limitations require that a lower frequency cutofl^ be 

 employed to avoid damage to the hydraulic components. This means that reflected waves with frequencies 

 below the cutoff frequency cannot be absorbed. 



163. Figure 25 compares test T06 (solid line), where waves ran continuously between profiling stops, 

 with base test T03, where stops occurred after 80 waves to allow the reflections to settle. As evidenced by 



