211. Barnett (1987) conducted 2-D laboratory tests using a movable-bed model scaled according to the 

 criteria given by Equation 6. Tests were conducted using regular waves and sand with a median grain size 

 of 0.15 mm. Profile measurements were made at 1/3 spacings across the wave tank and then averaged to 

 compensate for the observed cross-tank variations. Erosive test cases without a seawall were compared 

 with similar tests with a seawall located at different positions on the profile. Volumetric comparisons of the 

 "final" profiles indicated that the eroded volume in front of the seawall was less than the corresponding 

 erosion on the natural profile in 10 of the 11 comparisons. On average (as determined by linear regression), 

 61-percent less volumetric erosion occurred on the seawalled profiles. (Also see Barnett and Wang 1988). 



Impact of Seawall 



212. The approximate principle that the amount of sediment denied the profile by the presence of a 

 seawall is balanced by additional erosion in front of the seawall was tested in cases TIO and Til. The 

 primary difference between these tests and previous tests conducted in the flume was the presence in the 

 flume of a vertical seawall constructed of marine plywood. The seawall was positioned on the sloping 

 revetment approximately at the intersection of the still- water line and revetment. The seawall was 

 constructed such that it effectively prevented sediment behind it from eroding as the revetment became 

 exposed due to wave action. The presence of the sloping concrete revetment and subsequent wave-induced 

 exposure of the revetment make these tests somewhat unique in comparison with previous laboratory 

 studies that examined seawall impacts. 



Regular Wave Comparisons 



213. Profile development under regular wave conditions with and without the vertical seawall is 

 compared in Figure 30 for three diff'erent stages of development. The complete set of comparisons is given 

 in Figure E19 in Appendix E, and associated experiment documentation is presented in the appropriate 

 appendices. In Figure 30, the solid-hne profiles (test TIO) represent the profile development with the 

 vertical seawall in position, and the dashed-line profiles are from test T03 (no vertical seawall). After 



80 waves, profile development between the two tests is quite similar because the vertical seawall had just 

 become exposed during the last few waves, and its effect was negligible to this point. Note that the sloping 

 revetment is still covered with sand at the 80-waves profile. Even after 370 waves had impacted the initial 

 plane-sloping beach, little diff"erence between the tests in the profile development seaward of the vertical 

 seawall was observed. Gradually, however, differences between the two tests began to appear after 



85 



