Influence of a Seawall and Beach Fill 



524. The numerical model has the capability of simulating the influence 

 of a seawall on beach profile evolution. The shoreward boundary of the 

 calculation grid is located at the seawall preventing transport of material 

 across this cell. The seawall only affects changes in the beach profile if it 

 is exposed to incident waves. Overtopping is not simulated by the model, and 

 it is assumed that the height of the seawall exceeds the runup height (or 

 local wave height) . 



Profile with seawall 



525. A hypothetical example was modeled to evaluate the effect of a 

 seawall on beach profile evolution during storm conditions. The initial 

 profile and wave data from CE Case 400 (Figure 60a) were used, and a seawall 

 was placed on the foreshore, approximately at the still -water shoreline, 

 protecting the subaerial part of the profile from wave attack. The simulation 

 result is displayed in Figure 85, which shows the calculated beach profile at 

 selected time -steps with a seawall on the foreshore and the beach profile at 

 the last time-step without a seawall. The wave height distribution across 

 shore is shown at the last time-step for the seawall calculation. 



525. The evolution and size of the bar were similar in the simulation 

 with and without the seawall, the bar being somewhat larger and located more 

 seaward for the case without the wall. The main difference was the amount of 

 material eroded in front of the seawall and shoreward of the bar. With the 

 seawall present, the width of the surf zone was much shorter, requiring more 

 material to be moved before an equilibrium beach shape developed. The 

 subaerial eroded volume for the case without the seawall approximately agreed 

 with the extra volume eroded in front of the seawall. 



527. The approach to equilibriuim was more rapid for the seawall case, 

 indicated by the slightly more gentle inshore profile slope. The longer time 

 elapsed before equilibrium was obtained for the case without the seawall was 

 caused by the larger extent of the profile involved in redistribution of sand. 

 Since the depth in front of the seawall was greater than for the case without 

 the wall at the corresponding location, the height of the broken waves was 

 larger (compare with wave height distribution in Figure 60a). 



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