correction given in the SPM overestimates the amount of water carried over the 

 wall by wind. 



Methods to Reduce Wave Overtopping 



Recurved walls 



21. One method to reduce wave overtopping is to use a recurved wall 

 instead of a vertical wall. The Roughans Point seawall is vertical with a 

 small recurve at the crest. Observations indicate that the recurve is effec- 

 tive when the waves are small enough and the water depth at the wall great 

 enough to allow a reasonably coherent standing wave system to be established. 

 This system causes a vertical flow regime at the wall which is thrown seaward 

 by the recurve (Figure 12). The recurve is not effective when the crest 



V 





Figure 12. Wave overtopping the seawall at 

 Roughans Point, Massachusetts 



height of the incident wave approaches the elevation of the crest of the sea- 

 wall because the large, partial clapotis which forms for a moment in front of 

 the wall then spills over in large volumes of "green" water literally inun- 

 dating the seawall for a short time. 



22. For the inundation mode it is difficult to envision how any surface 

 feature of the wall could be very effective in reducing the overtopping rate. 

 For tests conducted in the Roughans Point study, the inundation mode of over- 

 topping occurred frequently when F' was less than 0.3. Thus, comparisons of 



21 



