PART V: SUMMARY AND CONCLUSIONS 



27. A number of revetment configurations were tested for effectiveness 

 in reducing irregular wave overtopping of the Roughans Point seawall. Results 

 of the study are summarized in Figures 21 and 22. The tests indicate that a 

 standard riprap revetment in front of the wall with the top of the riprap 

 close to the top of the wall (Configuration 2, as recommended by NED) is not 

 the most effective configuration for reducing overtopping. Configuration 4, a 

 riprap revetment with a relatively wide berm at +8 ft NGVD and a wall crest 

 elevation of +17.6 ft NGVD proved to be the most effective overall revetment 

 configuration unless a cap is added to the seawall. This berm configuration 

 appeared to be high enough and wide enough to dissipate wave energy well but 

 still low enough so that the seawall provided an effective discontinuity to 

 the wave and runup flow and allowed the recurve to function efficiently. To 

 obtain the maximum effectiveness, the berm should have an elevation equal to 

 the average annual high water event, be as wide as possible, and intersect the 

 seawall low enough so that a major discontinuity to wave action and runup flow 

 is maintained. By higher expected water levels a recurrence interval in the 

 range of 1 to 5 years is implied. These findings appear to be consistent with 

 recent research conducted at H.R.S. Wallingford on irregular wave overtopping 

 of sea dikes (see Owen (1982) and Allsop*). 



28. Increasing the height of the seawall is also a very effective 

 method to reduce wave overtopping, although for many situations this option is 

 not acceptable. 



29. A new method to compute overtopping rates caused by irregular wave 

 conditions has been presented which seems to have several advantages over the 

 current method of computing irregular wave overtopping rates given in the SPM 

 (1984). The method's advantages are that it: 



a. Is simple. 



b. Does not use the runup or potential runup to compute overtopping 

 rates- 



c. Is naturally well adapted for use with irregular wave conditions. 



d. Provides a simple way to compare and rank the effectiveness of 

 various structural configurations in reducing wave overtopping. 



Personal communication with N. W. H. Allsop, Hydraulics Research Limited, 

 Wallingford, Oxfordshire, England, 1985. 



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