+24.0 ft +21 .5 ft 



Park Dike 



Concrete Slope in Wave Flume 



All elevations in feet mlw 



Figure 14. Cross section of model park dike 



were conducted with beach elevations at the seawall of +14.4, +15.4, and 

 + 19.9 ft mlw to test the effects on overtopping rates of an eroded beach 

 profile. 



Test conditions and results 



Tests were conducted for a prototype wave with H^^ = 12.7 ft, the larg- 

 est wave height of the design storm. Prototype wave periods tested were 

 Tp = 15.9 sec and 13.0 sec, corresponding to the peak periods of the SPN 

 and 1978 storm, respectively. Water depth was +16.6 ft mlw, the greatest 

 depth of the design storm. The beach profile tested was the 1991 post- 

 storm profile with a maximum beach elevation of +20.5 ft mlw. With 

 these test conditions, there was no measurable overtopping with the low- 

 est crest elevation tested (+24.0 ft mlw); therefore, higher crest elevations 

 were not tested under design storm conditions. A series of tests under less 

 severe conditions had been planned, but were not conducted because of 

 the lack of overtopping under the most extreme conditions of the SPN. 

 Test conditions and measured overtopping rates are listed in Table 15. 



Tests 1 and 2 were conducted with a seawall crest elevation of +21.3 ft 

 mlw and peak wave periods of 15.9 and 13.0 sec, respectively. Tests 3 

 and 4 were conducted under the same wave conditions, but with the sea- 

 wall crest lowered to +20.9 ft mlw. Minor overtopping was observed in 

 all four tests, but the overtopping quantities were not sufficient to mea- 

 sure. Qualitatively, higher overtopping rates were observed with the 

 higher seawall crest elevation and higher wave period. 



The sheet metal beach in front of the seawall was removed for Tests 5 

 and 6 to determine effects of beach erosion on overtopping rates. With a 

 beach elevation of +15.4 ft mlw, overtopping rates increased considerably, 

 although the overtopping was still not measurable at the 13.0-sec peak 

 wave period. 



For Test 7, the swl was increased by 1 ft to +17.6 ft mlw to simulate 

 possible sea level rise during the life of the structure. The additional foot 



48 



Chapter 5 Revere Dike Study 



