wave trains being used or by inaccuracies in the collection and measure- 

 ment. However, Tests 27 through 29 differed only in wave height, and 

 Test 27 with a wave height of 9.6 ft had a low overtopping rate relative to 

 Tests 28 and 29. Similarly, Tests 30 through 32 differed only in wave 

 height, and Test 30 with a wave height of 9.9 ft had a low overtopping rate 

 relative to Tests 31 and 32. In each of these sets of tests, wave heights 

 around 9 to 10 ft were seen to produce surprisingly low overtopping. This 

 trend of low overtopping rates was observed only with a beach elevation 

 of +9.3 ft mlw and was not observed in Tests 34 through 41, which used a 

 higher beach elevation, or in Tests 42 through 45, which used a lower sea- 

 wall elevation. 



As expected, reducing the swl to +14.8 ft mlw in Tests 28 through 32 

 greatly reduced overtopping rates, while increasing the swl to +17.6 ft in 

 Test 33 nearly inundated the structure. 



Raising the beach elevation in front of the seawall to +13.1 ft mlw in 

 Tests 34 through 37 decreased overtopping rates, and further increasing 

 the beach elevation to +16.8 ft in Tests 38 through 41 further decreased 

 overtopping rates. The only test of the park dike with the 1978 profile 

 that did not produce overtopping was Test 41 with the beach elevation at 

 + 16.8 ft mlw. 



Tests 42 through 45 returned the beach profile to the conditions of the 

 1978 survey (+9.3 ft mlw) and reduced the seawall elevation 2.8 ft to 

 + 18.5 ft mlw. Overtopping rates were less than under the same conditions 

 but with the seawall intact (Tests 21, 23, 24, and 26) for Tests 42 through 

 44, and showed little change in Test 45. This was consistent with the find- 

 ing reported above in the tests of the park dike with the 1991 profile; i.e., 

 higher overtopping rates were obtained with the higher seawall elevation. 



Rubble-Mound Dike, 1978 Profile 



Model construction 



The rubble-mound dike model was constructed in the same manner as 

 the 1991 profile, but a smaller armor stone was used. Although specific 

 tests for stability were not conducted, there was no movement of armor 

 stone observed on tests with the 1991 profile. The armor stone was there- 

 fore reduced to crushed gravel passing a 5/8-in. sieve and retained by a 

 1/2-in. sieve. The model armor stone had an average weight of 0.011 lb 

 per stone (336 lb prototype). 



54 



Chapter 5 Revere Dike Study 



