Park Dike, 1978 Profile 



Model construction 



52 



The park dike model was constructed identically to the model with the 

 1991 profile, except that tests with the 1978 bathymetry were conducted 

 in the 18-in. flume rather than the 3-ft flume. Crest elevation of the park 

 dike was +24.0 ft mlw. 



Test conditions and results 



Table 17 lists conditions used to test the park dike. The swl's selected 

 were the highest water levels predicted for the SPN and the highest swl 

 observed during the 1978 storm. Similarly, wave periods were maximum 

 wave periods for the SPN and the 1978 storm. Wave heights were se- 

 lected as maximum wave height of the SPN plus lower wave heights to 

 provide a range of overtopping values. See Table 4, Profile 2, for SPN 

 conditions, and Table 2 for conditions in the 1978 storm. 



The wave generator in the 18-in. flume was unable to produce the maxi- 

 mum wave conditions selected for testing. For test conditions where the 

 wave generator was unable to produce the desired wave spectrum, the H^^ 

 was incrementally decreased by 10 percent until conditions were within 

 the limits of the wave generator. Water depths and wave periods were not 

 changed. Table 17 lists wave heights that were used in the test series. 



Tests 21 through 33 in Table 17 were tested with the same geometry of 

 beach, seawall, and dike elevations. For the remaining tests (34 though 

 45), the swl was kept constant at +16.5 ft mlw and the same dike elevation 

 of +24.0 ft mlw was maintained. Four of the test conditions in Table 17 

 (two wave heights at each of the two wave periods) were selected for each 

 of the three remaining sets of tests. Tests 34 through 37 measured overtop- 

 ping rates with the beach elevation raised to +13.1 ft mlw, and Tests 38 

 through 41 further increased the beach elevation to +16.8 ft mlw. For 

 Tests 42 through 45, the beach was returned to the 1978 profile elevation 

 of +9.3 ft mlw and the seawall crest elevation was reduced to +18.5 ft 

 mlw (approximate elevation of Revere Boulevard in the vicinity of Pro- 

 file 2). Tests 42 through 45 were meant to simulate conditions if the sea- 

 wall were to fail. 



Testing the park dike with the 1978 bathymetry produced very large 

 overtopping quantities. At swl = +16.5 ft mlw and Tp = 15.9 sec, the 

 smallest wave heights tested {H^^ = 8.9 ft. Test 21) caused sheets of water 

 to completely overtop the structure, with some spray passing over the en- 

 tire park dike while still in the air. Vertical spray exceeded the height of 

 the flume, and a board was placed on top of the flume to retain the spray. 

 These extreme cases of overtopping occurred when groups of large waves 



Chapter 5 Revere Dike Study 



