Indiana, on Lake Michigan. Burns Harbor frequently experiences greater than 

 desirable wave action in the harbor. Transmission by overtopping has in- 

 creased because of high lake levels in 1985 and 1986, and transmission through 

 the structure appears to be high due to the large size of the stone used in 

 the armor. Unless special placement of the armor is used, large armor stone 

 leave large void spaces, allowing greater wave transmission through the break- 

 water. Ahrens (1987) provides a quantitative relation for this occurrence. 

 Figure 7 shows wave transmission caused by a storm at Burns Harbor and pre- 

 dicted wave transmission using the reef breakwater transmission model. Fig- 

 ure 8 shows wave action at the Burns Harbor breakwater generating transmitted 

 waves in the harbor. Predicted transmission using the model is greater than 

 the observed transmission since the reef transmission model was developed from 

 physical model tests of very permeable rubble mounds with no core. However, 

 the model follows the trend of the observed data quite well. 



13. A physical method developed within the US Army Engineer Division, 

 Pacific Ocean, to cope with crown stability and overtopping during heavy wave 

 overtopping of rubble mounds is a ribbed concrete cap. Concrete armor units 

 key into the ribs and improve the stability of the crest, and the presence of 

 the ribs adds resistance to wave overtopping flow thereby reducing transmis- 

 sion (Markle 1982 and Markle and Herrington 1983) . Figure 9 shows the con- 

 crete rib cap on the breakwater at Hilo, Hawaii. The reef transmission model 

 is not applicable to concrete cap breakwaters without further experimental 

 work. 



14. Figures 2 through 7 give a rough idea of the value of a rather sim- 

 ple wave transmission model which was developed from conceptual ideas and cal- 

 ibrated and refined through the use of physical model tests. The reef trans- 

 mission model makes it very easy to investigate the influence of a variety of 

 variables on the transmitted wave height. Further, the model could be used to 

 project how the deterioration of a rubble structure might affect wave trans- 

 mission or how various rehabilitation concepts would improve the transmission 

 characteristics of the structure. The reef transmission model was not in- 

 tended as a rehabilitation tool, and many of the examples shown were using the 

 model outside the range of calibration, i.e. outside the range of conditions 

 of the laboratory tests. However, the model provides logical trends in Fig- 

 ures 2 through 7, even outside the range of calibration, because of improved 

 understanding of the wave transmission process (Ahrens 1987) . In developing a 



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