through the structure that the transmitted wave heights are slightly higher 

 for the reef breakwater with 8,000-lb stone than the reef with 5,000-lb stone. 

 This comparison illustrates that larger stones create larger void spaces which 

 allows slightly higher transmission through the structure (all other factors 

 being equal). When transmission is dominated by overtopping, the transmitted 

 wave heights are about the same. 



11. Figure 5 uses the reef transmission model with wave conditions and 

 stone size the same as those in Figure 2 but with a water depth reduced from 

 20 to 12 ft and the crest heights of the reefs reduced in proportion to the 

 water depths. Comparison of Figures 2 and 5 indicates that the wave trans- 

 mission is slightly greater for a reef in a 12-ft water depth than it is for a 

 reef in a 20-ft water depth because the cross-sectional area of the structure 

 has been reduced more in changing from a water depth of 20 to 12 ft than the 

 reduction in wave length. The cross-sectional area of the structure is im- 

 portant both for transmission through the reef and for transmission by over- 

 topping. A wider structure is more effective in reducing transmission than a 

 narrower reef breakwater with the same height. Since it might be easier to 

 rehabilitate a structure by increasing the width rather than by increasing the 

 height to achieve a desired level of transmission, this approach is explored 

 using the reef transmission model in Figure 6. Figure 6 has the same wave 

 conditions and stone size as used for Figure 2, but in Figure 6 only one crest 

 height of 24 ft is shown having three different cross-sectional areas. The 

 various cross-sectional areas were obtained by using crest widths of 3, 6, and 



12 stone diameters which give cross-sectional areas for the reef of 1,127, 



2 

 1,355, and 1,810 ft , respectively. In Figure 2 the reef with a crest height 



of 28 ft (the lowest transmission trend) has a cross-sectional area of 



2 

 1,482 ft . Comparison of Figures 2 and 6 shows that the reef with a height of 



2 

 28 ft and a cross-sectional area of 1,482 ft allows less wave transmission 



than the reef with a crest height of 24 ft and a cross-sectional area of 

 1,810 ft. The comparison suggests that it is more effective to reduce trans- 

 mission by repairing the reef's crest than increasing its width. Of course, 

 other factors would have to be considered such as the relative difficulty of 

 increasing the crest height versus increasing the cross-sectional area without 

 increasing the crest height. 



12. An example of the reef transmission model applied to an existing 

 structure is furnished by the wave transmission occurring at Burns Harbor, 



12 



