on the backside of a low-crested breakwater. Unfortunately, the data scatter 

 shown in the figure undermines confidence in the suggested armor weights. 



4. In Australia, the breakwater at Rosslyn Bay was damaged severely 

 during Cyclone David in 1976 (Bremner et al. 1980). The crest height of the 

 structure was reduced as much as 4 m but still functioned effectively as a 

 submerged breakwater for over 2 years until it was repaired. Based on the 

 surprisingly good performance of the damaged Rosslyn Bay breakwater and the 

 findings from model tests, a low-crested design was chosen for the breakwater 

 at Townsville Harbor, Australia. This breakwater is unusual because it was 

 built entirely of stone in the 3- to 5-ton* range (Bremner et al. 1980). Reef 

 breakwaters, as described in this paper, are very similar to the Townsville 

 breakwater except a wider gradation of stone was used in the model breakwater 

 tests discussed herein. 



5. Seelig (1979) conducted an extensive series of model tests to deter- 

 mine wave transmission and reflection characteristics of low-crested break- 

 waters, including submerged structures. From these tests Seelig concluded 

 that the component of transmission resulting from wave overtopping was very 

 strongly dependent on the relative freeboard (i.e., freeboard divided by inci- 

 dent significant wave height). Recent work by Allsop (1983) with multi- 

 layered, low-crested breakwaters shows that wave transmission is strongly 

 dependent on a dimensionless freeboard parameter which includes the zero- 

 crossing period of irregular wave conditions. Allsop did not find substantial 

 wave period dependency in his evaluation of breakwater stability. He indi- 

 cates, however, that since wave transmission (which largely results from over- 

 topping) is dependent on period, then possible stability of the backside slope 

 would also be a function of wave period. 



Scope 



6. A study currently being conducted at the US Army Engineer Waterways 

 Experiment Station's Coastal Engineering Research Center is intended to docu- 

 ment the performance of low-crested breakwaters. This paper discusses labora- 

 tory model tests of reef breakwaters and provides information on their stabil- 

 ity to wave attack, wave transmission and reflection characteristics, and wave 

 energy dissipation. 



* Metric ton. 



