CHARACTERISTICS OF REEF BREAKWATERS 



PART I: INTRODUCTION 



1 . A reef breakwater is a low-crested rubble-mound breakwater without 

 the traditional multilayer cross section. This type of breakwater is little 

 more than a homogeneous pile of stones with individual stone weights similar 

 to those ordinarily used in the armor and first underlayer of conventional 

 breakwaters. 



2. In recent years a number of low-crested breakwaters have been built 

 or considered for use at a variety of locations. Most of these structures are 

 intended to protect a beach or reduce the cost of beach maintenance. Other 

 applications include protecting water intakes for power plants and entrance 

 channels for small-boat harbors and providing an alternative to revetment for 

 stabilizing an eroding shoreline. In situations where only partial attenua- 

 tion of waves on the leeside of a structure is required, or possibly even 

 advantageous, a low-crested rubble-mound breakwater is a logical selection. 

 Since the cost of a rubble-mound breakwater increases rapidly with the height 

 of the crest, the economic advantage of a low-crested structure over a tradi- 

 tional breakwater that is infrequently overtopped is obvious. Because the 

 reef breakwater represents the ultimate in design simplicity, it .could be the 

 optimum structure for many situations. Unfortunately, the performance of low- 

 crested rubble-mound structures, particularly reef breakwaters, is not well 

 documented or understood. 



Background 



3. A number of papers have noted that armor on the landside slope of a 

 low-crested breakwater is more likely to be displayed by heavy overtopping 

 than armor on the seaward face (Lording and Scott 1971, Raichlen 1972, and 

 Lillevang 1977). Raichlen discusses the characteristics of overtopping over 

 the crest and the inherent complexity of the problem. Walker, Palmer, and 

 Dunham (1975) give a carefully reasoned discussion of the many factors influ- 

 encing stability of heavily overtopped rubble-mound breakwaters. They also 

 show a figure which suggests what armor weight is required for stability 



