4 Structural Design Guidance 



Structural Design Objectives 



Traditional high-crested breakwaters with a multi-layered cross section are 

 typically used for navigation purposes at entrance channels and harbors; but 

 may not be appropriate for a structure used to protect and stabilize a beach, 

 shoreline, or wetland. Adequate protection may be more economically 

 provided by a low-crested or submerged structure composed of a 

 homogeneous pile of stone. The greater tolerance of wave transmission at 

 such sites has resulted in low-crested rubble-mound breakwaters being widely 

 used or considered for use in beach stabilization, shore protection, and 

 wetland development or protection. Recent laboratory tests specifically related 

 to low-crested structures have resulted in empirical relationships to determine 

 both the stability and performance characteristics of low-crested rubble-mound 

 structures. The focus of this chapter of the report is aimed at the structural 

 aspects of rubble-mound breakwaters. 



The main structural design objectives of detached breakwaters are to ensure 

 that the structure remains stable and provides acceptable performance 

 characteristics throughout the project design life. Low-crested breakwater 

 design consists of determining the required crest elevation, crest width, 

 structure slope, and armor requirements to provide the desired stability and 

 functional performance under the anticipated design wave and water level 

 conditions. Structural guidance is provided to aid in the development of a 

 breakwater cross section to meet both the functional and structural needs of a 

 given project location. 



Design Wave and Water Level Selection 



In the selection of design water levels and design waves for a project, the 

 conditions critical to structure stability and performance must be considered. 

 The conditions represent critical threshold combinations of tide level, surge 

 level, wave conditions, etc., which, if surpassed, will endanger the project 

 and/or make the structure nonfunctional during their occurrence 



Chapter 4 Structural Design Guidance 



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