FUNCTIONAL DESIGN OF BREAKWATERS FOR SHORE PROTECTION: 

 EMPIRICAL METHODS 



PART I: INTRODUCTION 



1. The increase in public use of coastal areas during the 20th century 

 and a gradual relative sea level rise in many areas of the world have made 

 beach stabilization a priority for those who use coastal regions. An ideal 

 form of shore protection is one that would allow long-term stabilization of an 

 area in a cost-effective manner, protect upland structures to some degree 

 during storms, and provide an aesthetic recreational area, while avoiding 

 undesirable adjacent beach effects. All forms of shore protection (i.e., 

 groins, breakwaters, seawalls, revetments, bulkheads, beach- fill, etc.) have 

 certain disadvantages; however, the shore-parallel breakwater, placed at the 

 shoreline or offshore and designed either to intercept a portion of longshore- 

 moving sediment or to protect a placed beach- fill, has the potential to 

 perform close to the ideal for many types of coastal environments. 



2. Breakwaters provide protection to a length of shoreline by dissipat- 

 ing, reflecting, and diffracting incoming wave energy. Pope (1989) and Dally 

 and Pope (1986) discuss the terms that have evolved to describe the different 

 functional behaviors of the shore-parallel structure. Headland breakwaters 

 are constructed at or very near the original shoreline, designed to promote 

 beach growth out to the structure (tombolo formation) during all or part of 

 the water-level cycle. These structures tend to function as a transmissible 

 groin, intercepting all or a portion of the longshore -moving material. Pocket 

 beach breakwaters are a class of headland breakwaters, used to provide 

 protection to a placed beach- fill that is usually retained in the longshore 

 direction by terminal groins. The protected shoreline may extend partially 

 out towards the structure (termed a salient) , or a tombolo may form. Detached 

 breakwaters are constructed at a significant distance offshore of the original 

 shoreline and interact with incoming wave energy to produce a quiescent region 

 landward of the structure. Depending on structural and site parameters 

 (structure length, distance offshore, transmissibility , wave climate, etc.), 

 morphological beach response may be either a salient or tombolo. Reef 

 breakwaters are a type of detached breakwaters constructed with a low crest 



