necessary for construction. Other types of breakwaters include headland 

 breakwaters or artificial headlands, which are constructed at or very near to 

 the original shoreline. A headland breakwater is designed to promote beach 

 growth out to the structure, forming a tombolo or periodic tombolo, and tends 

 to function as a transmissible groin (Engineer Manual (EM) 1110-2-1617, 

 Pope 1989). Another type of shore-parallel offshore structure is called a 

 submerged sill or perched beach. A submerged or semi-submerged sill 

 reduces the rate of offshore sand movement from a stretch of beach by acting 

 as a barrier to shore-normal transport. The effect of submerged sills on 

 waves is relatively small due to their low crest elevation (EM 1110-2-1617). 

 Other types of shore-parallel structures include numerous patented commercial 

 systems, which have had varying degrees of efficiencies and success rates. 

 This technical report will focus on detached breakwater design guidance for 

 shoreline stabilization purposes and provide a general discussion of recently 

 constructed headland and low-crested breakwater projects. Additional infor- 

 mation and references on other breakwater classifications can be found 

 in Lesnik (1979), Bishop (1982), Fulford (1985), Pope (1989), and 

 EM 1110-2-1617. 



Prototype Experience 



Prototype experience with detached breakwaters as shore protection struc- 

 tures in the United States has been limited. Twenty-one detached breakwater 

 projects, 225 segments, exist along the continental U.S. and Hawaiian coasts, 

 including 76 segments recently constructed near Peveto and Holly Beach, 

 Louisiana, and another 55 segments completed in 1992 at Presque Isle, 

 Pennsylvania (Figure 2). Comparatively, at least 4,000 detached breakwater 

 segments exist along Japan's 9,400-km coastline (Rosati and Truitt 1990). 

 Breakwaters have been used extensively for shore protection in Japan and 

 Israel (Toyoshima 1976, 1982; Goldsmith 1990), in low to moderate wave 

 energy environments with sediment ranging from fine sand to pebbles. Other 

 countries with significant experience in breakwater design and use include 

 Spain, Denmark, and Singapore (Rosati 1990). Figures 3 to 5 show various 

 examples of international breakwater projects. 



United States experience with segmented detached breakwater projects has 

 been generally limited to littoral sediment-poor shorelines characterized by a 

 local fetch-dominated wave climate (Pope and Dean 1986). Most projects are 

 located on the Great Lakes, Chesapeake Bay, or Gulf of Mexico shorelines. 

 These projects are typically subjected to short-period, steep waves, which tend 

 to approach the shoreline with limited refraction, and generally break at steep 

 angles to the shoreline. The projects also tend to be in areas that are prone to 

 storm surges and erratic water level fluctuations, particularly in the Great 

 Lakes regions. 



In recent years, low-crested breakwaters of varied types have been used in 

 conjunction with marsh grass plantings in an attempt to create and/or stabilize 



Chapter 1 Introduction 



