development sand may be transported seaward of the structure, possibly 

 restoring the longshore transport rate. However, this usually involves 

 deflecting sediment into deeper water where it may be lost to the littoral 

 system. Even if transport is restored, the downdrift beach usually erodes due 

 to the temporary deficiency of longshore-transported sand and the long-term 

 increase in offshore losses. In addition, tombolo development will tend to 

 promote offshore losses. The bulge in the shoreline resulting from oblique 

 wave attack can be expected to be asymmetric, with its shape depending on the 

 following: (a) structure length and distance offshore, (b) nearshore wave 

 conditions, and (c) sediment characteristics. Figures 4 and 5 are examples of 

 connected and nonconnected formations (i.e., tombolos and salients) that 

 developed in response to oblique wave angles. In general, tombolos are 

 pointed and have concave sides (Figure 4) , while salients are more rounded 

 (Figure 5) . 



11. Any structure that causes local accretion of sand may also cause 

 damage to downdrift beaches if it removes material from the longshore system. 

 Adding beach fill to the project site is a means of avoiding or minimizing 

 this effect. A sufficient amount of sand should be placed to equal the amount 

 which would otherwise be removed from the littoral system by the breakwater. 

 Designing a detached breakwater requires prediction of the resultant equilib- 

 rium beach and the additional amount of sand necessary to maintain that stable 

 shoreline. By artificially adding an equal amount of fill, there should, in 

 principle, be no net adverse impacts on the neighboring shores. This is a 

 general principle which should be rigorously examined for any proposed proj- 

 ect. Even with the initial placement of beach fill, short-term variations in 

 the wave climate at a site can result in unacceptable erosion on neighboring 

 shores. 



12. Accurate prediction of shoreline response to detached breakwaters 

 is beyond the present state of the art, but these predictions must be approxi- 

 mated as a fundamental requirement for structure design. To do this, the 

 designer needs to take advantage of many different tools to gain insight into 

 the interrelationship of project and processes. This should involve studying 

 existing breakwater projects and applying a basic understanding of coastal 

 processes. The next two parts present a review of relevant breakwater proj- 

 ects constructed in the United States and discuss the parameters to be con- 

 sidered in breakwater design. 



11 



