to provide storm erosion protection beyond that already supplied by the break- 

 waters. Periodic tombolo formation, such as that exhibited by the Presque 

 Isle project, may temporarily store sediment, which is then released to the 

 downdrift during a storm. Salients have advantages over tombolos on coasts 

 that are subject to seasonal changes in wave direction. With a salient, 

 sediment does not have to be transported seaward of the breakwater to restore 

 longshore transport. When the transport is reversed, the salient undergoes 

 less drastic changes and the neighboring shores experience less seasonal ero- 

 sion or accretion. Tombolos function as T groins. Longshore sediment trans- 

 port is blocked and offshore losses are promoted. Mass transport from break- 

 ing waves can create a hydraulic head in the pocket between two adjacent 

 tombolos. Water piled up between the tombolos may then return through the 

 breakwater gap as a localized rip current, which can carry sediment offshore. 

 This process has been observed at Colonial Beach. With salients the hydraulic 

 head drives currents which can be dissipated alongshore as well as offshore. 

 Segmented detached breakwaters do not provide uniform erosion protection along 

 the entire project. This is especially true when one or a series of tombolos 

 develops. Legal problems could occur if the region involved is owned by 

 several different parties and storm damage is inflicted with partiality. 

 Accordingly, the engineer is often required to design a project that will 

 advance the shoreline in as spatially uniform a manner as possible. 



39. A tombolo allows access to the breakwater structure; however, this 

 has both advantages and disadvantages. Monitoring of the structure and main- 

 tenance or repairs are facilitated. However, beach users may be inclined to 

 climb on the structure or swim immediately adjacent to it, which can be dan- 

 gerous. One often overlooked advantage to a detached breakwater salient is 

 that there is quiet water immediately behind the structure available for 

 recreational use. (This sheltered water is ideal for very young beach users 

 or those who otherwise do not like to challenge waves.) The protection of the 

 breakwaters caused the beaches at both Presque Isle and Lakeview Park to 

 evolve into very popular family-use beaches not long after construction. 



Techniques for Controlling Shoreline Response 



40. After deciding how much beach area is needed, choosing the 

 preferred general planform of the shoreline, and if tombolos or salients are 



36 



