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configuration such as beach nourishment data. During the planning and 

 design stages of a project, beach profile data and aerial photography should be 

 acquired to provide an improved understanding of the nearshore system. 



Sediment budget 



A sediment budget is a quantitative balance of the sources (gains) and sinks 

 (losses) within a project area (Shore Protection Manual 1984; EM 1110-2- 

 1502). Sources of sediment include longshore transport, cross-shore 

 transport, aeolian or wind-blown transport, bluff recession, stream or river 

 sediments, and beach fill material. Losses of material to the system may 

 include longshore transport, offshore transport, aeolian transport, offshore 

 canyons, trapping by tidal inlets, blocking by structures, and dredging 

 operations. Generally, a sediment budget is developed for pre-project 

 conditions and then the effects of project construction can be evaluated by 

 making various assumptions regarding the project's effects on transport 

 (EM 1110-2-1617). 



Geotechnical data 



The physical properties of underlying soils should be investigated and 

 characterized by the collection of soil borings. In the coastal zone, beach 

 sands are often underlain by organic, compressible soils that may consolidate 

 under the structure's load and cause unwanted settlement. Additional 

 information on geotechnical data and design can be found in EM 1110-2-1903, 

 EM 1110-2-2906, and Eckert and Callender (1987). 



Existing structures 



An inventory of existing structures in the project vicinity and data on their 

 design and functional performance will assist in the design of a detached 

 breakwater system. Depending on their proximity and influence on the study 

 area, these structures may need to be incorporated into the design of the new 

 project. 



Review of Functional Design Procedures 



Design process 



Because of limited prototype experience, detached breakwater design in the 

 United States relies on a significant amount of engineering judgement, data 

 from a few existing breakwater projects for comparison, and an understanding 

 of basic coastal processes. The design process is an iterative one. An initial 

 breakwater configuration is assumed based on past experience at existing 

 breakwater sites and taking into account the site-specific concerns and 



Chapter 2 Functional Design Guidance 



