PART II: TECHNIQUES FOR DETACHED BREAKWATER DESIGN 

 Overview 



7. Techniques for designing detached breakwater systems can be classi- 

 fied into three categories: models, which numerically or physically simulate 

 coastal response to a proposed design; empirical methods, which relate 

 proposed project variables to beach response based on observed prototype and 

 model results; and prototype assessment, in which a version of the final 

 design is constructed, evaluated, and refined in the field. Each design 

 classification has inherent advantages and disadvantages. 



8. Numerical and physical models are powerful tools that can give 

 detailed information about coastal response to a particular design; however, a 

 detailed prototype data set is usually required for calibration, verification, 

 and simulation. The shoreline response model GENESIS (GENEralized Simulation 

 model for Shoreline Change) is designed to simulate beach response to a 

 variety of erosion control structures and was successfully used to simulate 

 shoreline change at the Lakeview Park breakwater project (Hanson and Kraus 

 1989). Physical model tests can be expensive and time-consuming, and numeri- 

 cal model simulations can mislead the designer through model instability or 

 accurate solutions to inaccurate input conditions. Empirical relationships 

 are quick, inexpensive methods for evaluating beach response to a proposed 

 design; however, often the relationships have oversimplified design variables 

 and expected prototype response. Empirical relationships rarely are able to 

 predict complicated structure -induced phenomena such as the formation of rip 

 currents in the vicinity of the project, or the extent of project influence on 

 adjacent beaches. Where feasible, a prototype assessment of a proposed design 

 is the best method for refinement of the final design. However, a prototype 

 evaluation may be prohibitively expensive, and the construction of a poor 

 design alternative may make it publicly and politically difficult for funding 

 of the final project. 



9. To ensure a successful project, the iterative use of various design 

 techniques is recommended. Dally and Pope (1986) suggest a three-phase design 

 process: first, a desk- top study employing various empirical relationships to 

 identify design alternatives; second, either a physical or numerical model 



