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are identified, and similarity is attained for the most dominant or severe 

 condition. In some cases the geometric scale is distorted because modeling 

 one dimension (i.e., horizontal length) may cause another dimension (i.e., 

 depth, sediment diameter) to be extremely small or large, which is impractical 

 or results in improper flow conditions. In general, physical hydraulic models 

 are classified as undistorted fixed-bed, distorted fixed-bed, or movable-bed, 

 which is usually distorted because the model and sediment scales are different. 



Fixed-bed models basically mean the bed, or bottom, is not moving. 

 Typically, the bed is constructed to the required depth contours using concrete 

 mortar. An undistorted fixed-bed model has the same geometric scale for all 

 length dimensions (i.e., length, width, depth, characteristic size, etc.), and 

 geometrically distorted models scale one of the dimensions or characteristic 

 size at a different geometric scale. For example, the width is scaled 1:100 

 and the depth is scaled 1:10. 



In coastal applications the bed is usually sediment, and it can move as a 

 result of the hydrodynamic forces exerted by the moving fluid medium. 

 These forces are caused by coastal currents, waves, and water level changes. 

 Complete three-dimensional movable bed models are the best approach to 

 model applications where knowledge of sediment movement is desired such as 

 is the case for determining the performance of a detached breakwater system. 

 However, these models do not assure total similitude and the cost, complexity, 

 and time required to conduct experiments result in modified movable bed 

 models, which do not satisfy all of the primary similarity requirements. 

 Therefore, a combination of fixed-bed modeling, tracer studies, and movable- 

 bed modeling has been employed at WES. 



The WES has numerous large and small physical model facilities for 

 conducting fixed- and movable-bed model tests and sediment tracer studies. 

 The US ACE guidance for physical modeling of coastal phenomena is 

 described by Hudson et al. (1979). Authorative references related to physical 

 modeling or model similitude such as Langhaar (1951), Keulegan (1966), 

 Yalin (1971), and Schuring (1977) are additional sources of guidance for the 

 conduct of physical modeling in the laboratory. Hughes (1993) addresses 

 fixed- and movable-bed modeling specifically for coastal engineering, with a 

 chapter that is completely devoted to movable-bed modeling and incorporates 

 the latest knowledge from the engineering and scientific communities. The 

 open literature is another source for guidance and examples of physical 

 modeling procedures and experiences. Frequently referenced studies of 

 Kamphuis (1975), Noda (1971), and Le Mehaute (1970) describe guidelines 

 and procedures for movable-bed modeling and tracer studies. 



Summary of procedures for physically modeling shoreline response to 

 detached breakwaters 



Over the past two decades, physical modeling procedures have been 

 developed and used by WES to evaluate detached segmented breakwaters. 



Chapter 3 Tools for Prediction of Morphologic Response 



