of the model study, the available statistical data describing the wave 

 environment, and other factors that influence the severity of wave attack. 

 The need for a model study, the type of structure required for optimum 

 performance, and the purpose and scope of the model study are usually 

 determined at the time preliminary designs are made, based on theoreti- 

 cal and experimental information available in the literature and field 

 data already available or obtained especially for the particular investi- 

 gation. If, during preliminary design, it is not possible to decide 

 which type of structure will best serve the purpose for which the struc- 

 ture is to be constructed, the purpose and scope of the model study could 

 be enlarged to include tests to determine comparable designs of two or 

 more types of structures so that the most economical structure could be 

 selected. A typical testing program will include tests of the structures 

 as originally envisioned by the design engineer, and tests of any modifi- 

 cations in design developed during the course of the investigation. 



Test conditions for model studies must be selected based on consid- 

 erations of all the variables that affect the structure's ability to per- 

 form an intended function at a minimum cost and with a minimum risk factor. 

 For the types of structures under consideration, the important variables 

 generally include (a) the shape and size of the structure, (b) the mate- 

 rials used in construction, (c) the shape, size, and density of the armor 

 units (if a rubble-mound structure), (d) the Stillwater depth at the sea- 

 ward toe of the structure, (e) the bottom slope seaward from the struc- 

 ture toe, (f) the range of astronomical tide, and (g) the largest wind 

 setup or storm surge (or setdown) expected to occur with sufficient fre- 

 quency that it should be added to the high tide (and subtracted from the 

 low tide) conditions selected for the testing program. For floating 

 breakwaters the testing program will usually include tests with differ- 

 ent types of mooring conditions. In the case of floating, pneumatic, 

 and hydraulic breakwaters (which are usually ineffective for conditions 

 other than deepwater and short -period waves), the tidal range, magnitude 

 of wind setup or storm surge, and the bottom slope seaward of the struc- 

 ture are not important variables for the proper functioning of the struc- 

 ture or the selection of test conditions. In the selection of test waves 

 for rubble-mound, vertical -wall, composite, and seawall types of coastal 

 structures, the possibility that the design engineer might recommend a 

 structure that would not be completely stable for the maximum storm wave 

 condition should be considered. This could occur if it is judged less 

 expensive to repair the structure after the occurrence of severe storms 

 than to select a design wave to keep the structure from being damaged 

 during its economic life. 



The largest and most destructive wave that can attack a rubble-mound 

 or vertical-wall structure is a function of the wave dimensions in deep 

 water, the bottom contours between deep water and the structure site, 

 water depth at the structure toe, bottom slope seaward of the structure 

 toe, and the seaside slope, crest height, and porosity of the structure. 

 Experiments to determine the limiting heights of both breaking and non- 

 breaking waves that can attack typical rubble-mound breakwater sections 

 have been conducted by Jackson (1968) and Weggel (1973). Similar tests 



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