scope of the model investigation), the design, construction, and opera- 

 tion of stability models of coastal structures exposed to wave action 

 require (a) detailed information on the geometry of the structure and 

 materials of which the structure will be composed, (b) information con- 

 cerning the bottom materials upon which the structure will be situated 

 (except for floating, pneumatic, and hydraulic breakwaters which require 

 no foundation) , (c) the bottom contours along the alinement of the struc- 

 ture and seaward of the structure to a water depth of nearly one-half the 

 maximum wavelength, and (d) statistical data to determine the frequency 

 of occurrence of waves with different heights and periods at the struc- 

 ture site. 



Although accurate wave data are required to ensure that stability 

 of a structure is obtained by a safe and efficient design, adequate wave 

 records at the site are seldom available. However, when wave records are 

 available, or if recorders are installed especially for a particular pro- 

 ject from which the needed statistics can be prepared, the methods of 

 analysis and presentation of the data as proposed by Draper (1966) are 

 suggested. In the absence of wave records near the site of a proposed 

 structure, the necessary statistical wave climate data can be determined 

 by the forecasting and hindcasting techniques for deepwater stations off- 

 shore of the structure site (see Bretschneider, 1966 and U.S. Army, Corps 

 of Engineers, Coastal Engineering Research Center, 1977). The deepwater 

 wave data must then be transferred to the site of the proposed structure, 

 which is usually located in shallow water relative to wavelength (except 

 for floating, pneumatic, and hydraulic breakwaters) , taking into consid- 

 eration the effects of refraction, diffraction, reflection, and bottom 

 friction phenomena. This can be done analytically either by graphical 

 or computer methods (Bretschneider and Reid, 1953; Johnson, 1953; Dobson, 

 1967; IVhalin, 1971; U.S. Army, Corps of Engineers, Coastal Engineering 

 Research Center, 1977). The results of these studies will provide wave 

 heights, wavelengths, and directions of approach at the site of the struc- 

 ture (or at the outer ocean limits of the model if a three-dimensional 

 model study is conducted) as a function of the corresponding deepwater 

 wave conditions. In most model studies concerned with the stability of 

 coastal structures, the wave statistics can be presented in the form of 

 frequency of occurrence data for the significant wave heights and wave 

 periods (Hwg, Twg). However, for some studies the effects on the 

 structure of irregular wave trains which more closely represent the 

 characteristics of actual prototype wind-generated waves must be de- 

 termined. Prototype wave-spectra data are necessary for tests of this 

 type. The maximum waves that can attack a coastal structure is depend- 

 ent on the wave steepness, H/A, relative depth, d/A, slope of the 

 bottom seaward of the structure, and the geometry and percent voids of 

 the structure (Miche, 1944b; Danel, 1952; Kishi, 1959; Jackson, 1968; 

 Weggel, 1973; U.S. Army, Corps of Engineers, Coastal Engineering Research 

 Center, 1977). 



Floating, pneumatic, and hydraulic breakwaters are generally impracti- 

 cal except for conditions where the water depths are large compared with 

 wavelength. Thus, detailed bottom contour data (used for wave refraction 



334 



