the structure. Some general trends of higher stability on heads and for 

 oblique wave attack can be seen, but the trends are not well defined. For 

 this reason, a lower limit line has been incorporated into Figure 14. When 

 designing for breaking waves and designs are not being verified and/or 

 optimized with physical model tests, values of N^ equal to or less than 

 those defined by this line should be used for design. In addition, design for 

 conditions outside the ranges of d 1 /d s and d s /L s tested in the model (as 

 shown in Figures 11 and 12) should be carefully examined. This lower limit 

 line also has been incorporated into a plot with Brebner's and Donnelly's 

 (1962) data as presented in the SPM (1984) (Figure 15). 



3-D Toe Berm Stone Tests Conducted With Spectral Waves 



28. All test conditions and test results discussed and reported up to 

 this point in the report have been relative to monochromatic test wave 

 conditions. Near the completion of this study, a spectral wave generator was 

 installed in the L-shaped wave basin; therefore, limited comparative spectral 

 tests were conducted. 



29. Two rubble-mound structure head and trunk plans were exposed to 

 spectral wave conditions for both 90-deg and oblique wave attack. Joint North 

 Sea Wave Project (JONSWAP) spectra with 7 3.3, slope parameters ct 1ow =0.07 

 for f less than f_ (where f refers to frequency and f_ refers to peak 

 spectral frequency), CT high =0.09 for f greater than f and the peak 

 period and water depth combinations shown in Table 7 were selected for testing 

 (see Figure 16 for a definition sketch). Goda and Suzuki's (1976) method was 

 used to resolve incident and reflected spectra at the sea-side toe of the 

 structures. The zeroth moment wave height H^ is defined as follows: 



H™ = 4(E) 1/2 (3) 



where E is a measure of total spectral energy and is equal to the area under 

 the curve on a spectral energy density versus frequency plot. Both the 

 measured H^ and the theoretical maximum H^ (Vincent 1984 and Hughes 1984) 

 based on depth limitation, are presented in Table 7. These R mo values gave 

 similar toe berm stability to that observed during monochromatic wave tests 

 conducted at the same wave period and water depth combinations. The U mo 



26 



