FIND : The height to which the riprap must extend above the design water level 

 to prevent being exceeded by the runup . 



SOLUTION : It is necessary to compute d s /H^ to determine which figure to use 

 in Stoa (1979). Since there is no clearly defined toe for this structure, a 

 water depth of one-half the deepwater wavelength will be used (this is the 

 depth where the waves first "feel" the bottom) 



d c = 0.5L n = 



- 0-5 x 9.80 x (4.7) 2 



6.28 



= 17.24 meters (56.5 feet) 



therefore, 



dg 

 Ho ' 



17.24 

 1.52 



11.3 



which leads to using Figure 4 (Fig. B-3 in Stoa, 1979). To use Figure 4, 

 the wave steepness parameter is required, so 



gT 2 



1.52 



9.80 x (4.7) : 



= 0.0070 



3 4 56789 10 

 Structure slope (cot 8) 



Figure 4. Relative runup for riprap slopes; d s /HQ = 8.0; 

 Hq/Kj- - 2.8. Use this figure also for 

 d s E > 8.0 (from Stoa, 1979). 



17 



