The runup reduction factor, r, for rubble-mound breakwaters with high 

 cores is 0.52 (see App. B) and the scale-effect correction factor is 1.06 

 (see App. C) so R2 for the breakwater is 



R 2 (breakwater) = 51.3(0.52) 1.06 = 28.3 feet (8.63 meters) 



R s and R are found in a similar manner to be 



R s (breakwater) =20.0 feet (6.10 meters) 



R (breakwater) =12.2 feet (3.72 meters) 



These calculations indicate that if the freeboard were 28.3 feet only 2 per- 

 cent of the waves with a H s = 15 feet and T s = 12 seconds spectrum would 

 overtop the structure while a freeboard of 12.2 feet would allow about half 

 the waves to overtop. A freeboard equal to R s , i.e., 20 feet, will satisfy 

 the condition of only occasional wave overtopping since about 13 percent of 

 the waves would be expected to overtop the breakwater. 



*************************************** 



VI . SUMMARY 



Equations and curves are presented for computing three runup parameters and 

 one rundown parameter for plane, smooth slopes exposed to irregular wave condi- 

 tions where d s /H s > 3. These parameters are R2 , the elevation exceeded by 

 only 2 percent of the runups; R s , the average runup of the highest one-third 

 of the wave runups; R, the mean runup of all the runups; and Rdgs, the 

 depth below the Stillwater level which is just greater than 98 percent of the 

 rundown. Example problem 1 illustrates the use of equation (2) in computing 

 the rundowns, parameters, and the method of interpolation for runup on slopes 

 not specifically covered in this report. Example problem 2 illustrates the 

 method of computing rundown. Example 3 illustrates how the study results for 

 smooth slopes can be applied to rough and porous slopes, in this case to com- 

 pute the desired freeboard for a rubble-mound breakwater. 



