cot e 



R 2 /H s 



R 2 



R s /H s 



R s 



R/H s 



R 







(ft) 





(ft) 





(ft) 



2.50 



3.64 



21.8 



2.52 



15.1 



1.58 



9.5 



3.00 



3.49 



21.0 



2.43 



14.6 



1.56 



9.4 



2.75 



— 



21. 4 1 



— 



14. 9 1 



— 



9.4 1 



1 Interpolated value. 



The interpolated values in Table 2 should be corrected for scale effects 

 to yield the required answer. The scale correction factor for a slope of 1 

 on 2.75 is 1.125 (see App. A); therefore, 



R 2 = 21.4 (1.125) = 24.1 feet (7.35 meters) 



R s = 14.9 (1.125) = 16.8 feet (5.12 meters) 



R = 9.4 (1.125) = 10.6 feet (3.28 meters) 



A freebaord of 20.0 feet falls between R 2 and R s , so the structure 

 crest would not be overtopped frequently, probably by less than 10 percent 

 of the waves. It is, therefore, expected that the volume of overtopping 

 would not be great. 



It is difficult to determine how high a smooth structure would have to 

 be to prevent all wave overtopping but a reasonable estimate would be 



Rmax ~ R 2 + H s 



where Rmax is the elevation of the maximum runup. 



*************** EXAMPLE PROBLEM 2*************** 



This example illustrates how to calculate the approximate lower limit of 

 rundown. 



GIVEN : A plane, smooth 1 on 2.50 slope is subjected to irregular wave action. 

 The significant wave height, significant wave period, and water depth at the 

 toe of the structure are 7.0 feet (2.13 meters), 8.0 seconds, and 30.0 feet 

 (9.14 meters), respectively. 



FIND: Rdgs for the above conditions; this is the approximate lower limit of 

 wave rundown. 



SOLUTION : The period of peak energy density is 



T p = 1.05(T S ) = 1.05 x 8.0 = 8.40 seconds 



and the surf parameter is 



c = 1 ; 1 



(Hg/Lo) 1 / 2 cot 6 {7.0/[32.2 x (8.4) 2 ] /2^ } (2.5) 



