and the maximum runup using the best fit coefficients in equation (8) gives 

 = R s f^pi J 1.41(1.64) = 2.31 meters (7.58 feet) 



Rma 



The method used in ETL 1110-2-221 to compute the maximum runup assumes a 

 constant 50 percent greater than the significant runup; therefore, 



Rmax = R s O-- 5 ) = 1-47(1.5) = 2.20 meters 

 Table 2 summarizes the results of this example problem. 



Table 2. Example problem 3 summary. 



Method 



\iax 



(m) 



(ft) 



Stoa (1979) 

 This report 

 ETL 1110-2-221 



2.20 



2.31 



J 2.20 



7.22 

 7.58 

 7.22 



The three methods yield similar results and possibly the highest value 

 of R max should be chosen to be conservative. 



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



In computing the maximum runup, the assumption is that 



Rmax ^max 



Rs 



H f 



This assumption is not intended to suggest that the maximum runup is caused by 

 the maximum wave but only to provide a reasonable factor by which to obtain 

 Rmax from a typical value of runup such as R s . If relatively shallow water 

 fronts the structure there will be truncation of the wave height distribution 

 due to depth-limited and steepness-induced breaking which should cause a cor- 

 responding truncation in the runup distribution. Using a constant factor, 

 such as 1.5, to estimate the maximum runup from the significant runup (by the 

 method in ETL 1110-2-221) may overestimate Rmax f° r shallow-water conditions. 

 In example 4, a shallow-water situation where there is truncation of the wave 

 height distribution due to wave breaking will be considered. The three methods 

 used in example 3 are also used in example 4 to show comparative answers; the' 

 problem requires the use of Table 3 which gives the ratios Hmax/K s and H s /Hq 

 based on the Goda (1975) model. 



19 



