where 



L D = the Airy wave length calculated by using the water depth at the toe 

 of the structure 



d = the period of peak energy density, T 



Runup is computed using the formula 



R 



max aS , ,_ . 



(5) 



H ~ 1.0 + bS 

 mo 



where 



Rjjj = elevation of maximum wave runup 



S = surf parameter defined by either Equation 3 or 4 depending on 

 the prediction method selected 



a and b = dimensionless runup coefficients determined by regression 

 analysis 



Equation 5 has a form which is especially convenient and logical for predict- 

 ing wave runup on rough porous slopes as shown by Ahrens and McCartney (1975), 

 and, subsequently, by Seelig (1980) and US Army Corps of Engineers (1985). For 

 the NCE data, using the modified surf parameter defined by Equation 4, the 

 coefficients in Equation 5 were found to be a = 1.062 and b = 0.153 • 



15. By using the coefficients given above, Equation 5 does a good job of 

 predicting R,j, ax for both the NCE and SAJ studies. Figure 8 shows the 

 predicted values of Kr. ax versus the observed values of \ iax by using dif- 

 ferent symbols to identify the two studies. The good fit to the NCE data is 

 gratifying considering the problem related to estimating the H mo at the toe 

 of the structure. The good fit to the SAJ data is somewhat surprising consid- 

 ering that the thickness of the armor layer for the SAJ test was considerably 

 thinner than the armor layer used in the NCE tests. In addition, the struc- 

 tural slopes tested for SAJ were 1 on 3 and 1 on 4 compared with a slope of 



1 on 2 for the NCE tests. These findings indicate that the maximum runup may 

 not be too sensitive to the armor-layer thickness, and that the surf parameter 

 properly accounts for differences in the structural slopes. It should also be 

 recalled that the runup coefficients were obtained from the NCE study so that 

 the SAJ data provide a rather severe test for the runup model's predictive 

 ability. 



16. By lumping the data from the two studies together, somewhat better 



12 



