where a and b are approximately: 



a = 43.75 CI - e-i9™) (4) 



1.56 



1 + e 



■19.5m 



C5) 



Values of d^, from equation C.3} can then be used in equation (2'} 

 when defining the wave setdown. 



Equation (2) uses the equivalent unrefracted deepwater wave height. 

 Hi, rather than the breaker height, H^ . Figure 2 gives values of 

 H^/H^ in terms of m and H^/gT^. 



Longuet-Higgins and Stewart (1963) have shown from an analysis of 

 Saville's (1961) data that, 



AS = 0.15 d2j (approximately) . (6) 



Combining equations (1) to (6) gives 



g 



1/2 (H')2 T 



O' 



0.15 d^ ^— — • , (7) 



64tt d^3/2 



where 



d^ = £ . (8) 



Lll^ 43.75 (1 - e-lS'") ^ 



1 + e-l9-5in gT2 



Figure 3 plots equation (7) in terms of S^/Hi versus Hi/gT^ for 

 slopes of m = 0.02, 0.033, 0.05, and 0.10, and is limited to values of 

 0,0006 < H^/gT^ < 0.027. 



Wave setup is a phenomenon involving the action of a train of many 

 waves over a sufficient period of time to establish an equilibrium water 

 level condition. The exact amount of time for equilibrium to be estab- 

 lished is unknown but a duration of 1 hour is considered as an appropriate 

 minimum value. The very high waves in the spectrum are too infrequent to 

 make a significant contribution in establishing wave setup. For this 

 reason, the significant wave height, Hg, represents the condition most 

 suitable for design purposes. 



The designer is cautioned not to confuse the wave setup with wave 

 runup. If an estimate of the highest point reached by water on the shore 



