for Sjj is not needed. The reason for this is that laboratory measurements 

 of wave runup are taken in reference to the Stillwater level and already in- 

 clude the wave setup component. 



Figure 3-49b illustrates a more complex situation involving wave setup. 

 Here we have a beach fronted by a wide shelf. At some distance offshore the 

 shelf abruptly drops off into the deep water. As waves approach the beach, 

 the larger waves in the spectrum begin to break, at the seaward edge of the 

 shelf and a setup is produced. The increase in water level produced by this 

 setup allows waves larger than would exist if based on the normal Stillwater 

 level to travel shoreward until they break on the beach. Calculations of wave 

 runup on the beach would include the additional wave setup effects from the 

 breaking of these smaller waves. 



a. Wave Setup Due to Monochromatic Waves . Theoretical studies of wave 

 setup have been made by Dorrestein (1962), Fortak (1962), Longuet-Higgins and 

 Stewart (1960, 1962, 1963, 1964), Bowen, Inman, and Simmons (1968), Hwang and 

 Divoky (1970), James (1974), and Goda (1975). Theoretical developments can 

 account for many of the principal processes, but contain factors that are 

 often difficult to specify in practical problems. 



The computation of wave setup can be an important part of a thorough 

 design effort requiring water level estimation. For major engineering 

 structures such as nuclear powerplants it is quite important to consider all 

 possible causes of water level rise. Wave runup computations alone will 

 usually be sufficient, but in cases similar to that shown in Figure 3-49b, 

 where large waves break offshore, an increase in the Stillwater level on the 

 berm or reef should be considered in determining the limit of wave runup. 



In studies of coastal flooding by hurricanes, the effects of wave setup 

 should be considered in the water level estimate. The procedure presented can 

 be used to compute the wave setup for the cases shown in Figure 3-49 . 



R.O. Reid (Texas A & M University personal communication, 1972) has 

 suggested the following approach for estimating the wave setup at shore, using 

 the Longuet-Higgins and Stewart (1963) theory for the setdown at the breaking 

 zone and solitary wave theory. The theory for setdown at the breaking zone 

 indicates that 



% = 372- (3-74) 



64 TTd^' 



where 



Sji = the setdown at the breaking zone 



T = the wave period 



\{L = equivalent unrefracted deepwater significant wave height 



d^ = the depth of water at the breaker point 



g = the acceleration of gravity 



3-101 



