caused by irregular waves. However, several of these methods are based on 

 regular (monochromatic) wave experiments and theory. In a monochromatic wave 

 field, all waves have the same height and period. This is the type of wave 

 train made by many laboratory wave generators and approximated in nature by 

 swell from distant storms. An irregular wave field can be thought of as many 

 waves of different heights and periods traveling in different directions on 

 the same body of water. Coastal engineers often represent irregular seas with 

 a significant wave height H s or H^? , which is defined as the average of 

 the one-third highest waves. Another definition of significant wave height is 

 the spectral significant wave height H mo (Shore Protection Manual (SPM) 

 1984). For engineering purposes, it is significant to know how much over- 

 topping will be caused by an irregular sea with a given significant wave 

 height (significant wave height is only one of the parameters used to describe 

 an irregular sea). 



5. Comparing the existing methods of estimating overtopping with labo- 

 ratory or field data would be an optimal way to evaluate the methods. Unfor- 

 tunately, no comprehensive data set of overtopping rates caused by realistic 

 irregular waves has been published. Therefore, it cannot be confidently 

 stated that one of the methods predicts wave overtopping quantities better 

 than the others. However, this report will evaluate the assumptions made in 

 the derivation of each method and examine the design situations for which each 

 method was developed. 



6. Part II of this report briefly describes four methods of estimating 

 wave overtopping caused by irregular waves, presents an example of how to use 

 each method, and discusses the effect of assumptions made in the derivation of 

 each method. Since the estimation methods were not developed for identical 

 situations, Part III of this report outlines which methods can be used for 

 which design situations and compares the results of the methods when more than 

 one method can be used. The methods are compared with the very limited, pub- 

 lished laboratory and field data. Part IV briefly discusses the effects of 

 wind speed and direction, angle of wave incidence, and varying still-water 

 level (SWL) on wave overtopping. 



7. This report does not explain to the design engineer how to choose 

 all the parameters needed to apply these overtopping methods. The selection 

 of water levels and wave characteristics for the design of coastal structures 

 is beyond the scope of this study. These parameters will be considered as 

 "known input parameters." 



