PART II: WAVE RUNUP AND OVERTOPPING OF BREAKWATERS AND JETTIES 

 CAUSING EXCESSIVE WAVE ACTION ON THE LEE SIDE 



5. Numerous methods have been developed to estimate transmitted wave 

 heights on the lee side of rubble-mound and caission structures. Most of the 

 methods suffer from one or more of the following limitations: 



a. They are so highly idealized that they are not useful for 

 solving "real world" problems. 



b. They are applicable to only part of the problem, i.e., they only 

 consider the wave energy transmitting through the structure or 

 only consider wave transmission by overtopping. 



c. They are inherently so complex that they are difficult to use 

 and understand; lack of understanding undermines confidence and 

 makes it difficult to evaluate results. 



Another problem common to all approaches is that they were not developed to 

 help guide repair or rehabilitation efforts. As an example, Fuchs ' equation 

 (Johnson, Fuchs, and Morison 1951) could potentially be used to estimate the 

 breakwater's crest height required to reduce wave transmission to a desired 

 level. In principle this calculation would provide an estimate of the amount 

 of repair necessary to rebuild the crest height high enough to reduce trans- 

 mission to an acceptable level. However, Fuchs' equation is only applicable 

 to submerged structures and then treats them like a plate so that the influ- 

 ence of the width or permeability cannot be investigated. Still Fuch's equa- 

 tion, like a number of other highly idealized approaches to estimating wave 

 transmission, provides useful conceptual insight if not solutions to real 

 problems. In the following discussion a less idealized transmission model 

 will be used to illustrate how a model might be used to guide repair or re- 

 habilitation work to reduce wave transmission. 



6. Findings from a research study of low-crested breakwaters will be 

 used as an example of how a wave transmission model might be applied to reha- 

 bilitation efforts. The transmission model was developed by Ahrens (1986) to 

 predict the transmission of wave energy over and through reef breakwaters. 

 Advantages of this model are that it: 



a. Was developed from a large number of laboratory tests having a 

 wide range of irregular wave, conditions. 



b. Can be used for both submerged and subaerial rubble mounds. 



c. Accounts for wave transmission both over and through the 

 structure. 



