Rubble-mound breakwater designs should not be constructed 

 without physical model testing of some kind due to the limited 

 confidence of available analytical methods. 



The confidence of the key analytical tools for rubble-mound 

 breakwater design would be improved if current research were 

 continuously concentrated in the following specific areas with 

 probabilistic applications in mind: 



(1) Site conditions — Estimation of the long-term joint proba- 

 bility distribution F(H , T , t , d , (f, a) for a site 

 should be developed for application in estimating ex- 

 pected breakwater damages and the long-term distribution 

 of transmitted wave characteristics. 



(2) Armor stability — Standardized methods should be developed 

 for scale model testing of rubble-mound stability in nat- 

 ural irregular sea states. Improved analytical stability 

 prediction should be the goal of tests conducted by these 

 methods, explicitly including the effect of wave period, 

 storm duration, and other factors. Prototype verifica- 

 tion of analytical predictions should be attempted also, 

 particularly for new constructions where the design as- 

 sumptions are most thoroughly documented. 



(3) Mechanical stength of armor units — Prediction of armor 

 unit breakage by scale model tests should be developed in 

 order that both incipient damage and reserve stability 

 can be more accurately defined. 



(4) Breakwater damage prediction — The reserve stability of 

 a wide range of rubble-mound breakwater configurations 

 should be comprehensively tested by methods similar to 

 those developed to detect incipient damage. Improved 

 analytical prediction of reserve stability should be the 

 goal of these tests. 



(5) Runup on rubble-mound breakwaters — Improved instrumen- 

 tation and testing methods need development for measure- 

 ment of irregular runup on rough permeable slopes. A con- 

 certed effort should be made to define runup coefficients 

 for Equations 31 and 32 while concurrently investigating 

 means for improved analytical prediction of irregular 

 runup. The possibility of armor units designed both for 

 enhanced hydraulic stability and for efficient attenua- 

 tion of runup should be explored. 



(6) Wave transmission — The characteristics of irregular 

 waves transmitted by rubble-mound breakwaters should be 

 investigated. Improved analytical prediction of trans- 

 mitted wave characteristics as a function of incident ir- 

 regular wave characteristics should be the goal of this 

 research. 



72 



