1 Introduction 



Background 



High sea waves tend to appear in groups rather than individually. Be- 

 cause of the nature of wave grouping, it appears that it may be an impor- 

 tant influence on the stability of rubble-mound structures. 



A succession of high waves that exceeds some arbitrary threshold value 

 (typically mean or significant wave height) is called a run of high waves, 

 and the number of waves in this run is the run length. The total or com- 

 plete run is the combination of the run of high waves followed by the run 

 of low waves. Reference to a wave group assumes that a run of high 

 waves is intended. In the present investigation, a group of waves is de- 

 fined as three or more successive waves that have heights equal to or ex- 

 ceeding the significant wave height of the entire test run. Also, the 

 grouping intensity (GI) is defined as the number of these groups per hour 

 of test waves. 



Purpose of Study 



The purpose of the present investigation is to obtain a better under- 

 standing of the effects of wave grouping on the stability of stone armor 

 when used on breakwater trunks. 



Approach 



Previous breakwater stability investigations conducted by Carver 

 (1983) and Carver and Wright (1991) have shown that relative depth (d/L) 

 and relative wave height (H/d) are two of the most important dimension- 

 less variables influencing breakwater stability with minimum stability oc- 

 curring at the lower values of d/L and higher values of H/d, i.e., longer 



Chapter 1 Introduction 



