characteristics, and wave climate, must first be quantitatively defined. It 

 is assumed that many of these conditions have been already defined in a master 

 planning effort which identified the tentative need for a breakwater and its 

 most promising alignment. The water level and wave climate are the most crit- 

 ical considerations for this optimization procedure, specifically the estima- 

 tion of the annual cumulative probability distribution F (Hg , T , t , (p , 

 o , d). Current practices typically require planners and designers to esti- 

 mate F(Hg) for a limited range of wave directions 4) affecting the site of 

 the breakwater or, at best, to define a wave rose and then deal with the mar- 

 ginal distribution of wave heights for one sector. Design values of wave pe- 

 riod T , storm duration t , directional spreading o , and depth d asso- 

 ciated with a given wave height are typically subjectively determined. The 



mathematical estimation of F(H , T ) is becoming more common, however, with 



s p 



the availability of hindcast data bases of wave information (Corson et al. 

 1981). 



87. The Extremal Type I distribution for F(H ) , based on H^ values 

 above an extreme threshold value, is recommended in this procedure for designs 

 where hindcast information or other comparably long records of wave data are 

 available. A Weibull distribution of extremes is a workable alternative. Ap- 

 plication software program WAVDIST for estimating Extremal Type I and Weibull 

 significant wave height distributions has been documented in a Coastal 

 Engineering Technical Mote (CETN),* and an example of its use in a design 

 problem is presented in Andrew, Smith, and McKee (1985). 



Step 2--estimate ex- 

 pected economic losses 



88. Estimation of losses or "user costs" due to wave attack requires 

 derivation of a site-specific relation in which losses are a function of inci- 

 dent wave height. The typical harbor mooring area or cargo transfer area is 

 unaffected by waves below a certain height H, which might be on the order 

 of 1 m. The total disruption of the port or harbor area at the other extreme, 

 by the worst conceivable wave attack, is also possible to estimate as a prac- 

 tical upper limit to losses ^^^slx • These two values are useful in that they 



* US Army Engineer Waterways Experiment Station, Coastal Engineering Research 

 Center, in preparation, "Estimation of Extremal Significant Wave Height Dis- 

 tributions: Computer Program WAVDIST (MACE-17)," Coastal Engineering Tech- 

 nical Note, Vicksburg, Miss. 



58 



