PART II: BASIC DESIGN PRINCIPLES 

 Design Criteria 



8. There is a well-known tendency for subjective judgments to creep 

 into supposedly systematic project planning endeavors in the earliest phases. 



A proven method to order your thinking in the conceptual phase of a project is 

 to first thoroughly define the problems and opportunities at the site in terms 

 of desirable goals to be achieved. This has long been the first step in the 

 civil works planning process as practiced by the Corps. Two types of design 

 criteria or "planning objectives," as stated in Corps planning guidance (Board 

 of Engineers for Rivers and Harbors 1985 and Water Resources Council 1983), 

 can be identified at this point relative to the function of a breakwater as a 

 wave barrier. The first, and most familiar, is a criterion which defines the 

 structure's ability to withstand the effects of extreme storms without itself 

 suffering significant damages. This type of criterion can be referred to as 

 the "structural integrity" or "survival" criterion. The second type, referred 

 to as the "functional performance" criterion, deals with the effectiveness of 

 the structure at its intended function which is to provide protection from 

 waves. 



9. The structural integrity criterion determines the breakwater's life- 

 cycle costs to the extent that a certain level of investment is necessary to 

 prevent damages from an extreme event. There will always be a finite proba- 

 bility that any storm, no matter how extreme, will be exceeded in intensity, 

 so this criterion also determines the expected repair costs during the proj- 

 ect's life. The most extreme sea state in which a particular breakwater de- 

 sign will suffer no damages cannot, in practice, be precisely defined, as will 

 be discussed later. The statement of a structural integrity criterion should 

 be phrased with this in mind. It should be stated in terms of the desired 

 effect, that is, prevention of breakwater damages (and associated repair 

 costs). An example would be "damages to more than 5 percent of the breakwater 

 armor will occur with less than 2 percent probability per year." There are, 

 of course, numerous complications in achieving such a goal, including defini- 

 tion of the types of possible damages and determination of the combined proba- 

 bility per year of the physical parameters (wave height, wave period, wave 

 direction, water level, storm duration, and others) which could cause them. 



