c. No nbrea ki ng Waves . Since statistical hindcast wave data are normally 

 available for deepwater conditions (d > L /2) or for depth conditions some 

 distance from the shore, refraction analysis is necessary to determine wave 

 characteristics at a nearshore site (see Ch. 2, Sec. Ill, WAVE REFRACTION). 

 Where the continental shelf is broad and shallow, as in the Gulf of Mexico, it 

 is advisable to allow for a large energy loss due to bottom friction (Savage, 

 1953), (Bretschneider, 1954a, b) (see Ch. 3, Sec. VII, HURRICANE WAVES). 



General procedures for developing the height and direction of the design 

 wave by use of refraction diagrams follow: 



From the site, draw a set of refraction fans for the various waves that 

 might be expected (use wave period increments of no more than 2 seconds) and 

 determine refraction coefficients by the method given in Chapter 2, Section 

 III, WAVE REFRACTION. Tabulate refraction coefficients determined for the 

 selected wave periods and for each deepwater direction of approach. The 

 statistical wave data from synoptic weather charts or other sources may then 

 be reviewed to determine if waves having directions and periods with large 

 refraction coefficients will occur frequently. 



The deepwater wave height, adjusted by refraction and shoaling coef- 

 ficients, that gives the highest significant wave height at the structure will 

 indicate direction of approach and period of the design wave. The inshore 

 height so determined is the design significant wave height. A typical example 

 of such an analysis is shown in Table 7-1. In this example, although the 

 highest significant deepwater waves approached from directions ranging from 

 W to NW , the refraction study indicated that higher inshore significant 

 waves may be expected from more southerly directions. 



The accuracy of determining the shallow-water design wave by a refraction 

 analysis is decreased by highly irregular bottom conditions. For irregular 

 bottom topography, field observations including the use of aerial photos or 

 hydraulic model tests may be required to obtain valid refraction information. 



d. Bathjmietry Changes at Structure Site . The effect of a proposed 

 structure on conditions influencing wave climate in its vicinity should also 

 be considered. The presence of a structure might cause significant deepening 

 of the water immediately in front of it. This deepening, resulting from scour 

 during storms may increase the design depth and consequently the design 

 breaker height if a breaking wave condition is assumed for design. If the 

 material removed by scour at the structure is deposited offshore as a bar, it 

 may provide protection to the structure by causing large waves to break 

 farther seaward. Experiments by Russell and Inglis (1953), van Weele (1965), 

 Kadib (1962), and Chesnutt (1971), provide information for estimating changes 

 in depth. A general rule for estimating the scour at the toe of a wall is 

 given in Chapter 5. 



e. Summary — Evaluating the Marine Environment . The design process of 

 evaluating wave and water level conditions at a structure site is summarized 

 in Figure 7-6. The path taken through the figure will generally depend on the 

 type, purpose, and location of a proposed structure and on the availability of 

 data. Design depths and wave conditions at a structure can usually be 

 determined concurrently. However, applying these design conditions to 

 structural design requires evaluation of water levels and wave conditions that 



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