PART IV: OTHER PARAMETERS THAT AFFECT OVERTOPPING 

 Onshore Winds 



65. Thus far, several parameters which affect overtopping have been 

 ignored for the sake of simplicity. Onshore winds should increase the over- 

 topping rate at a seawall. The SPM recommends an unverified wind correc- 

 tion. For onshore winds, the correction varies from 1 to 3.2. Owen (1980) 

 uses the SPM wind correction factor; the other two methods do not address the 

 problem. However, it must be realized that this equation is merely a rough 

 engineering estimate of a very complex phenomenon. Gadd et al. (1984) discuss 

 some qualitative trends in the wind effect and conclude that more data are 

 needed to improve upon the SPM correction. 



Angle of Wave Attack 



66. Very little information exists concerning the effect that angle of 

 wave attack has on overtopping. In the absence of data, engineers have 

 usually assumed that overtopping is maximum when waves hit the structure head- 

 on, i.e. perpendicularly, and tapers off to zero as the angle of attack 

 lessens. However, Owen (1980) found that overtopping is maximum not when 

 waves approach the structure perpendicularly, but at an angle of 15°. During 

 his smooth-slope overtopping tests, Owen investigated angles of attack of 

 (perpendicular), 15, 30, 45, and 60°. The effect of angle of attack for one 

 structure slope is shown in Figure 19. The overtopping at 30° was similar to 

 that at 0°. Figure 19 shows the results held for various freeboards. Owen 

 (1980, 1982) has no explanation for the results shown in Figure 19. However, 

 similar results have been seen by Tautenhain, Kohlhase, and Partenscky (1982) 

 for monochromatic wave runup. Until more data are available to better define 

 this phenomenon, care should be taken to not assume too much overtopping 

 reduction for oblique angles of wave attack. 



Varying Water Level 



67. One of the most important parameters in overtopping estimation is 

 the water depth at the structure. For a given structure, increasing the water 



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