INCIDENT WAVES 

 TRANSMITTED WAVES 



Figure 199. 



0.5 1.0 1.5 2.0 2.5 



FREQUENCY [l/SEC] 



Effect of Bowley wave barrier concept of 

 floating breakwater on Pierson-Moskowitz 

 spectrum (after Bowley, 1974). 



XIII. RESERVOIR APPLICATION FLOATING BREAKWATERS 



Reservoir marinas often require breakwaters that can function over a large 

 range of water levels. The water surface elevation of a flood control reser- 

 voir may fluctuate 50 feet or more because of necessary drawdown during the 

 summer and autumn seasons. An adequately designed breakwater must be capable 

 of following the water surface elevation, without undue stress in the moor- 

 ings, and function at all elevations. Typical design criteria include waves 

 up to 60 feet long, periods up to 4 seconds, and heights up to 5 feet; how- 

 ever, the Task Committee on Small-Craft Harbors (1969) recommended that wave 

 heights not exceed 1 foot in the mooring areas. Hay and Skoda (1967), Chen 

 (1969), and Chen and Wiegel (1969, 1970) addressed the problem of developing 

 floating breakwater designs especially for reservoir applications. The 

 problems arising from the necessity of mooring floating structures were 

 approached from the concept of increasing the effective mass or moment of 

 inertia with entrained water, and Chen and Wiegel (1969) conducted experi- 

 mental investigations. Several hybrid types of moored floating structures 

 which combine two or more previously investigated concepts were formulated. 

 These structures are reasonably small compared with the longest design wave- 

 length, and are capable of reducing the highest design incident wave height to 

 less than 1 foot in the lee of the breakwater. 



257 



