and 



^ = 5.37 X 10^^ 1 (3-41) 



The wind-stress factor U. (adjusted windspeed) is obtained by 



estimating the surface wind U in meters per second via Chapter 3, Section 



1 .23 

 IV and then setting U. = 0.71 U * . Each figure is plotted for a constant 



water depth d . Linear interpolation between figures is sufficiently 

 accurate for determining intermediate wave heights and periods. For water 

 depths greater than 15 meters (50 feet) and less than 90 meters (300 feet) , 

 use equations (3-39) to (3-41). For depths greater than 90 meters (300 feet), 

 the revised deepwater forecasting equations should be used. 



The minimum duration t has been added to the shallow-water forecasting 

 curves to simplify determining the wind-stress factor Ua . Waves with 

 periods less than a specified value are noted as deepwater waves on each 

 figure. The duration equation used, therefore, is a transposed, simplified 

 approximation of the deepwater duration equation. 



*************** EXAMPLE PROBLEM 5*************** 

 GIVEN: Fetch length F = 24.4 km (80,000 ft) 



Wind-stress factor U^ = 22 m/s (50 mi/hr) 



Constant depth d = 11 m (35 ft) 

 FIND : Wave height H^ 



Wave period T 

 SOLUTION; 



From Figure 3-33a or equation (3-39) and (3-40) 



Hg = 1.5 m (4.9 ft) 

 and 



T = 4.4 s 



*************************************** 



2 . Propa gation Over Flooded, Ve getate d Land . 



When waves travel across a shallow flooded area, the initial heights and 

 periods of the waves may increase; i.e., when the wind stress exceeds the 

 frictional stress of the ground and vegetation underlying the shallow water. 

 The initial wave heights may decay at other times when the frictional stress 

 exceeds the wind stress. 



Camfield (1977) presents an approximate method for estimating the growth 

 or decay of wind waves passing over areas with high values of bottom fric- 

 tion. It is assumed that the high friction values can be accounted for by 



3-66 



