Fy = 3.34 feet and T = 351 seconds . 



NOTE. --For a sandy bottom, £ -p = 0.01, the wave would have increased to a 

 height of approximately 4.26 feet, a 42-percent increase from the 

 initial wave height of 3 feet. For thick stands of tall grass, the 

 predicted increase in wave height is only 11 percent using the approx- 

 imate method of solution discussed in this report. 



*************** EXAMPLE PROBLEM 2************* 



GIVEN : A coastal area is flooded by a storm surge so that the water depth 

 over the area is 10 feet (3.05 meters). The actual fetch across the 

 area, in the direction of wave travel, is 3,000 feet (914 meters). The 

 area is covered with thick stands of tall grass and a small to moderate 

 amount of brush or low, bushy trees in an even distribution. The wind- 

 speed is 90 miles per hour (132 feet per second or 40.2 meters per 

 second) and the initial wave height at the seaward edge of the area is 

 6 feet (1.83 meters); the wave period is 4.5 seconds. 



FIND : The decayed wave height at the end of the fetch. 



SOLUTION : From the long dashline in Figure 1, for the windspeed of 90 

 miles per hour and the water depth of 10 feet, 



M = 52 - 2 x 10 = 0.0185 

 U 2 (132) 2 



giving (at the intersection of the above line with the long dashline) 

 £j = 0.0075 



so that the maximum significant wave height 



0.0075 U 2 0.0075 (132) 2 . , _ 



FL_, = = 5^ '— =4.1 feet . 



sm g 32.2 



From equation (10), 



F^ = 0.78d = 0.78 (10) = 7.8 feet 



and from equation (9) , the fractional reduction is 



% ' H i 7.8 - 6 



&i = = b 0.486 . 



Km ~ H sm 7.8 - 4.1 



From equation (11), the equivalent initial wave height 



H^g = R£ H sm = 0.486 x 4.1 = 1.99 feet ; 

 from Figure 1, for 



32 



