FIND : The significant wave height at a 16.4-foot (5 meter) depth just off the 

 coast near the anemometer site. 



SOLUTION ; The fetch is found by averaging over a 24° quadrant since the body 

 of water is irregularly shaped. As shown in Figure 5, nine radials are 

 constructed at 3° increments and the average fetch length of 22 miles (36 

 kilometers) is found. 



The adjusted windspeed is found following the steps outlined previously: 



(a) Adjust wind from the 4-meter to the 10-meter level 



/in\V7 /10\^/'^ 

 Uio = { 7 ) ^Z " (z~) ^-"-^^ ^ -'-'^•-'- ™^ters per second 



(b) Adjust overland wind to overwater wind with R from Figure 3 



U^ = RUio = 1.25(17.1) = 21.4 meters per second 



(c) Correct wind for instabilities 



U^ = 0.71 U^^'^^ = 0.71(21.4)^-^^ = 30.7 meters per second 



(d) Correct for air-sea temperature difference with Rt from Figure 4 



U^ = Rt U^ = 1.17(30.7) =35.9 meters per second 



The dimensionless fetch, S, is 



,2> 



= II = (9.8 m/s^) (36.000 m) ^ 273 7 



U? (35.9 m/s)2 



The deepwater significant wave height and peak period are 

 Ho = 1.6 X 10-3 /lii2|0 (.33_g ^/g) ^ 3^3 meters 



35.9(273.7) '3 

 Tp = 3 5(9 " " 8) =6.80 seconds 



At a 5-meter depth 



Hq 3.5 '^ 



In Figure 2 at x = 273.7 and A/Vlq = 1.43 



gHe 



H = -~ = 0.012 

 U? 



and 



H U2 (0.12) (35.9)2 



Ho = = = 1.58 meters 



^ g 9.8 



13 



