SOLUTION : From Figure 3-27 for constant depth, d = 35 feet, 



for 



F = 80,000 feet, 

 and 



U = 50 mph. 

 Then 



H = 5.9 feet, say 6 feet, 

 and 



T = 5.1 seconds, say 5 seconds. 



***************************** ***k**f* 



3.62 DECAY IN LAKES, BAYS, AND ESTUARIES 



Section 3.33. Decay of A Wave Field applies to water aroa^^ contijiuous 

 with land as well as those in the open ocean. Most fetches in inltu'.d 

 waters will be limited at the front and at the rear by ^ l.ind m;i<s .uul 

 decay distances will usually be relatively small or nonexistent. 



3.7 HURRICANE WAVES 



When predicting wave generation by hurricanes, the determination of 

 fetch and duration from a wind field is more difficult than fur more normal 

 weather conditions discussed earlier. The largo changes in wind speed and 

 direction with both location and time cause the difficulty. Estimation of 

 the free air wind field must be approached through matliematical models, 

 because of the scarcity of observations in severe storms. However, the 

 vertical temperature profile and atmospheric turbulence characte;-istics 

 associated with hurricanes differ less from one storm to another than for 

 other types of storms. Thus the relation between the free air winds and 

 the surface winds is less variable for hurricanes than for other storms. 



3.71 DESCRIPTION OF HURRICANE WAVES 



In hurricanes, fetch areas in which wind speed and direction remain 

 reasonably constant are always small; a fully arisen sea state never 

 develops. In the high-wind zones of a storm, however, long-period waves 

 which can outrun the storm may be developed within fetches of 10 to 20 

 miles and over durations of 1 to 2 hours. The wave field in front, or to 

 either side, of the storm center will consist of a locally generated sea, 

 and a swell from other regions of the storm. Samples of wave spectra, 

 obtained during hurricane Agnes, 1972, are shown in Figure 3-31. Most 

 of the spectra display evidence of two or three distinct wave trains; thus, 

 the physical implications of a signifiaant wave period is not clear. 



Other hurricane wave spectra computed with an analog spectrum analyzer 

 from wave records obtained during Hurricane Donna, 1959. have been published 

 by Bretschneider (1963) . Most of these spectra also contained two distinct 

 peaks . 



3-52 



