characteristics. A group of waves, all of the same period, will travel in 

 deep water with a velocity known as the group velocity (Cg - 1.52T knots), 

 while any one wave in the group will travel with a velocity C - 3. OUT knots. 

 (Deep water waves are those that are moving in depths greater than one-half 

 their wave length) . 



$, Growth and Decay of Wind Waves . - An area of sea over which wind 

 has been blowing and generating waves is known as a fetch . The growth of 

 wavea within a fetch is governed by three factors: the speed of the wind (U), 

 the length of time this wind has been blowing, known as the duration (t), 

 and the length of the fetch (f). In a nongrowing fetch, a constant wind 

 speed will develop waves limited in height and period at first by the duration 

 of the wind, then by the length of the fetch. 



6. At an early stage of development of the waves, their heights or 

 periods at various points within the fetch will be distributed as shown by 

 the dashed line of Figure 1. At a later stage of development the distribu- 

 tion of wave heights or periods will be as given by the solid line of 

 Figure 1, 



Fetch Length 



WAVE DEVELOPMENT WITHIN A FETCH 

 FIGURE I 



