of occurrance of .the latt-3r . i is th.? avsrage Freqiyincy (in %) in the 

 direction of th3 fabch-, aii'i 5 is an avara^e definsd ii3i. 



s =■• -,/-_'^'^ 



for each fetch direc"C;ian= (S^ is the speed corresponding to -any 

 frequency F) 



f-funch-Petersen explains the formula in the following manner » 

 For rJeap-Tfater waves (throchoidal waves) j the height of the vraves in- 

 creases proportionally with the speed of the Trind, and as mentioned 

 before 3, the depth of the water where the attack on the bottorri starts 

 is proportional to the height of the wavec From this it follows that 

 this latter water depth also must be proportional to the speed of the 

 windo The speed of the ground-water vfave is proportional to the 

 square root of the water depth; furthermore^ the influence of the 

 wave on the bottom of the ocean obviously must be proportional to the 

 square of the speed of the wave 5 and in accordance v^'ith the above dis- 

 cussions to the depth of the water. Subject to conditions of equal 

 slope of the bottom the area between the coast line and the line where 

 the waves break (i.e„ the zone of material drift) will be proportional 

 to the depth of th3 water on the line where the wave breaks o Since 

 the influence of the Tjave on the bottom , as well as the area in which 

 this influsnce occijirSj are proportional to the depth of the v/ater^ 

 then the quantity of material put into motion by the wave, can be set 

 proportional to this depth squared, or to the speed of the wind squared. 

 still the mater jal-transport must be proportional to time, that is 

 to the frequency of the wind. Finally the height of the wave^ vj-hich 

 is Cj iff, and tte obliquity, cos a , must be added o With the notation 

 given in Fi^Tire 5j we have, for any chosen direction of the wind, 



t = k c F o S^ o A/f . cos (X-Aq) 



and for tte resulting material-transporting power components in all 

 directions of the wind 



T = X Z (F c S^ ^ff „ cos(X-A(p ) 



Since weather -forecasting stations usually give wind data for 8 

 directions of the compass, it is practical to use these for our 

 calcuations. If we know the values of F and S in these directions, 

 ve can y;ith a rather high degree of accuracy draw the continuous 

 curve of F and S in the polar-coordinates plot shown as Figure 5= 

 However, it is suffuciently correct to use the average values for 

 each compass-direct ion. It can be seen from Figure 6, that if the 

 coast line coincides -vilth the mid-direction between two of these 8 

 'lirections, we will only have to sumnarize 4- sectors, whereas we 

 must use 5 sectors in all other cases. To summarize the two utm.ost 

 o-.-'ctors, we must add ths factors '^4.'" an'^ f'// .^o ,) > where a is 

 the angle between the coast line and the closest mid-dire ctiono This 

 detsimilnation can be made by calculation, but it is m.ore illustrative 

 to set it up in a diagram, using the components which are determined 



