Once these waves have been generated ty a -mind disturbance j, they 

 may leave the area of the disturbance and travel for hundreds or even 

 thousands of miles before being interrupted ty a land masso In fact, 

 most of the waves noted along our ocean beaches are generated at a 

 distance o 



lUiere are several descriptive terms for water waves j, among them 

 are progressive waves j, stationary waves, and solitary waves o So far 

 as beach action is concerned we will confine ourselves to a discussion 

 of progressive oscillatory waves o Hhese waves are characterized by a 

 progressive movement of successive wave crests in a single direction 

 whereas the water particles themselves oscillate in an essentially cir= 

 cular path when in deep watero In effect tiiis means that the wave form 

 moves forward but there is little or no progressive forward movement of 

 the water particle So Hie waves themselves are described by the "length" 

 from crest to crestj, the ''height" from trough to crest^ and the "periodj" 

 which is the time interval between the arrival of successive crests at 

 a stationary pointo 



As the wave moves into shallow waters, the bottom begins to affect 

 the form and mechanics of the wave© Initially^, the circular paths of 

 the water particles are gradually changed into elliptical paths and the 

 height and length of the wave are alteredo Finally j, the wave reaches 

 a depth so-shallow that the mechanics of the fluid motion make it iiB= 

 possible to transmit the wave form any f urtherg at this point the wave 

 combs over and breaks o 



In order to obtain a picttire of these ocean waves 5 let us mentally 

 follow a wave from the time of its inception in the open sea until it 

 destroys itself by breaking on some distant shore o Suppose a meteorol- 

 ogical disturbance over the North Atlantic generates a wind of 26 knots 

 blowing for some 24. hours over a fetch of 300 nautical miles ^ Bnpiri- 

 cal relations which have been established show that these conditions 

 would generate waves which would leave the storm area ?d.th a height of 

 about 15 feetg a length of about 300 feetj, and a period of about 7o5 

 seconds o 



One way of describing this wave is by length=height (L/H) ratio 

 or steepness ratio o For the present case, the ratio would be 20 o The 

 mechanics of the fluid make it impossible to have an L/H ratio less 

 than about 7o Ihe shorter ratio Sj, 7 through about 35, are character- 

 istic of waves in or near their generating area and such waves are 

 called storm waves « 



As the waves leave the generating area they begin to lose energy 

 due to atmospheric resistance o This results in a change in the shape 

 of the wavej specifically a decrease in hei^t and an increase in 

 lengtho Let us suppose that our 15=foot wave in the above example 



10 



