If new energy is not transferred to the watsr from the wind^ the 

 wave TTfill lose height because of internal friction » If energy is 

 transferred from the wind the shape of the wave will be maintained^ 

 or possibly^ increased. The wave influenced by the wind is a little 

 different from tte trochoid^ being mors flat on tte backside and more 

 steep in front. If the influence of the wind is verystrong^ the wave 

 can fall forward (white caps)« However, the wind can only blow the 

 waves up tc a certain size, and the size is different according to 

 the nsture of the different oceans. 



It is obvious that the vrave iivill change if the depth of tte water 

 decreases so much that the wave will reach the bottom. If the wave 

 runs in on a sloping beach, the lower water particles can no longer- 

 turn in circles, and vvill have to move in straight lines along the 

 bottom. The highar vvater particles will turn in ellipses, which 

 approach closer and closer to circles the higter up they are. When 

 the horizontal movement extends nearly to the surface, the wave has 

 changed from, a deep-water wave to s ground-water wave , Tte change 

 between these waves is in general very uniform. 



It is the depth of the water alone which determines the speed of 

 the ground-water wave , i .e . 



V = Vid~ 



wtere d is the depth of the water, and g is the acceleration due to 

 gravity. 



As the ground-water wave involves water motion clear doT.vn to 

 the bottom, it is ob'/icus that the wave movement must influence the 

 latter. The wave is retarded by the bottom, and in doing so it uses 

 some of its energy to move loose bottom material if this is to be 

 found. Ithen the wave is greatly retarded, the crest of the wave falls 

 forward, this is called breakers (surf). Tte location of the breakers 

 is dependent upon the depth of the water, the elevation of the bottom 

 and also on the height of the wave and the strength of the 'svind. As 

 a result the distance of the breaker from the coast is not only 

 different on different coasts, but on the one and same coast it m.oves 

 in accordance to the immiediate conditions o One can say that it is a 

 fact that the breakers occur where the depth of the water is lo5 ~ 2 

 times the height of the wave. 



The energy of the ground-water wave can be expressed ass 



E = h^ L 



¥hen the wave breaks for the first time, all its energy has not 

 y3t been exhausted. A. smaller wave continues towards tte coast line 

 until tte water is not deep enough to permit this wave to exist. 

 Then the wave breaks againj this process can go on several times before 

 the v^ave finally dissipates all of its energy. As all the energy is 



