oblique direction up on the shore. On the shore part of the material 

 is caught in tte wave backwash. Then it is caught by the conveyor 

 belt and moved along the coast until a new wave comes along^, etc. 

 Erosion or accretion is solely dependent upon the difference in quantity 

 of material that is deposited and that is carried away. If there is no 

 soft material wtere the waves come from, they will, when they reach 

 soft rraterial, absorb a lot and material will be carried away. 



It follows that one cannot determine the volume of material drift 

 from the material found on the shores. On a coast that has nc loose 

 materials T,tiatsoever, tlie material drift can very well be considerable. 

 This one can see (unfortunately often, too late) when the movement 

 of the material has been blocked by a harbor jetty. This action vrill 

 result in sand deposits on coasts that are nearly free from sand. 



IThen the wind blows in an oblique direction toward the coast, 

 the material will be moved along the coast in the direction the wind 

 blows. Close to the shore the waves "vv'ill be turned to approach the 

 shore at more or less a 90 degree angle to the depth cu?."-ve3. However j, 

 this cannot be done without the bottom or the bcttom paterial being 

 influenced, and moreover the waves will usually approach the shore 

 sonewhat obliquely. It is obvious that the closer the wave approach 

 is to perpendicular the more energy there -will be for disturbing 

 coast material. On the other hand, the ability of the waves to trans- 

 port material along the coast will increase, as the obliquity of the. 

 wave to the belt in which the material drift increases. Exr.eriencs 

 shows that material raovenent increases when the angle between the 

 direction of the wave and the coast decreases, and that it is close 

 to its maximum when this angle is zero, i=e, v^rhen the original wave 

 (the deep-water wave) moves parallel to the shore. As the wave enters 

 the belt in i^ich the material drifts, it will very soon be forced 

 to turn so much that arosion of the bottom material will occur, and 

 this action will be followed by transport of the material. 



The dependence of material drift on tte direction of the wind can 

 be illustrated as suggested in Figure 3, which approximates a cosine 

 curve with the exception that winds in the second quadrant are added 

 because land winds vjhich blovf nearly in the direction of the ooast 

 influence the material drift. However, the question of the dependenc-o 

 of the material drift upon the direction of the wind is not yet clesi". 

 Several investigators are of the opinion that a maximum, drift occurs 

 when the wave approaches at an angle of 4-5 degrees, this condition 

 corresponds to a cosine-sine curve and not to the cosine cyi""?; shorn. 



Let us noTif consider what Mr. Munch-Petsrsen calls "The Material 

 Moving Power*?. This is a notion which, one can say. has brought ohe 

 study of the problem of material drift a very long step forward^ and 

 it has consequently been the object of consideration by .several 

 foreign investigators. The problem is to establish a formula defin- 

 ing the transportation ability of the waves, (whether or not there 

 is material to be transported is another question) o If we consider 

 a straight, regular coast without appreciable headlands^, then we can^ 

 according to what has been said before, express the wave's ability 



