encroaches in the entrance to the harbor, dredging will -usually be 

 required for navigation purposes and this will prevent the sand from 

 being moved across the harbor to the other side.. The wave which 

 passes the deep water at the head of the .ietty, and moves in the 

 direction of the material moving power, will thus be without material 

 when it reaches shoal water. Here the wave will pick up a quantity 

 of sand proportional to the energy of the wave, and the coast will be 

 eroded to a point A, (see Figure IS) which is determined by drawing 

 the line S-A parallel to the direction of the material-moving power » 

 Usually one cannot protect successfully the coast over the distance 

 K to A^ partly because groins cannot prevent the beach beyond their 

 ends from being eroded, and partly because hardly any material is 

 deposited. However, a revetment founded deep into the bottom will 

 somietijnes be suitableo 



If one wants to avoid the shoaling of entrances to harbors 

 one can build the harbors as island harbors, i.e. harbors that are 

 connected to the mainland by a bridge. The first harbors of this 

 kind (Amager and Snogebaek, both on Bomholm.) were constructed about 

 50 years ago and have been successful. The island harbors on Bornh- 

 olm consist of a small basin as illustrated by the harbor of Amager 

 (Figure 19) » The harbor of Handested, which was first built as an 

 island harbor became too big in proportion to its distance from the 

 coast with the result that sand was deposited and today it is con- 

 nected with the mainland. 



The proposed fomiula for material -moving power is in agreement 

 with the conditions observed over the entire Danish coast. Further- 

 morej, the formula has also been tested on the coasts of the Bassian 

 Arctic Ocean and on the coasts of the Caspic Sea„ The formula has 

 furthermore shown good agreement on all coasts of the Baltic Seao 

 The formula is being taught at technical colleges in Russia and 

 Germany, 



Mro Paulis Revelis, top engineer of the Latvian water building 

 department in Riga^ has written a thesis concerning the material- 

 drift along the coasts of Latvia, and he has used Mr, Munch-Petersen's 

 formula. The total coast line of Latvia is about 300 miles (500 

 kilometers), and about 270 kilometers of this is coast open to the 

 Baltic, The remainder is open to the Bay of Riga, (The west coast 

 of Jutland from Grenen to the border is about 400 kilometers „) The 

 Latvian coast consists of soft material^ sand, gravel and small stones 

 with a clay-underlay. As there are several large harbors on the 

 coast one will understand that the question of material-drift is of a 

 great interest. Figure 20 shows the Latvian coast from Lithuania 

 on the south to Esthonia on the north. The coast open to the Baltic 

 is in the north and terminated by a rather sharp point, Kolkasrags, 

 outside which there is to be found a sandbank more than 6 kilometers 

 long_, on the tip of which a lighthouse has been built. The conditions 

 remind one of Skagen, The direction of the material-moving power is 

 northwards with the exception of a short reach near Pape, In the 

 Bay of Riga the miaterial drift is to the south on the west side, but 

 a little beyond Riga it turns northo 



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