protection on its lee side. Another step in advance is to build the pier bent or curved with its concave side toward the shore. A still further improvement is to build two curved piers converging toward each other so as to include a harbor basin with an opening between the sea ends of the piers. Still another method is to build off shore an insular breakwater, which prevents the waves from breaking on the shore, and thus forms a comparatively tranquil basin between the breakwater and the shore. Harbors of all these forms are found in practice. More generally, however, two or more of the structures mentioned are combined to form harbor basins of various forms and dimensions. Figures 1 and 2 show in outline form two representative open-coast harbors.
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Fig. 1. |
Fig. 2. |
When the conformation of the coast-line is of the nature of an indentation in the land, as in the case of a bay, gulf, or river-mouth, then a portion of it may be utilized, to take the place of one or more of the structures necessary to form an open-coast harbor. For example, the harbor of New York is so inclosed by land that no artificial structures in the shape of piers or breakwaters are needed to secure a tranquil harbor basin. Where the bay or inlet is less perfectly landlocked, piers, breakwaters, or jetties are constructed to supply the necessary protection at the exposed points. Figs. 3 to 6 show actual arrangements of such structures in different circumstances.
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Fig. 3. |
Fig. 4. | |
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Fig. 5. |
Fig. 6. |
The artificial works involved in inland harbors consist of jetties at the mouth of the river or canal, bank protection, and other constructions for preserving the channel, and the building of docks and quays in the harbor proper. Among the notable inland harbors of the world are those of Hamburg, Manchester, and Amsterdam, in Europe; and Charleston and Philadelphia, in America. Fig. 7 shows the entrance harbor of the ship canal leading to the harbor of Amsterdam, and Fig. 8 that at the entrance of the Suez Canal, at Port Saïd.
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Fig. 7. |
Fig. 8. |
In what has preceded, we have concerned ourselves only with the general arrangement of harbor structures under different topographic conditions. For specific information concerning jetties, breakwaters, docks, piers, quays, etc., the reader should consult the articles with these titles. Whatever the construction and arrangement of these constituent structures of a harbor may be, they are such that the harbor consists of an entrance, of an anchorage space, and of docks. By the entrance is meant the navigable pass by which vessels enter the harbor. Some ports have natural entrance channels of large dimensions and great depth, and in other harbors this channel is of small size and has to be artificially constructed and maintained. Generally speaking, the minimum width of practical entrance for ships of modern dimensions is from 230 feet to 490 feet, but for large commercial ports it should be preferably from 650 feet to 1000 feet wide. Sometimes the entrance channels constitute the anchorage space tributary to the entrance channel and the docks. No general rule can be laid down for the area of anchorage space, for this is governed by the local conditions at each port. When the natural harbor bank does not give sufficient room for the commerce of a harbor, various methods are adopted for increasing this shore space. The most simple is to build out from the shore a series of piers or wharves with water spaces between them to form docks. When this is not practicable quays are built which inclose dock basins. The nature of these two classes of structure is described in the article on Docks.
For a comprehensive treatise on harbors, consult: De Cordemoy, Les ports modernes (Paris, 1900); Vernon-Harcourt, Harbors and Docks (London, 1885). The best
