The New International Encyclopædia/Harbor
HARBOR (ME. harbor, herbore, herberwe, herberge, Icel. herbergi, OHG. heriberge, Ger. Herberge, from OHG. heri, Ger. Heer, AS. here, army + OHG., Ger. bergen, AS. beorgan, to shelter). An indentation or inlet on the shore of a sea or lake so protected from the winds and waves, whether by natural conformation of the land or by artificial works, as to form a secure roadstead for ships. In the broadest meaning harbor works include all the structures and appurtenances which facilitate the safe anchorage, loading, unloading, and repairs of vessels which seek harbors in the way of commerce and safety from storm; in this sense quays, docks, breakwaters, jetties, piers, and wharves, etc., are essential parts of harbors. In this article, however, the broad question of harbor construction as illustrated by typical harbors will alone be considered. For specific consideration of the parts of harbor works, see Breakwaters; Docks; Jetty; Lighthouses; Quays; etc.
Early Harbor Works. With the birth of commerce and naval warfare, in the earliest ages of civilization, arose the necessity for artificial harbors. The Phoenicians set to work to protect their scanty strip of Levantine coast. At Tyre, two harbor's were formed, to the north and to the south of the peninsula on which the city was placed. At Sidon, similar but less extensive works long testified to the wealth and engineering genius of the Phœnicians. The breakwaters were principally constructed of loose rubble. Carthage, in another part of the Mediterranean, also possessed a harbor, though its site is not very satisfactorily determined. It was in two divisions, formed by moles; time, however, has dealt so hardly with it that few traces remain. In Greece nature provided so many navigable inlets that little remained to be done by man. Nevertheless, some minor works were executed at the Piræus and elsewhere, chiefly for warlike purposes. The Romans, finding ships necessary to the dominion of the world, set about constructing harbors for them. The coasts of Italy still show how well they understood both the principles and the practice of this branch of engineering. A distinguishing feature of their harbor-making is the open or arched mole. Built with open arches, resting upon stone piers, it gives full play to the tidal and littoral currents, thus preventing the deposit of sand or mud; but in proportion as this advantage is increased (by increasing the span of the arches), so also is the agitation, and consequent insecurity, of the water within.
The decay of commerce and civilization, consequent upon the fall of the Roman Empire, put a stop to harbor-making; nor did the art revive until the revival of commerce by the Italian republics of the Middle Ages. The rich traffic of Venice and Genoa soon led to the construction of suitable ports at those places; and the moles of the latter city, and the works in the lagoons of Venice, remain to this day. France was next in the field, embanking, protecting, and deepening the mouths of the rivers along her northwestern shores, as at Havre, Dieppe, Dunkirk, etc. In 1627, during the siege of La Rochelle, Metezeau constructed jetties of loose rubble-stone, to prevent access to the city. England lagged far behind her Continental rivals. With few exceptions, her ports were absolutely unprotected, or rather uncreated, until late in the last century. Two of the few exceptions were Hartlepool, where a harbor was formed about 1250, and Arbroath, in 1394. In the seventeenth century, at Whitby and Scarborough, also in Yorkshire, rough piers were thrown out, protecting the mouth of the port; while at Yarmouth, in Elizabeth's reign, a north jetty, and subsequently a south one, were formed. An ancient mole existed at Lyme Regis. But the chief efforts of the early English engineers were directed against the shoals and waves of Dover. With the advent of Smeaton, however, things took a different turn; and now few countries surpass Great Britain in the number of artificially improved commercial harbors, or in the just appreciation of their importance.
The development of harbor works in America, of course, belongs entirely to modern times. The first regular appropriation for harbor work in the United States was made in 1802; it amounted to $30,000, and was to he devoted to the erection of public piers at Philadelphia, Pa. In 1822 an appropriation of $22,700 was made for the construction of a harbor of refuge in Delaware Bay. The first approach to a river and harbor bill was made in 1826, when about $150,000 was appropriated for carrying on work in about twenty localities. From 1826 to 1838 aggregate appropriations carried by the various river and harbor bills were about $9,000,000. From 1838 to 1866 the aggregate expenditure was $6,600,000. The total aggregate expenditure of the United States on river and harbor works from 1820 to 1894 was $262,845,900. Since 1894 the annual amount set aside by Congress for such works has rapidly increased, until in 1900-01 the River and Harbor Bill called for an appropriation of nearly $60,000,000 for new work, and the Sundry Civil Service Bill called for an appropriation of $7,000,000 for continuing work in progress.
Harbor Construction. The designing and construction of harbors constitute one of the most difficult departments of civil engineering. In discussing this branch of the subject attention will be limited to commercial harbors, including harbors of refuge. The general plan of commercial harbors differs in different nations, and there is a great diversity of form due to the methods of commercial means of disposing of the freight received from vessels. It may be set down, as a general rule, that the ship itself does not determine the character of the harbor beyond the fact that it must be of sufficient depth to accommodate ships of the maximum draught using the harbor. In some of the most important ports of the world there are practically no installations for handling freight, the ships anchoring in the open harbor and discharging their cargoes into lighters. Railways play a far more important rôle in determining the arrangement of the harbor, particularly in regard to the dock and quay arrangement. In the last respect, also, the local movement of commerce of the city itself plays an important part.
Turning now to the natural conditions which influence the character and arrangements of harbors, it may be stated that the topographic and geologic conditions exercise a decisive influence. A harbor may be situated directly upon the seacoast or in some river, bay, or gulf, or far in the interior on some river or maritime canal. The effects of the ocean, the action of the winds and tides, and the general conformation of the shore-lines are other controlling factors in determining the arrangement of harbor works. Finally, the nature of the soil, whether alluvial, or diluvial, or rocky, plays an important part in the arrangement of the basins, either natural or artificial, and the adoption of quays, jetties, piers, etc.
The great variety of commercial and natural conditions which influence the arrangement of harbor works of course call for a corresponding variety of arrangements; it is obviously impossible to describe each here. For the sake of clearness we may somewhat arbitrarily divide harbors into, first, those located on a comparatively open coast; second, those located at river mouths or on bays or gulfs, and thus more or less landlocked; and third, those located well inland on rivers or maritime canals.
The simplest form of open-coast harbor consists of a quay wall or bulkhead wall open to the sea, and serving only to enable ships to tie up alongside the shore and discharge and receive cargoes. Such a quay affords comparatively no protection from the winds, tides, and currents. The next advance is a straight pier extending out from the shore. This pier affords little shelter to ships from waves coming directly inshore, but in case of winds and waves along shore it affords 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.
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.
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.
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 descriptions of important recent harbor works will be found scattered through the proceedings of the various engineering societies and the engineering papers.