BREAKWATER AT VENICE.
CHAPTER XIII.
The Breakwater.
Breakwaters, Ancient and Modern—Origin and History of that at Cherbourg—Stones Sunk in Wooden Cones—Partial Failure of the Plan—Millions of Tons dropped to the Bottom—The Breakwater Temporarily Abandoned—Completed by Napoleon III.—A Port Bristling with Guns—Rennie’s Plymouth Breakwater—Ingenious Mode of Depositing the Stones—Lessons of the Sea—The Waves the Best Workmen—Completion of the Work—Grand Double Breakwater at Portland—The English Cherbourg—A Magnificent Piece of Engineering—Utilisation of Otherwise Worthless Stone—900 Convicts at Work—The Great Fortifications—The Verne—Gibraltar at Home—A Gigantic Fosse—Portland almost Impregnable—Breakwaters Elsewhere.
A breakwater, we are told on the highest authority, is an obstruction of wood, stone, or other material, as a boom or raft of wood, sunken vessels, &c., placed before the entrance of a port or harbour, or any projection from the land into the sea, as a mole, pier, or jetty, so situated as to break the force of the waves and prevent damage to shipping lying at anchor within them. Thus the piers of the ancient Piræus and of Rhodes; the moles of Venice, Naples, Genoa, and Castellamare; the piers of Ramsgate, Margate, Folkestone, Howth, and the famous wooden dike thrown across the port of Rochelle. The term, of late years, has been almost exclusively applied to insulated dikes of stone. Of this description of dike for creating an artificial harbour on a grand scale, Cherbourg, Plymouth, and Portland present leading examples. The former, already mentioned in this work, claims our attention.
The French, happily our good friends to-day, were not always so, and there was a period when the splendid natural harbours, bays, and roadsteads of this country were a source of annoyance to them. While nature had been more than kind to us, their coast presented a series of sandy shores, intermingled with iron-bound coasts, bristling with rocks. De Vauban, the great engineer, was employed by Louis, the Grand Monarque, to inspect the Channel shores of France, and his natural sagacity and great knowledge [pg 189]caused him at once to select Cherbourg as one of the best points for forming an artificial harbour, protected by suitable fortifications. Other engineers recommended the same port, and one, M. de la Bretonnière, proposed that a number of old ships should be loaded with stones and sunk, while a large quantity of stone should be also thrown around them to form a grand breakwater, which should rise fifty feet from the bottom. This idea was abandoned, as it appears, partly from the fact that France had not old vessels enough to spare for the purpose, and that it would cost too much to purchase them from foreign nations.
In 1781 an eminent French engineer proposed that, instead of one continuous breakwater, a number of large masses or congregations of stones, separated from each other on the surfaces but touching at the bases, should be built on the sea bottom, believing that they would break the force of the waves almost equally well. As a part of his plan he suggested that they should be sunk in large conical caissons of wood, 150 feet in diameter at the base and sixty feet broad at the top. These wooden cones were practically to bind and keep the stones together. They were to be floated to the site with a number of empty casks attached as floats, then detached, filled with stones, and sunk. An experiment at Havre having been considered satisfactory, the Government accepted the idea, and ordered that operations should be immediately commenced at Cherbourg. A permanent council was appointed, as were officers and engineers. In 1783 barracks and a navy-yard were built, and at Becquet, a short distance from Cherbourg, an artificial harbour, capable of holding eighty small vessels for the transport of the stone, was literally dug out.
On June 6th, 1784, the first cone was floated to its destination, and a month later a second was similarly conveyed, in the presence of 10,000 spectators. Before the latter could be filled with stones a storm, which lasted five days, half demolished it. In the course of the summer and autumn not less than 65,000 tons of stone were deposited in and around the cones. In 1785 several more cones were completed and sunk; at the end of the year the quantity of stone deposited amounted to a quarter of a million tons, and at the end of 1787 a million tons. At the end of 1790, when the works had been seven years in progress and the Government was getting very tired of the whole matter, between five and six million tons of stone had been dropped into the sea. M. de Cessart, the engineer, found that, in order to sink five cones per annum, he had to employ 250 carpenters, 30 blacksmiths, 200 stone-hewers, and 200 masons.