BREAKWATERS.
The most important work and the most fun damental feature in connection with artificial sheltering or refuge harbors and roadsteads is the breakwater intended, as its name indicates, to break up and disperse heavy seas, thereby preventing the destruction of beaches and har bors and ensuring a haven for seacraft. They must be of great strength and stability.
When we realize that the force of the waves is beyond calculation, and that it is impossible to say what will be their size and pressure at a given time or location — it being known that those produced by great storms attain a height of 30 feet, with a pressure per square foot of from 6,000 to 7,000 pounds—we shall then comprehend the need of breakwaters, as like wise the difficulties in their construction. Some are constructed of timber, secured or anchored in sections, with openings permitting possibility of giving away. To avoid this dan ger, the modern engineer has endeavored to so construct that there will be no direct force. The best practice to-day involves making or finding a rock support for a mass of rubble, the water to go through, thus breaking the force of the wave. But the more usual con struction is to build the breakwater solidly of rubble, of concrete, of stone or of some com bination of these materials. The most feasible method is by the use of rubble, or irregular stone, which is sunk in the water and adjusts itself through the action of the waves. Con stant additions bring its mass to or above the surface, when its sloping sides are capped with solid masonry so adapted as to best resist the play of the waves.
so constituted that when one stone washes away another slips into its place. The face of the rubble .mound is inclined to the end of divert ing the waves to one side or cause them to spend their force upward. A concrete cover ing of the rubble mass may be formed by an choring metal piles through the rubble and throwing in concrete in bags.
While breakwaters generally run at a slight angle practically parallel to the shore, there is another type of the same known as training jetties that extend at right angles with the It has been found that the solid masonry constructed type of breakwater, of which the most notable example is to be found at Cher bourg, France, receives the force of the waves without diverting it, with the ever-constant shore. An excellent example of this latter is the series of jetties at Lido outlet channel. The length of the northeast jetty is 11,926 feet, while the southwest jetty is 10,551 feet in length. The distance between the outer paral lel sections is 2,970 feet. Thesejetties are very similar in construction to the Malamocco jetties at Venice, shown in Fig. 8. These last consist of two jetties, also, the northern one having a length of 6,962 feet, and the southern 3,137 feet. The distance between them is 1,545
feet. The bases are of rubble. The width at the top is 28 feet. The superstructure-6 feet 6 inches high and 13 feet 1 inch wide —is built up of masonry with an inner core of nibble. The Malamocco jetties cost ap proximately $1,600,000, and their yearly main tenance amounts to $3,200. The average veloc ity of the ebb current at ordinary tide through the channel is two feet per second.
In the waters of the United States are crib breakwater, 2,803 feet in length, with a light at its northerly end, the opening between this and the new breakwater forming a °South' harbor entrance, while the opening between the stone breakwater and the old breakwater is known as the °middle" harbor entrance. The longer extension of the new breakwater is of the rubble, stone-capped type, while the shorter i extension is of timber crib construction for the purpose of allowing vessels to moor alongside of it in the harbor. The new breakwater is located in the open waters of Lake Erie, paral lel with the shore, 1,500 feet from the pierhead line, and in 30 feet of water; its construction occupied six or seven years, at a cost of $2,200,000.
many breakwaters — certain of them evidencing the highest form of engineering skill. They are the result of modern commercial necessity that is being recognized more day by day. Perhaps the most important is that of Buffalo (Fig. 9)— a city whose natural harbor was comparatively insignificant — completed in 1903. With a geographical and waterway sit uation through which centred the great com merce between the East and the West, Buffalo was without adequate facilities for handling the freight and cargoes of the great trunk lines and the Great Lakes shipping, but through engi neering, by her great system of breakwaters, has overcome this disadvantage, and, as has been noted elsewhere in this chapter, stands tenth as regards tonnage handled among the world's ports.
Prior to 1903 there already existed two breakwaters at the port of Buffalo — one, the °north" breakwater, of concrete, 2,200 feet in length, with a light at its southerly end; and the other, or °old' breakwater, extending par allel, with a light at its northerly end opposite to the light mentioned on the north breakwater. The length of the old breakwater is 7,608 feet. Between the two lights is the harbor entrance. The new breakwater, or that of 1903, is lo cated south of the old breakwater, being of concrete construction for 7,261 feet, and con necting with a timber and concrete construc tion of 2,739 feet, having a light at its south erly end. Parallel and to the west is a timber In the following table are given additional dimensions and most typical modern break waters.