A Treatise On The Principles And Practice Of Harbour Engineering

30 HARBOUR ENGINEERING within the basin. For both purposes the design adopted may be considered as the most suitable. The movement of the sand along the coast is of a two- fold character. In shallow water the sand is carried by the waves along the shore and accumulâtes at each exposed point, which tends to prevent its further movement. For that reason the more the southern mole of the com- mercial port was extended into the sea, the more rapid was the growth of the coast in the angle between the mole and the shore; but, in the future, this growth will be slower, first, because the depth of the sea increases further from the shore, and secondly, because the mole was built out at once to a considérable distance and to a great depth, which obliged the waves from the west and south-west to glide along the mole and dash against the coast, thus scattering the sand collected. Certainly this does not prevent the harbour from silting up, but the sand is carried for a long distance along the coast, and therefore the danger of accumulations at the entrance of the harbour is considerably diminished. Beyond the breakwater the movement of the sand is produced by the coast current, in which the particles of sand are suspended. If the currents do not meet with any obstacles, the greater part of the sand is carried along the coast and is left in sheltered places, and this action is favoured by the circumstance that the breakwater and the point of the southern mole form a straight line. As regards the ice, which generally moves backwards and forwards from north to south, the arrangement of the walls in one line is very convenient. There is nothing to stop the ice and give isolated masses time to freeze together under the influence of the cold coast winds. Consequently there can be no accumulation of large ice masses, and a strong ice-breaker can at all times easily make a way out of the port into the open sea. The ice in the harbour, broken up by the ice-breaker passes witliout difficulty through the three outlets; but this ice, owing to the mildness of the climate, is never so thick as to be a serions obstacle to the movement of the ships.” The military port, as formed, is 7,700 feet long, 7,000 feet wide, and occupies about 1,200 acres. Its natural depth is 14 feet at a distance of 1,400 feet from the coast, 22 feet at a distance of 3,500 feet, and it gradually increases to 29 and 30 feet as it nears the breakwater. The width of each of the three entrances is 700 feet, and the general depth seaward is 30 feet, though diminished in places to as little as 24 feet. Madras Harbour.—The oase of Madras Harbour is a striking instance, amongst many which might be cited, of the difficulties attending the effective realisation of benefits theoretically deducible from principles which are ap parently sound in themselves and from a design conforming thereto so far as the available data will permit. Much that was hoped for has not corne to fruition, and justifiable expectations have been disappointed. The commercial ports of India are not numerous, in spite of the enormous extent of its seaboard. They can almost be counted upon the fingers of one hand, and most of them are of comparatively recent development. Up to the year 1875, there was nothing at Madras of the nature of a harbour, either