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TAMH: Source Material
Libau: Construction of military harbour 1887
The Military Harbour at Libau
Brysson Cunnigham, Harbour Engineering
Griffin & Company, London 1908
From Jarintzoff, The Military Outport of Libau,Min. Proc. Inst. C.E.126
'In designing the general arrangement of the sheltering constructions of the outport, two questions had to be taken into consideration: (1) to lessen as much as possible the risk of the entrances and of the interior of the port being silted up by the coast drifts; (2) to prevent floating ice from accumulating in front of the walls and to assist the escape of the ice formed 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 accumulates at each exposed point, which tends to prevents its further movement. For that reason the more the southern mole of the commercial port was extended in to 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 moel was built out at once to a considerable 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 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 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 string 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 without difficulty through the three outlets; but this ice, owing to the mildness of the climate, is never so thick as to be a serious 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.
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