A Treatise On The Principles And Practice Of Harbour Engineering

I6 HARBOUR ENGINEERING out into the sea is made to suffice, being provided with a level quay and covered sheds for the reception of merchandise ; but such cases are rare, and, generally speaking, it will be found necessary to provide an enolosure, practically complété, with an inner harbour, or docks, for commercial purposes. Indeed, in the case of a coast exposed to heavy seas, the adjunct becomes imperative. Estuarine Harbours find the requisite shelter already provided, in many cases, by rising ground flanking their entrances, and, indeed, many harbours situated in creeks and inlets are also admirably protected by adjacent hills so as to require no further defence. In addition to Cork and Queenstown, the harbours of Sydney, San Francisco, and Rio de Janeiro may be cited as cases in point. Instances of estuarine harbours are afforded by Liverpool, at the mouth of the Mersey; Dublin, at the mouth of the Liffey ; Havre, at the mouth of the Seine, and numerous other ports. The case of Liverpool is an admirable example, the form of the river at its mouth being excellently adapted for harbourage. The Mersey is broad and deep, expanding inwards from a narrow-necked entrance, while rising ground on both sides contributes the necessary shelter. But while estuarine harbours possess many advantages, they have corre- sponding defects. The majority of rivers are afflicted with bars, that is to say ridges of material lying across their entrances in such a manner as to reduce the available depth of water, and so impede navigation. The point is only mentioned here in passing : it is of such grave importance as to call for detailed treatment, and this must be reserved for a later chapter. River Ports, such as Bremen on the Weser, Hamburg on the Elbe, Glasgow on the Clyde, etc., and Canal Ports, such as Manchester, Bruges, etc., are comparatively free from many of the evils which affect harbours on the littoral, but they are attended by certain inconveniences of another kind. The navigation of inland waterways is a slow and tedious process for sea-going ships, and it involves considérable delay, which, in these days of rapid transit, counts for a great deal. Ports like Antwerp, Hamburg, and Rotterdam are very unfavourably situated for competing as regards expédi- tion and despatch with ports on the seacoast. True, there are advantages attaching to water carriage throughout, which outweigh the alternative of unshipment and transport by rail from the nearest seaport; but this faet does not invabdate the contention that the nearer the port to the great ocean highways, the speedier and better the distribution of freight. Moreover, river harbours are subject to the adverse influences of strong currents, freshets, and floods ; they have a continuous tendency to silt up, and they are even invaded at times by floating masses of weeds and mud. Under these particular circumstances, a river harbour should possess an entrance pointing downstream, making an acute angle with the bank, and the width of entrance should not be greater than is necessary for the manæuvring of the vessels which frequent the port.