A Treatise On The Principles And Practice Of Harbour Engineering

HARBOUR DESIGN 19 generally. In regard to all thèse, certain localities will be more favourably situated than others. But, except in rare instances, the engineer can hardly expect to have the opportunity of allocating a harbour and of designing it in toto. Trade routes are sufficiently firmly established to preclude the diversion of much traffic to other lines. Au occasional harbour of refuge, with a fishery station or so, marks the limits of entirely new construction at the present day. Yet, at the same time, there is great and increasing scope for the develop- ment of maritime works already in existence, and the enlargement and improvement of harbours forms one of the most important fields of civil engineering. Procedure in Desig’n.—Such being the case, the unrestricted choice of a site will rarely lie within the province of the engineer. The locality, at anyrate, will already have been determined and the preliminary dispositions established, before his services are requisitioned. It falls to his lot, therefore, to utilise existing conditions and to devise a modus vivendi out of circum- stances beyond his control. Assuming, momentarily, for the purpose of discussing the question in all its bearings, that the site is a virgin one, there are certain preliminaries to be carried out before any scheme can be laid down. We will deal with them in their natural order of procedure. Thus, the first point would be to make a survey of the neighbourhood, and to prépare a chart indicating the depths of water in the vicinity. Not only should a complété set of soundings be taken, but borings should also be made to ascer- tain the nature of the ground, its fitness for anchorage, and the extent to which it lends itself to an economical inerease of depth, should this be or become neces- sary. The depths obviously must be sufficient to meet the require- ments of the deepest draughted vessels which are likely to fre- quent the place,1 and it should not be overlooked that some allowance is necessary for the pitch or surge of a vessel in rough water, whereby its keel descends below the normal level. Natural Phenomena. — After the preparation of the sur- Fig. 10.—Wind Diagram. Frequency ordinates set off from centre; intensity ordinates from frequency curve. vey and the plotting of the contour lines (or lines of uniform level, as shown in fig. 2), the engineer will search local records for data, and also make 1 See footnote, p. 14.