A Treatise On The Principles And Practice Of Harbour Engineering

CHAPTER III. SURVEYING, MARINE AND SUBMARINE. Soundings—Methods of Procedure—Appliances: Line, Chain, and Pole—Sutcliffe’s Apparatus—Maintenance of Alignment—Variations in Water Level- —Tide Gauges Current Observations—Floats—Localisation—Plotting Positions—Diving Operations Bells—Diving Dress and Equipment. Marine Surveying”, while generally and appropriately considered as constituting a special department of maritime work, with a field and purview of its own, has at the same time certain of its operations so closely associated with the ordinary routine of harbour engineering that some reference to them, if not absolutely imperative, becomes, at least, eminently désirable. It is not contemplated, however, to enter into any detailed explanation of the principles underlying the carrying out of a hydrographical survey, nor even to describe in outline the series of operations involved in the prépara- tion of a chart of any portion of the coast-line for purposes of harbour design. Such matters, affording scope for no little mathematical investiga- tion and requiring much elucidation of particular problems, are to be found treated in geodetic text-books specially devoted to that end; and even supposing that this were considered an appropriate course to pursue, it would hardly be possible to deal with the questions which would inevitably arise, in a manner at once sufficiently comprehensive and succinct for inclusion within the limits imposed by the requirements of this treatise. The operations more immediately concerning the engineer in the actual constructional and maintenance work of a harbour are, (a) the taking of soundings, and (6) the determination of the direction and velocity of tidal and fluvial currents. Our observations, therefore, will be confined to these points. Soundings.—The taking of soundings is a very common operation in navigation, but the appliances used in that connection and the methods in vogue are by no means identical with those characteristic of harbour practice. In the latter sphere much greater precision and accuracy are essential than can be afforded by the somewhat rough and ready appliances employed in connection with shipping. Manifestly the simplest way of taking a sounding, that is, of ascertaining the depth of water at any spot, is to lower a pole or weighted line until the bottom is rcached. If the pole or line be graduated to linear measure, the 43