CONSIDERATIONS AFFECTING DESIGN OF HARBOURS. 147 



Soundings should be taken at sufficiently short intervals to 

 admit of contours being accurately laid down. These should be 

 plotted with special care over rocky ground. The nature of the sea- 

 bed should be ascertained by procuring a sample of the bottom at 

 each sounding, and, when the probable site of the works has been 

 tentatively decided upon, borings may, if necessary, be taken in order 

 to obtain more reliable information than the surface samples afford. 



Careful observations should also be made on the tides ; currents ; 

 height and direction of the heaviest waves ; description, extent, and 

 direction of littoral drift ; direction and force of prevalent winds ; 

 fetchj and so forth. 



(b) A careful examination of the district, with the view of 

 ascertaining what stone, sand, gravel, and other materials not 

 forgetting water are available for the works. 



(c) A consideration of possible sites for work-yard and 

 quarry, and of the approaches or means of access thereto ; also 

 of the means of transporting stone and other materials to the 

 works/and possibly, in some cases, of landing not only materials, 

 but also heavy " plant." 



(d) A careful consideration of the general facilities which 

 the locality affords for the construction of the work contemplated, 

 including the important question of " labour." 



It is scarcely needful to say that, in planning a harbour, the 

 number, size, draught, and description of vessels likely to use it 

 must be kept in view ; and also the special kind of trade which 

 may be carried on. 



The provision of good beaching-ground and spending-beaches, 

 and of ample quay space, easily accessible by road and rail, are 

 important points to remember, especially in connection with the 

 smaller classes of harbours. 



The site to be sheltered should, if possible, provide not only 

 for the immediate wants of the port, but also for increase of 

 trade; and the works should, as far as possible having due 

 regard to present efficiency be laid out with a view to their 

 future extension. 



The position and direction of the harbour entrance or 

 entrances should receive careful attention (Chap. IX.). 



In designing harbours especially large ones the degree of 

 shelter which it is necessary to afford should be carefully con- 

 sidered, because the cost of a work may be greatly affected by 

 it. Thus a breakwater intended only to break the waves, but 



