309 



BREAD, BEES, AND ALE, ASSIZE OF. 



BREAKWATER. 



310 



ciously managed, or one nearly similar to it, should not be adopted in 

 the metropolis. 



BREAD, BEES, AND ALE, ASSIZE OF. [ ASSIZE.] 



BREAKWATER, a construction formed in the sea, or in any large 

 body of water, for the purpose of destroying the action of the waves, 

 and of thus securing the tranquillity of a roadstead. A breakwater, in 

 fact, as the word has been of late years applied, differs from a pier or a 

 jetty, insomuch as it serves to protect a roadstead, and is formed in 

 deep water, without any connexion with the shore ; whereas piers or 

 jetties only shelter closed basins, and are joined to the main land. 



The engineers of antiquity executed, during the prosperous days of 

 the Roman empire, some remarkable works of the nature of break- 

 waters, as we understand the term ; and the entrances to the ports of 

 Ostia and of Antium were protected by artificial islands, formed so as 

 to break the force of the waves driving against them. It was not how- 

 ever until the latter end of the 18th century that modern engineers 

 undertook any great work of this description. At that period the 

 French government commenced the execution of the breakwater at 

 Cherbourg ; and subsequently similar operations have been carried on 

 at Plymouth, Cette, the mouth of the Delaware, in Lake Erie at 

 Buffalo, and at Portland, Dorsetshire. As the construction of the 

 breakwater at Cherbourg was attended with the greatest difficulties, 

 and has been studied more carefully than any of the analogous works, 

 it will be noticed a little more in detail. 



The breakwater of Cherbourg consists, at the present day, of a mass 

 of rubble stone, cast into the water and allowed to assume its own 

 natural outline ; it is 12,356 English feet long, and in plan it presents 

 the form of a species of chevron, whose arms are of unequal length, 

 and which presents towards the open sea an obtuse angle at the 

 summit, of 169. The depth of water in this part of the roads is 

 61 feet at low water of average spring tides, and the width of the base 

 is about 298 English feet; its transverse section may be described 

 generally as follows : From the base to the level of about 22 feet below 

 high-water line of spring tides, the slope on the land side is in the 

 ratio of 1 in base to 1 in height (1 to 1) ; the top of the mass has then 

 a much more gentle inclination, for in a width of 19J feet its inner 

 summit attains the height of 15] feet below the said high-water line, 

 or the slope is in fact, nearly 3 to 1. At this level the slope stops 

 against a wall, almost vertical, which rises to 7 feet above the high- 

 water, or datum line, and is crowned by a platform of about 21 feet 

 in width, beyond which there is a solid granite parapet 8 feet wide and 

 5 feet high towards the sea. The outer line of this parapet is itself in 

 continuation with the sea face of the wall, forming in fact the crown 

 of the breakwater ; and the wall is built of course granite ashlar, laid 

 with the greatest care, and composed of the best materials, upon a 

 general bed of hydraulic concrete 5 feet thick, extending over the 

 loose rubble walling, at a level of 29 feet below datum. Beyond the 

 edge of the masonry which protects the foot of the vertical wall, the 

 slope assumed by the loose rubble, towards the open sea, is 1 in 10, 

 until it reaches the depth of about 47 feet below datum ; and from 

 that level to the base the sea slope is about in the ratio of 1J to 1. 

 It waa found that the small stones at the foot of the vertical wall were 

 very much disturbed by the movement of the waves ; but this incon- 

 venience has been of late materially obviated by covering the fore 

 slope of the breakwater with huge artificial blocks of rubble masonry, 

 set in Portland cement. The area sheltered by this gigantic structure 

 is not less than 1926 acres nearly; but only about one-third of this 

 area has a depth of 26 feet at low water of spring tides. At the 

 bottom of the roads thus artificially protected are the military and the 

 commercial port* of Cherbourg. 



I U ! 'J 



fig. 1. Cherbourg. 



The works for the construction of the Cherbourg breakwater were 

 commenced about 1783, by De Cessart, under the government of 

 Louis XVI. ; and they have been carried on with various success and 

 ii|*>n various plans, by all the governments of France, until in the year 

 1853 the whole of the substructure was completed to such an extent 

 as 'to allow the commencement of the fortifications proposed to be 

 erected. It is estimated that the total cost up to 1853 was not less 

 than 2,682,4911. sterling. 



Plymouth breakwater is formed in a bay which is naturally more 

 sheltered than the comparatively speaking open roadstead of Cherbourg ; 

 and ita construction was favoured by the existence of some natural 

 reefs upon the direction proposed to be adopted : nevertheless there 

 was great boldness in it* design, and the rapidity of its execution 

 contrasts markedly with the slow progress of its great prototype. The 

 plan of the Plymouth breakwater consists of a principal rectilineal 

 with two return arms, forming with the centre body obtuse 



angles towards the sea of about 135 ; the length of the centre body 

 is about 1000 yards, and that of each of the arms about 350 yards ; or 

 in other words, the length of this work is only 5100 feet, whilst that 

 of the Cherbourg breakwater is 12,356 feet. A surface of about 1120 

 acres is protected by the work executed at Plymouth. 



Fig. 2. Plymouth. 



Originally it was intended to make the top of the breakwater only 

 11 yards wide, and the bottom 55 yards wide ; but during the execu- 

 tion of the work, those dimensions were respectively increased to 

 15 yards and 133 yards. At the level of low water of spring tides, a 

 set-off of about 22 yards in width is formed ; and the sea slope from 

 this point upwards is paved with very large stones, bedded in Roman 

 cement ; and the paving has been continued below low water line by 

 means of the diving-bell. The height of the crown of the Plymouth 

 breakwater is only 2 feet above the level of the high spring tides ; 

 whilst the height of the parapet of the vertical wall of the digue at 

 Cherbourg is at least 12 feet above this line. The questions connected 

 with the outlines of the respective works in the zones exposed to the 

 action of storms will be noticed hereafter. 



The Delaware and the Cette breakwaters do not exemplify any par- 

 ticular principle, nor do they illustrate any peculiar mode of construc- 

 tion, so that it may suffice to say that the former is about 1000 yards 

 long, measuring upon the line of high water. Its slope towards the 

 harbour is about 1 to 1 ; and the top, which finishes at about 5 feet 

 4 inches above the level of the highest spring tides, is about 30 feet 

 wide. The outer slope is carried down, with an inclination of 3 base 

 to 1 height, to a depth of about 19 feet below low water of spring tides, 



Fig. 3. Delaware. 



Fig. 4. Cette. 



and, from thence to the bottom, the inclination is only as 1 to 1. The 

 breakwater at Cette is principally remarkable on account of the great 

 height to which the mass of masonry is carried above the high-water 

 line ; this is not less than 19 feet ; and perhaps also the cubical con- 

 tents of the transverse section may be cited as being worthy of remark. 

 The total depth of water is only 24 feet in this part of the Mediter- 

 ranean, but the width of the foot of the Cette breakwater is not less 

 than 254 feet; its total length is about 514 yards, and the outline on 

 plan is convex towards the open sea. The breakwater at Buffalo, in 

 the state of New York and in Lake Erie, is constructed with nearly 

 as much solidity as analagous structures in the ocean. It is, however, 



Fig. 5. Buffalo. 



made with a vertical face towards the shore, and at about 5 feet above 

 the water-line there is a platform 18 feet wide; upon this a wall is 

 erected 5 feet high and 15 feet wide, from the outer edge of which the 

 rubble masonry is carried with a slope of 3 to 1 to the shore of the 

 lake. 



The Portland breakwater is being constructed upon precisely the 

 same principles as that of Plymouth ; and it is therefore only remark- 

 able on account of the mechanical contrivances adopted in the course 

 of its execution. 



There have been submitted to the public, of late years, a great 

 number of schemes for forming floating breakwaters, wave screens, or 

 for employing some more economical system than that of creating, as 

 it were, artificial islands. But the marked failures of these ingenious 

 contrivances have been so notorious, that it would be unnecessary here 

 to discuss any of them. The attention of engineers charged with the 

 execution of such works is, in fact, now exclusively directed to the 



