282 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



[Sept. 



This project was most insufTicient : it left exposed and withont defence 

 the most essential portion of the bay, that part best suited for the anchor- 

 age of large ships ; and the Tery circumscribed area which it was proposed 

 to proteet against the violence of the sea and the attacks of an enemy, 

 would have been accessible only to trading vessels, privateers, and other 

 small craft. 



In the year 1777, M. de la Bretonniere, capitaine de vaisseau, who was 

 thoroughly acquainted with the localities, had proposed to cover the road- 

 stead by a breakwater of sunken rocks. He republished in 179G a memoir 

 containing much valuable information in regard to the soundings, and other 

 matters of great interest in regard to the general advantages of Cherbourg 

 as a port of refuge for all classes of ships under all circumstances of wind 

 and weather. 



The project of constructing the breakwater in the direction of Point 

 Homet, was abandoned at the remonstrance of M. de la Bretonniere, and, 

 in 1780, it was resolved to adopt the direction which has since been given 

 to it, viz., from the point Querqueville to Felee Island. 



After a long delay as to the means to be adopted for enclosing the an- 

 chorage by advanced works, M. de Cessart recommended the ingenious 

 system of wooden caissons, in the form of truncated cones, 149 feet diame- 

 ter at the base; C5 feet diameter at the summit, and 05 feet of vertical 

 height. 



It was proposed to sink 90 of these cones in all, leaving a passage at the 

 east end of 27ti'J feet, and one at the west of 7674 feet. 



It was, in the first instance, intended to fill them entirely with loose 

 stones, but it was subsequently determined to fill them up with regular 

 masonry, above the level of the equinoctial low tides, and to connect the 

 cones with strong iron chains, thus forming a sort of open net work, which 

 should divide the action of the sea, and create smooth water in the road- 

 stead. 



The proposed construction, mode of launching, and immersion of these 

 cones, appeared to promise every success. One was built at Havre, and 

 floated in 1783. It was then taken to pieces, transported to Cherbourg, 

 and after some delay, caused by a gale of wind, was floated and sunk, on 

 the 6th of June 1784, at a distance of 3835 feet from Pel^e Island. 



A second was sunk tangent to the base of the first, in a westerly direc- 

 tion, on the 7th July following, but a gale coming on on the 18lh of August, 

 before this second cone was tilled with stones, it was carried away down 

 to low water mark. This event was the cause of, or the pretext for, great 

 changes in the dispositions which had in the first place been adopted. 



It was found that the stones, dispersed by the breaking of the second 

 cone, would entail the necessity of sinking a third at such a distance from 

 the first, that the interval would not be protected from the violence of the 

 sea. It was likewise considered, that, as the cones could be sunk only 

 during the spring tides, the completion of the work would require lb or 20 

 years' consecutive labour, and would cost 80,000,000 of francs. These 

 considerations led the Government to direct that the cones should in future 

 be only employed at intervals of 58 metres, 50 centimetres, and the inter- 

 mediate space filled in with large blocks of stone, and thus to form a break- 

 water, which was to be carried up to low water level. These intervals 

 were subsequently increased to 1230 feet; but after sinking 18 of these 

 cones at different intervals, thus isolated and imperfectly filled, they soon 

 experienced repeated damage, and this system of construction was accord- 

 ingly soon abandoned. All the cones which the sea had spared being 

 deemed useless, they were cut down to low water in the year 1789 ; one 

 alone was left entire, to indicate the limits of the passage, but in spite of 

 some care bestowed on its preservation, it fell to pieces on the 12tli of 

 February 1799. The successive destruction of all these cones, led to the 

 recognition of the system of breakwaters of sunken rock as the only pro- 

 cess calculated to ensure success. 



From this period the sinking of stones was carried on with such activity, 

 that by the end of the year 1790, the quantity of material sunk was com- 

 puted at 2,605,400 metres cube. Hitherto but vague notions had been en- 

 tertained of the depth of water, nature of the bottom, and of the force and 

 direction of the currents at dili'erent stages of the tide. These essential 

 considerations were neglected, and the establishment of the digue was re- 

 solved upon, at a distance of about 3,898 metres from the entrance of the 

 merchant vessels' harbour, in an easterly and westerly direction, forming 

 towards the centre a salient angle to the north of 169 degrees, which divides 

 the '■ digue" into two branches, of which the westerly one is 2,232 metres, 

 that on the east 1,530 metres in length, measured from the centres of the 

 two cones which had been sunk at the extremities. 



The angular disposition of the work thus determined, without regard to 

 the principles which prescribed a configuration quite the reverse, in order 

 to render it suscepiible of the greatest resistance, was dictated by the ne- 

 cessity of not obstructing the fire of Forts Koyal and Querqueville, destined 

 to defend the entrance to the roadstead. 



At this early stage, it would have been possible to modify the disposi- 

 tions in regard to these furls, of which the one was only planned, and the 

 other barely commenced ; but the War Uepartment insisted on carrying out 

 its own plan of defence, and the Marine Uepartment saw itself compelled 

 to renounce the advantages which would manifestly have accrued from 

 placing the breakwater more to the north, thus increasing the area of the 

 anchorage without any serious increase of expense, or augmentation of the 

 difliculties of construction. 



This first error was followed up by a second no less grave, and which 

 leaves no doubt that the soundings of the bay were then but very imper. 

 fectly known. The cone which was to form the eastern end of the digue 

 was sunk in 25 feet (8 metres 12 centimetres) water at low tide, hence the 

 water gradually shoals in the direction of Pel<;e Island, which is distant 

 about 975 metres. This passage was thus narrowed with the view of 

 obliging large ships to pass within good range of the fort on the island ; but 

 this purely military consideration led to the neglect of a most essential 

 maritime condition, for the depth of water in this passage is insufficient for 

 ships of the line at low water. It was likewise proposed, with the same 

 defensive view, to narrow the western entrance ; but after a careful exa- 

 mination of the depth of water, it was found necessary to establish the 

 western extremity of the digue at a distance of 2,339 metres from fort 

 Querqueville. But the passage of ships of the line thus established beyond 

 good range of the above fort, sensibly afl'ected the utility of this fortress ; 

 and had the naval and military projects been well concerted, it is not to be 

 concealed, that the defences would have been susceptible of a more advan- 

 tageous disposition, and that the greater part of the expense of the fort ia 

 question might have been saved. But all these inconveniences were dis- 

 covered too late. 



It was only in the month of July 1789 that orders were first given for 

 taking correct soundings of the bay, and for ascertaining with accuracy 

 the places accessible to vessels of all classes. 



In 1792 the Legislative Assembly, convinced of the extreme importance 

 of this great undertaking, procured a statement of the progress already 

 made at an expense of 31,000,000 of francs, including cost of establishment 

 and administration. Having fully recognised that the faults hitherto ob- 

 served in the execution of the works proceeded from want of concert and 

 combination in the different projects hitherto adopted, the Assembly ordered 

 the Executive Government to name Commissioners, chosen by the depart- 

 ments of War, Marine, and the Interior, to report upon the merits of the 

 works already executed, and to propose the best means of perfecting what 

 had already been commenced, and of completing this great undertaking. 



This Commission, amongst other important suggestions, give it as their 

 opinion that the stability of the upper part of the digue could not be 

 reckoned upon without the employment of larger stones than those hitherto 

 used, and which had become much diminished in size by their frequent 

 displacement and friction ; that large blocks, 51 to 09 centimetres cube had 

 a presumed stability sufficient to resist the action of the sea, and that this 

 stability would increase with the volume of the blocks of stone employed. 



The general dispositions recommended by the Commission of 1792 were 

 adopted by the Government, upon the strength of the advice of a committee, 

 composed of several general officers and admirals, and engineers of the 

 greatest eminence in the three departments of War, Marine, and the In- 

 terior. 



It now only remained to determine the height to which it was necessary 

 to elevate the breakwater, in order, not only to procure smooth water in 

 the roadstead, but at the same time to afford every possible protection to 

 fleets and convoys against the attacks of the enemy. 



It was the unanimous opinion of all the practical persons who had 

 observed the etl'ect of the se.i upon the digue since its commencement, 

 that at low water, in bad weather, from seaward, the roadstead was per- 

 fectly calm ; but that, as the tide rose, it became troubled ; and that, two 

 hours before and after high water, when the wave appeared to acquire a 

 greater force in breaking upon the breakwater, the vessels, particularly 

 those near it, were much troubled by the sea. 



After having noted the height above low-water mark to which the sea 

 reached two hours before and after high water, it appeared a constant rule, 

 that when the waves became troublesome to the ships in the roadstead, the 

 sea had risen 4 metres 70 centimetres. 



Hence it was naturally concluded that it would be advisable to carry 

 the summit of the breakwater at least 4 metres 70 centimetres (14 It. in.) 

 below the level of the highest tides ; that is to say, to 2 metres 44 centi- 

 metres (7 It. 6 in.) above the level of the lowest tides, the rise in the sea 

 outside being calculated at 22 feet, or 7 metres 15 centimetres. 



But viewing the great advantages which would result from its being 

 carried up to the level of the highest waves, it was nut hesitated to propose 

 its elevation to 9 feet (2 metres 92 centimetres) above the level of the high- 

 est sea outside; that is to say, to 31 feet (10 metres 7 centimetres) above 

 the lowest tides. 



But the revolutionary troubles put a slop to all further proceedings con- 

 nected with the recommendations of the Commission of 1792 ; and the 

 completion of this vast enterprise appeared to be indefinitely delayed, 

 when, in November 1800, a new government turiii-d its attention to this 

 important object of public utility, and named a Commission, upon whose 

 report in 1802, the government directed that the centre of the breakwater 

 should be elevated 2 metres 92 centimetres above the level of the highest 

 tides, with a breadth of 195 metres, whereupon to construct a battery of 

 20 pieces of artillery of the largest calibre ; and that the extremities of 

 the breakwater should be, ultimately, similarly constructed for a like 

 purpose. 



This was recommended in consequence of the great distance (7,017 me- 

 tres) between Forts Koyal and Querqueville, which was deemed too great 

 to prevent enemies' ships from anchoring to the north of the breakwater, 

 thence firing on vessels within the roadstead, themselves being beyond 

 good range of the forts. 



At this period (1802) those works previously undertaken, which had 



