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THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



107 



us certtiinly did the bottom wear and assume an irregular deep rutted 

 surface, so that after all these schemes he was constrained to return to 

 the old system of staunching the current by the sinking of ships, ponts, 

 and bags of chalk. The only new feature which he introduced into 

 the plan was the fixture of enormous hair bags filled with chalk (some 

 ()fthem3Ufeet in length) to the vessels bottom, which bags it was 

 expected would have adapted themselves to the form of the bottom, 

 and thus preserved a closer connection than had been effected before. 

 He accordinglv carried out his scheme, having sunk two vessels and 

 the large pontoon which he had previously made, and he also sur- 

 rounded the whole fabric with enormous quantities of chalk. In ad- 

 dition to this he had placed in the banks a little below the breach, two 

 sluices which were intended to have relieved the pressure, but which 

 according to Captain Perry could not from their construction and level 

 have been of anv service. The very first tide after the vessels had 

 been sunk, operated with such energy on the bottom, that the whole 

 fabric was totally destroyed by the second day after. The vessels 

 laden with chalk and rubbish were thrown up, and the enormous pon- 

 toon gave the finishing blow by starting up and tearing to' pieces the 

 pile work and planking. 



Here ended Mr. Boswell's services, and the trustees appointed by 

 the bill having nominated a committee, inspected the ground and drew 

 up a report dated November 7, 1715. The following soundings taken 

 by the committee and given in their report are as follows : " on the 

 \vestside 20 feet below the works to the south, 40 feet deep. On the 

 south side 20 feet from the stern of the Abindon (one of the ships sunk 

 in the said breach, 30 feet. On the same side, 15 feet from the stem 

 of the Recovery, (another ship) 18 feet. Ten feet south from the 

 piles on the east side of the breach IS feet. Between the ships and 

 the piles on the west side 29 feet. Betwixt the works to the north- 

 ward near the piles on east side 24 feet. At the end of piles on east 

 side 19 feet. Fifty feet north from said piles 31 feet. Fifty feet 

 farther north 5>l feet. Twenty-five feet north of the piles on the west 

 side 26 feet. Fifteen feet north from piles in west side 14 feet. Close 

 to said piles on west side 20 feet. Coming about the piles to the 

 southward we find these depths following, viz., 29, 24 and 18 feet." 



What sort of settlement was made with Mr. Boswell does not ap- 

 pear from the narrative, but new offers were obtained. Captain Perry 

 gave in an account of his scheme, which was this. To have a sluice 

 made in the embankment with a trench connected with the backwaters. 

 To drive a row oi dovetailed piles across the gap, leaving their heads 

 not more than IS inches or 2 feet above low-water mark ; so that in 

 driving these piles little or no difficulty would be experienced from 

 the current. Forty feet from the row of piles on either side a sort of 

 low coffer-dam 18 or 20 feet broad, to be formed of piles and boarding, 

 and to be filled with chalk to prevent the toe of the embankment from 

 spreading. On the outside of these coffer-dams a wall of chalk to be 

 made as a farther security. The dam itself to be composed entirely 

 of earth, and in the course of the erection care to be taken always to 

 shut the sluice when the backwater falls to the level of the top of the 

 work. In this way there will at no time be a higher face for the 

 water to flow over. 



This was evidently a judiciously contrived scheme, and shows that 

 the projector of it had a just conception of the nature of the difficul- 

 ties he was to contend with, which were a soft, unstable bottom and 

 a powerful current of water. He was well aware that a dam of the 

 thickness he contemplated would easily sustain the pressure of back- 

 water, although from its being composed of soft materials, he could 

 not expect it to withstand the action of water rushing over it. Ex- 

 perience had proved that such materials as chalk could not from the 

 large interstices necessarily existing between the pieces, form anv- 

 thing like a water-tight dam, and if they had, the softness of the bot- 

 tom was enough to render such a plan impracticable. The first grand 

 points were to secure the treacherous bottom, and make a heavy and 

 water-tight dam. These difficulties were well provided for by the 

 use of dove-tailed piles and a clayey soil. The second point was to 

 prevent the ebb and flood tides from rushing over the top of the dam 

 when it was in progi'ess ; this difficulty was removed by keeping the 

 backwater constantly on a level with the top of the work. 



After much communing and trouble on both sides, a contract was 

 entered into with Captain Perry, who was to perform the works for 

 i:25,000, he being bound to advance £5000, and to expend that sum 

 on the works, after which he was to be supplied by the trustees. If 

 the work were unsuccessful, the £5UU0 was of course lost to Captain 

 Ferry, or, rather, to the friends who had advanced it. Should, on the 

 other hand, the work be successful, but be rendered very costly from 

 any unforeseen accident, he was to be recommended to the conside- 

 ration of Parliament. 



After all this had been settled, Captain P. seems to have been much 

 annoyed by Mr. Boswell and a host of mathemalicians, who declared 



his plan impracticable. He, however, came through their hands, ac- 

 cording to bis own account, non sine gloria, as well as tlirough the 

 ordeal of sundry examinations and meetings. 



No time was lost in commencing the work ; but the sluice, from 

 the softness of the ground, was not carried to its contemplated depth, 

 which incurred the necessity of another being made. From some 

 cause or other matters seem to have been mismanaged, for it was not 

 until the spring of 1717 that the second sluice was completed, and the 

 breach was not stopped till June. For this tardiness he pleads seve- 

 ral excuses, but he does not succeed in satisfying the reader as to his 

 promptness. The time for completing the dam had now nearly ap- 

 proached, and his friends who had advanced the money, became im- 

 patient, and so importuned him to push on tlie work, that he allows 

 he was persuaded to admit stuff of an inferior binding quality in the 

 formation of the dam. A great deal of bad earth was also put in 

 without his knowledge, when the men were working at night, and liis 

 assistants, five in number, seemed rather to conspire against him than 

 to back him in any of his difficulties, so that what between grumbling 

 friends, rebellious assistants, and an impatient public, he was con- 

 strained to collect together all the force he could muster in the neigh- 

 bouring country, in spite of the high wages of 3Gs. per week. These 

 labourers, assisted by men from the royal yards of Woolwich and 

 Deptford, soon made a satisfactory difference in the appearance of 

 the work, but a most unsatisfactory difference in its quality. Hitherto 

 each tide's work had been made in offsets or scarcements, about 7 feet 

 broad and 3 feet high, these supported by piles and planking on the 

 side, and protected by reeds on the top, had been able to resist the 

 action of the tide when it came in. One of the assistants, however, 

 proposed during the neaps to set all hands to work and make a narrow 

 wall of earth, unprotected by reeds or planking, and build it so rapidly 

 as to get it above the level of the springs before they should come on, 

 and thus at once to exclude the tide from the marsh. Captain Perry 

 unfortunately gave in to this proposal, trusting to the tide's being of 

 its ordinary height. There happened, however, an extraordinary tide, 

 occasioned by a storm at N.W., which tide rose about 6 inches higher 

 than the top of the little wall, and pouring over it, soon washed it 

 down, and the water thus widening its inlet, rushed over in such 

 volumes, that in the course of two hours the dovetailed piles were 

 laid bare. 



When Captain P. observed the tide rising with unprecedented ra- 

 pidity (which it did), he heightened the little wall with piles and 

 boarding set on edge on the top, but the water insinuating itself be- 

 tween the boards and the earth, led to the calamity we have men- 

 tioned, and which the Captain says was due merely to the fortuitous 

 occurrence of an extraordinary tide. Men were employed in digging 

 down the earth, and otherwise easing the passage of the water over 

 the dam, as well at the first inbreak as at subsequent tides, by which 

 means the violence of the current was speedily checked. 



This accident, as might have been supposed, caused many reports 

 about the general insufficiency of the work, and the erroneous prin- 

 ciples on which it had been carried on. This did not, however, deter 

 Captain P. from proceeding with the repair during the winter months, 

 and in raising the dam this second time, he was a great deal more 

 scrupulous about the quality of earth used in its formation, and in the 

 end of June, 1718, " the tide was again turned out of the levels in the 

 time of neap as before, only that the work, after the tides were turned, 

 was now continued to be raised by set-offs with piles and boards, and 

 well covered over at the top, so that though a thin body of water did 

 several times pass over into the levels, it was easily let off by the 

 sluices. The trustees now visited the work, and expressed them- 

 selves satisfied with the manner in which this part of the work had 

 been accomplished. After their visit he dammed up the two canals 

 communicating witli the sluices, and any subsidence of the dam he at 

 once made up with new stuff The work being now in an apparently 

 safe condition, the Captain left for Dover, where he was to report on 

 the Harbour, and on his return he was seized with ague, and when he 

 was recovering, but was still confined, on the morning of the 30th of 

 September, 1718, a message was sent to him conveying the mortifying 

 intelligence tliat the tide had again demolished the work. In spite of 

 his ague he at once visited the spot, and found the sluice dams stand- 

 ing and the sluices shut, and, in short, nothing done towards easing 

 the passage of the waters. He immediately summoned as many hands 

 to his assistance as the neighbouring country could, on such short 

 notice, produce; but the water had made such havoc, that in six tides 

 about a hundred feet of the dovetail piles, &c., were torn up and 

 carried away, and in one place there was about 20 feet greater depth 

 than there was before the work was begun. 



How this accident occurred was for some time a mystery, but it sub- 

 sequently came out that the watchman had, instead of attending at his 

 post, been reviving his frozen carcase at a neighbouring beer shop. 



