318 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



I July, 



much of their force caught by the recediDR of the previous wave, so as 

 rarely to sirikp with much force against the wall itself. 



" There can he no doubt but that a slope Could be given to a breakwater 

 that woulil be very secure. 



" In Holland, the shores, even of sand, are in many parts secured against 

 the whole force of the North Sea liy a surface cortliug of mere clay and 

 straw, but then the ini liualion is exceedingly gentle quite to deep water, 

 not more, I apprehend, than 1 in IS or 1 in 24. As the material is in- 

 creased in sixe and weight, it is to be presumed that this blope may be in- 

 creased." 



4. Sir Henry De la Beclie is adduced as an advocate for the upright 

 ■wall. Now the theory of the upright wall rests entirely upon fhe assump- 

 tion that waves have no progressive forward movement or motion, or per- 

 cussive force, in acting upon ereclions in the sea, or on coasls, clifts, or 

 beaches. But Sir H. Ue la Heche expressly states, that seas in heavy 

 gales of wind are urged onwards in the direclion of the winds which raise 

 ihem ; that waves iu a breaking slate possess enormous force from the 

 weight ami velocity of the water thrown forward ; and the following ex- 

 tracts from his very able work, " How to Observe Geology," show that 

 he has been erroneously cited, or that he expressed himself in an unguarded 

 manner, when he asserted that upright walls resembling elilTs, are more 

 Capable of resisting the percussive efl'ecls of waves and seas than slopes." 



In the very able work which this eminent geologist published, he de- 

 livers the following rules as the result of what he had observed and ascer- 

 tained with respect to the action of the sea :^ 



" Properly to estimate the ell', cts of this power, the observer should be 

 present on some exposed coast, such as that of llie western part of Ireland, 

 the Land's End, Cornwall, or among the western islands of Scotland, dur- 

 ing a heavy gale from the westward, and mark the crash of a heavy Atlan- 

 tic wave when it strikes the coast. The blow is sometimes so heavy that 

 the rqck will seem to tremble beneath his feet. He will generally lind in 

 such situations, that though the rocks are scooped and caverued into a 

 thousand fantaslic shaijes, they are still hard rocks, for no others could 

 continue long to resist the almost incessant action of such an abrading 

 force. Having witnessed such a scene, he will be belter able to appreciate 

 tbe elTecis, even though the waves be far inferior iu size, upon the softer 

 rocks of other coasts. 



"The observer should carefully remark the direction of the prevalent 

 winds, and the proportion of those which send the greatest waves, or seas 

 as they are termed, on shore, in order that he may duly appreciate the loss 

 of coast sustained iu those direclious where the force of the breakers is 

 greatest and most incessant. 



" It must not, however, be forgotten that coasts where breakers reach 

 the dill's at high water, are frequently protected by beaches at low water ; 

 and that therefore they are removed from the abrading power of tbe waves, 

 during all the time that they break on the protecting beaches, a lime which 

 varies with the varying state of the tides, and the state of tbe weather 

 generally, 



"Other encroachments are made by the fall of masses of cliff undermined 

 by the waves, the cohesive power of tiie ruck not being equal to its weight, 

 or the action of gravity downwards. If a rock be even sullicienlly cohe- 

 sive iu the mass, as to admit of cousiderable excavation without falling, a 

 time must come, if the breakers continue to work on iu the same direclion, 

 when the Weight of the superiucumbeut mass would be such that it must 

 fall. 



" Where, however, a great mass of cliff does fall, in the manner noticed 

 above, the observer should direct his allenlion to its conservative inlluence. 

 To appreciate this, he will consider the hardness of the rock, the position 

 into which it has fallen, and its new power of breaking the waves farther 

 from the coast. If the mass of fallen rock be slratilied, much will depeud 

 upon tbe face presented to the breakers; for if it fall so that the plane of 

 the beds remains sloping seaward, it will act as a well contrived wall 

 erected to defend the chlf; but if the beds sliould be exposed vertically 

 after the fall, the fiiliire destruction of the mass would be far more rapid, 

 and its conservative inlluence consequently less." 



5. No one knows betler llian 1 do ti.e ability, the zeal, and the intelli- 

 gence which iMr. Harlley has displayeil in the construction of the Liver- 

 pool Docks, and the hydraulic woiks m the Hiver Mersey ; in slating his 

 evidence, as that of a practical man, in favour of th"-- upright wall iu the 

 open sea in Dover Bay, I think it best to let him speak for himsell'. 



Qucsliiin. •• Vou say jou prefer an upright wall to any other form fur a 

 breakwater; do you know any certain instance of the jiositive experi- 

 ment of a wall which has stood the test of time in such an exposed situa- 

 tion, and on such a mouslrous scale as Dover Harbour may require? — 

 Answer. I do not, 



" Is it merely matter of opinion? — That is all. 



"This perfectly upright wall iu Dover Bay in seven fathoms water is an 

 experimental measure jou admit ,' — Unite so as respects myself, 



" Willi respect to the time lliat it would lake lo make a breakwater, is 

 that opinion formed upon any knowledge of Dover, or the diUicullies of 

 making a wall at Dover? — No, it is only founded upon a supposition of 

 what the sea is in general, and supposing I was lo attend lo it myself, and 

 had nothing else In do ; but it is a vaRue sort of idea. 



" A'oii are not acquaiiiled with the locality? — No, not sufUrienlly ; I 

 have becu there two or three limes. 



" Have JOU ever built a wall yourself in such deep water as that? — No, 

 n''ver." 



6. My gallant aad highly esteemed friend, Major-general Pasley, gives 



the following account of his conversion lo, or adoption of, the theory of the 

 upright wall: "For many years I paid no attention lo this sulject, but 

 thought that the long flat slope adopted at Hlymoulh Breakwater must be 

 the best form for resisting the sea, not only from the reputation of the 

 eminent engineer and naval offirers by whom this construction was pro- 

 ])osed, but also from ilie circumslance of iis having been approved and car- 

 ried into execulion by order of the (iovernment of that day. But iu the 

 year 1842, \\lien this question was publicly discussed at one of the meet- 

 ings of the loslilutiou of Civil Engineers, at which I was present, aflcr a 

 paper of Lieutenant-colonel Jones, lE.E., had been read, iu which lie gave 

 the preference to ujiright wails, as being much more secure than break- 

 waters or flat slopes, aud staled his reAsons for this opinion, the arguments 

 in favour of the former appeared to me to preponderate. I have since given 

 the subject iiiuch attention, and iia\e made inquiries and observatious, 

 which have confirmed me in this impression." 



7. Captain Vetch is the next autliority cited in favour of the upright 

 or nearly upright wall, both from theory and (uactical observation. On 

 account of the extraordinary dilliciilties of constructing a harbour of 

 refuge in Dover Bay, he thought that ihe best mode of executing such a 

 work was by the system of caissons which he proposed. With respect lo 

 the combination of a slope wilh an upright or nearly upright face for Ihe 

 superstructure, he Captain Vetch, said it would be liighlj advantageous ; 

 that it would obviaie a great many objections lo the present condition of 

 the Plymouth Breakwater; it woul.l prevent the waves breaking over, 

 and would give security to erections on the breakwater itsell'. The works 

 now going on at Cherbourg, which had been erroneously considered to be 

 an abandonment of the slope iu favour of the upright wall, is only a com- 

 bination of both ; this he thinks a great improvement, and adds, that such 

 a breakwater at Dover would he very superior lo one enlirely sloping. 

 Captain Vetch recommends brick in cement for face work, ami sug>'esls 

 blocks of brick hrmly agglolinaled into a mass by means of a cheap flux 

 between the joints ; the mass of brick blocks being subjected to the re- 

 quisite beat by iiieaiis of flues or otherwise, 



b, M. M. Reibell is the next authority adduced in support of the up- 

 right wall ; and a sketch, of which the annexed is a cojiy, is inserted in 

 the Proceedings of the Commissiou lo sustain, as it would appear, the 



proposition of the upright wall, which it is inferred the French engineers 

 as a biidy, approve, and would adopt, if the breakwater in Cherbourg Bay 

 were to be commenced de voi'o. 



Captain Washington, in his report on the breakwater at Cherbourg 

 states, that " iNI, Keibell, the present engineer, is dec'idedly in favour of au 

 upright wall, and recommends the form shown iu Ihe annexed sketch as 

 the best for opposing the shock of the waves." 



9. Mr. Brunei is next adduced as having giren his opinion in favour of 

 an upright wall for the constrnclion of breakwaters. But Mr. Brunei was 

 uot examined before the Commission, and the only opinion which he has 

 given upon tiiis subject is that contained in the annexed exlracl of a letter 

 from Mr. Brunei, adilressed to the Cliairman, dated l!)tli .lune 1S44 ; 

 " Upon one point upon which 1 understand the Coiiiiiiis::-ioners to have 

 sought ail opinion. I h^ve no hesilali.<n in expressing my concurrence in 

 those which i am told have been generally expressed in favtiur of vertical 

 sea-walls, in lieu of slopes, where the nature of the material to be used, 

 aud other circuiustances, admit of such a plau being elliciently and ecouu- 

 mically carried out," 



10. Mr. Bremner is next adduced as an authority in favour of the up- 

 right wall, 



Willi the greatest possible respect for all these able and eminent men, I 

 must say, that I do uot lind any tiling iu what they have addiicefi that can, 

 in my judgment, warrant the adoption of the mode of constnicliun which 

 they recomniend ; it does uot rest upon any proved principle, is untried 

 upon any sutlicieiit scale to justify its adoption in a great national under- 

 taking, and all agree in designating it ex|U'rimeutal. 



When I lind it staled, in the summing up of Ihe Commission, that Ihe 

 opinion of Mr. Alan Seveusou in favour of a sloping breakwater is the 

 " sole excepi ion" lo those of the other men of disiio:;nisli-d sci'Miee and 

 practical observation, wlio have been called upou Iu advise the Commissiou 

 on Ibis importan! subject, — I feel bouiul to imerpose against the conclusion 

 arrived at. Sir John keniiie, Mr. (ieorge Kennie. iMr. Ciiliiti, Mr, William 

 Stuart, as well as Mr, Alan Stevenson, who all disapprove of auy alteinpl 

 to construct an upright wall in Ihe ojien sea at Dover; and they distinctly 

 express Iheir opinion, apprehension, or conviction, that such allempt would 



