1S40.] 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



359 



be introducetl, tliat the timber viaducts weve the most economical. In ordi- 

 nary heights of 50 or 60 feet, and mth arches of less span than 100 feet, and 

 particularly in countries presenting faciUties for construction of stone, these 

 latter would be undoubtedly preferable; but when the height of the con- 

 struction became great, the great expense for the centering for arches of 

 masonry, and the multiplication of the number of ]ners, in order to keep the 

 span of the arches to a moderate size, greatly increased the expense, and 

 threw the balance vastly in favour of the timber. Mr. Vignoles instanced 

 the Ribble Viaduct on tlie North Union Railway (a model and description of 

 which is in the Model Room of tlie -Association'), which was about 50 feet 

 high, with five large arches, of 120 feet span, and had cost 60^. per lineal 

 foot; whereas, in another place, a timber viaduct, of 140 feet high in tlijc 

 centre, and averaging 100 feet high, with arches of 130 feet span, and ex- 

 tending for a lengtli of nearly 2000 feet, was proposed, which would not ex- 

 ceed in price 201. jier lineal foot, the breadth of roadway being, in both cases, 

 28 feet for a double line of rails. Mr. Vignoles stated, that in extending 

 hues of railways through the west of England to the packet stations, through 

 the mountains of Wales for a communication between London and Dublin, 

 and through many parts of Ireland, along the lines laid out by him for the 

 Government Railway Commissioners, the timber viaducts would, from their 

 cheapness, enable the works to be entered upon, which the great cost of stone 

 would quite forbid ; and he concluded by calling on his fellow engineers to 

 turn their attention to this while laying out new lines, and to take bolder 

 steps across the valleys, relying on the timber viaducts to accomplish their 

 objects. 



Mr. Blytli thought that Jlr. Vignoles had over-estimated the expense of 

 stone, which Mr. Blyth knew had been executed at about 25/. per foot. — Mr. 

 Vignoles replied, that it was seldom that stone could be had at so small an 

 expense ; when the span is large, and the height great, it is much more costly. 

 — Mr. Smith, of Deanston, agreed Nvith Mr. Vignoles, but did not think that 

 planking was the best method, as it woidd not stand so long. A wooden 

 bridge should be so constructed, that any decayed part could be taken out 

 and replaced. 



THE THAMES EMBANKMENT. 



The Select Committee appointed to consider the Petition of the Cor- 

 POR.A.TIOX of London- relative to the Embankment of the River Thames, 

 and to report their observations and opinions thereupon to the House, to- 

 gether with the best means of carrying the same irito effect ; and to whom 

 several Petitions relative to the measure, and Reports of former Committees, 

 were severally referred ; — have considered the matters to them referred, 

 and have agreed to the following Report : 



The Committee have met and proceeded to examine a Plan and Estiiuates 

 of the proposed Embankment, submitted by Mr. Walker and Mr. Higgins, 

 and other witnesses : that several petitions for and against the measure hav- 

 ing been referred to the Committee by the House, and many other witnesses 

 both for and against the intended plan being proposed to be examined, the 

 Con.imittee are obliged, by the near approach of the prorogation of Parlia- 

 ment, to conclude the inquiry without the examination of many i)lans for the 

 embankment of the river, or the consideration of any plan for the improve- 

 ment of the navigation, without any alteration of the present line of emljank- 

 ment. Upon the general subject, therefore, of the improvement of the navi- 

 gation, with or without any embankment, they give no opinion in the present 

 state of the inquiry. 



29 Jvly 1840. 



Abkidgement of the Evidence. 



Jiniu's IValker. Es J., was examined and stated that he has been profession- 

 ally acquainted with the river Tharaes, in reference to the subjects of inquiry, 

 for the last 30 years he has been employed, either as assistant or ])riiieipal 

 engineer, at rhe" greater part of the dock's that hive lieen constructed in the 

 port of London. In ISIU he constructed Vauxhall Bridge, and in 1821 his 

 attention was called rlirectly to the etiecis that the then proposed removal of 

 London Briilge would ba\e on tiie river Thames. He has been almost con- 

 stantly employed on works of a similar nature ou Ihe Thames from (hat time 

 to the present day. He was called in by the comrailtee for letting ihe 

 Bridge-house estates in 1821, n.long with Iiis friend -Mr. Leach, to report on 

 the effect that the removal of Londc n Bridge would have on the water of the 

 river Thames. He did not think that ballasting h'ls done much good; it is 

 done for the purpose of obtaining ballast, and it is only v.here Ihe ballast is 

 good that the are iging' engines have got io work ; that has no; much regard 

 to the inlerests of the navigation. It does nothing to take away the shoals. 

 At present the water ebbs so low in the river, above bridge, that in some 

 parts of it, whore the width is very great, the shoals are periectly dry for the 

 greater part of Ihe widlh across the river; mostly in that part of ilie river 

 above Waterloo Brid;ie and the neighbourhood ; between Westminster and 

 Waterloo Bridges and below. The dredging vessel above bridge is used 

 chiefly for obtaining gravel lor roads, not for ballasting- ships and similar 

 [Turposes. Tlie effect of the removal of London Bridge opcra.ing in the way 

 he lias stated, increased the ve'ocity of the current through Blackfriars 

 Bridi^'e, and had nearly undennined the p ers ; so that bv going down, which 

 he did in a diving helmet, he could put his leg under the caissoon bottoms, 

 under the platibrm on«h:ch the bridge stands; the consequence was that 

 Ihe city, partly throauh that cause, and partly through the decayed condi- 

 tion of the stone, ordered a survey to be made, and an esiimate ; and since 



that time, five of the piers have had coffer-dams put round them, and the 

 foundations exiended down to about 11 feet below- the old bottom, as re- 

 gards Westminster Bridge, although a gr at deal of trouljle had been taken 

 for a great many years in supporting it, the Commissioners of Westminster 

 Bridge, also for the same reason, have commenced strengtheninc; tlie piers in 

 the same wiy as has been done at Blackfriars Bridge, bv coffer-dams ; he 

 considers that both of them are the effect of the removal of London Bridge. 

 He did not think that any increase of ballasting v.ould prevent the accumula- 

 tion and increase of shoals, because while thi^river is so unequal in width as 

 it is now, yiu may keep ballasting, but the velocitv being slow at ihe wide 

 parts, you v:\\\ have a settlement always taking r^'ace there again, an 1 then 

 you must go on constantly with the ballasting. " The/irst thing to be dene is 

 to regulate the width of the river. Tlie plan of the river wdiich is before 

 von will show you, ihat in places now between London Bridge and Vauxhall 

 Bridge the river is double the width that it is at other places. The effects by- 

 London Brid^.e being removed since 1821. are what he has before described, 

 to deepen naujiow- places very much, and to cause large shoals in the places 

 where tiie river is so very wide. To give the Committee an idea what the 

 present width is, he stated, that the width now opposite the Penitentiary is 

 600 feet at hipli water : opposite Millbank. to the Bishop's-walk, it is 1,050 ; 

 opposite the Roard of Control it is 1.200 ; and opposite Buckingham-terrace it 

 is 1.480. Then it keeps narrowing by ilegrees, uniil belo'\- Soulhwark Bridge 

 it is 720, and at London Bridge the v,-aterway is 690. While Ihe river is so 

 unequal as that, no dredg-ng would do much good. If you (Iredged so as to 

 get proper depths for navigation in the wide parts, you'have a settlement of 

 mud, and a constant removal of that again, or an accumulation of shingle to 

 (ill up those cavities. The idea here was. first to endeavour to get something 

 like a regular section, not strictly increasing in width by degrees, but ap- 

 proaching to il as far as could be done consistently with the value of the 

 property on the sides of the river. The waterway of Vauxhall Bridge itself 

 is 702 feet ; the width of the river 200 or 300 yards above is G80 feet at high 

 water, between the wharfs. He does not consider the whole of that water- 

 way useful for the purposes of navigation as a thoroughfare, but it is for 

 the' general purposes of trade, that is to say. that the barges can go up to the 

 wharf-side, and can go away again at high ■« ater at all times. There was an 

 apprehension that the present embankments that have been carried out, such 

 as that one at the House of Commons and others, would have left in the 

 parts of the river near it a considerable quantity of mul, and the proprietors 

 of property above bridge had a clause introduced into the Act for building 

 the Houses of Parliament, keep ng open their claim for compensalion in case 

 of damage being done. I^e has. from time to time, as employed by the Com- 

 missioners of Crown Lands, sections taken of the states of the ground at dif- 

 ferent times, and the fears of those parties have proved to be very much 

 over rated ; the increase is not so great as he expected. The increase is very 

 variable ; perhaps in some places it is lower, and in other places higher, but 

 as a general posiiion he does not think there is much increase. There ai'e 

 now deposits in consequence of the embankments. The coffer-dam around 

 two of the piers of Westminster Bridge tended to send the water over to the 

 opposite side, and to cause a settlement of mud on Ihe Middlesex side : that 

 colii=r-dam is now removed, and the opening which was closed by the coffer- 

 dan-i is deeper ami better than ever it was. The deposits have been between 

 high and low-water mark. The effect, opposite the projection itse f, is to de- 

 crease the deposits by narrowing them ; but the effect also is to cause the 

 settlement of mud above and below. The effect that would otherwise be pro- 

 duced is much lessened by the constant passage of steam-packets up and down 

 the river. "The mud is kept in a stateof suspension instead of being deposited. 

 What tlie embar.kment would have tended to have done has been prevented 

 or removed by the wash of the steam-packets. The removal of the coffer- 

 dun from the western arch of Westminster Bridge will tend to remove the 

 deposit 'hat li-.s taken place in the course of last year : and when the coffer- 

 dam in front of the new- Houses is removed Cwhicli it will be when the Houses 

 of Parli.iment are finished), with the large quantity of ground «hich he had 

 put out for the purpose oi'sec^iring the cofler-dam, that will tend to bring the 

 current over totlio Middlesex side. He hopes the effect of continuing the em- 

 bankment will be, if properly done, to remove the shoals. The idea would be. 

 whether bv embankment or otherwise, to deepen the river b>- the removal of 

 the shoals', and to apply those shoals to filling up behind the embankment. 

 He contemplates two operations, both deepening the river artificially and 

 building the embankment; the embankment could not be made »i;hont the 

 material which will be taken from the bed of it to fill in behind the embank- 

 ment, which will have the eflect of deepening ihe river. Deepening the river, 

 the supply of water remaining the same, will tend to throw a greater quantity 

 of water within a certain part of the channel, but it will not be at 

 Ihe expense of that side of the river where there is no embankment ; the em- 

 bankment being to be Ibrnied close up to low-water mark on the north side. 

 There will be more water on the south side ihan there was before. 



Mr. Walker explained that it is not only the land floods coming down, 

 that chiefly furms the cun-ent of water in the river Thames opposite Lambeth ; 

 but it is also owing verv much, except in extreme floods, to the tides. Now, 

 Mhetherit be from tidal water, or from land Hoods, the effect of narrowing 

 the river on the north side would be, as there is a given quantity of water to 

 come down during the land floods, to press that water more over to the south 

 side, and to increase the velocity. With land floods the quantity is given; 

 that is to say. it is fixed, whether the opening be large or small. With regard 

 to tidal water, it depends on the space to receive the tidal water ; but the 

 eflect in any way would be to give greater velocity, and tend to the removal 

 of mud from the shoals on the south side. Where the river is very wide and 

 straight, there is a very considerable quantity of mud, three, four, or five 

 feet and more ; at other places, at Waterloo Bridge, for instance, although 

 the width is very great, there is not so great a quantity of mud, because the 

 flood -tide rather takes that oft. Mr. Walker stated that his evidence dven 

 referred to one side of the Thames only. The ultimate scheme is to embank 

 both. It may be done wiih one side only, but not so complete as with both 

 sides. Although he uses the word embanking, the Committee must not un- 

 derstand that there is an intention, or that it is practicable to embank both 



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