TO 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[Mabch, 



the Victoria Bar at the best time for action on it. By the con- 

 struction of the sluices, the «ater, instead of l)einff pouretl down 

 to tear ii]> the bottom of the basin, will be sent alonjj in a sheet, so 

 as to prevent the silt from depositing itself. This sheet will lie 

 sent below the water in tlie basin, and Mr. Rendel thinks it will 

 act to sweep the silt 2,000 feet. 



It will be seen tliat by blocking up the Pool and inclosing- the 

 greater ])art of the strand, a considerable body of tidal water is 

 dis]jlaced. 



Mr. Rendel expects by straightening the shore on the Birken- 

 Iiead side that the access of the tide to the upper Mersey will be 

 improve<l, and that the scour being increased Pluckington Bank, 

 on the Liver|iool side, will be reduced, a better entrance will be 

 made to AVallasey Pool, and a more favourable action will be 

 exerted on the Victoria Bar. 



The plan seems open to the objection that injury must ensue 

 from the tidal displacement at Birkenhead, particularly as by the 

 construction of new docks on the Liverpool side a further displace- 

 ment takes place there. 



Mr. Rendel says that this is of no importance in the case of the 

 Mei-sey. If the river were of a funnel shape an obstruction below 

 would impede the passage of the tide up, and diminish the quan- 

 tity of water available for scour. He allows that injury %vill ensue 

 if an obstruction takes place in the up])er Mersey, because 

 there will be less room for the water to accumulate ; and there- 

 fore there will be a less body to scour down on its ebb. He 

 contends, however, that the displacement on the neck of the flask 

 is of less importance, as the water there is of less power for 

 the scour than the water returning from the upper Mersey. Tlie 

 tide will always have time and power to force its way up the neck 

 to supply the reservoir in the upper Mersey ; and the state of 

 the channels in the neck is determined by the state of the upper 

 Mersey, and not of the neck. He contends on the ground of the 

 improving state of the Victoria Channel, and, notwithstanding the 

 dlsjdacement by the docks at Liverpool, that operations at the 

 neck cannot injure the Victoria Channel. Pluckington Bank, he 

 affirms, is formed by the set of tlie current on the irregularly- 

 shaped shore of Birkenhead. By sti-aightening the Birkenhead 

 shore, and making it parallel with the Liverpool shore, the neck 

 will be made more efficient, the tidal body passing up will deepen 

 it, and Pluckington Bank will be worn down, though he does not 

 say it will sweep it away altogether. 



Tills is really a summary of the harbour question; and we 

 believe we have put it with sufficient succintness and clearness 

 to enable our readers to exercise their judgments upon it. 



The arguments and researches of Mr. Rendel in support of his 

 case are well worthy of perusal, for they exhibit very able treat- 

 ment and high powers of mind. It is in the preservation of these 

 that the ]iractical value of Mr. Webster's book consists; and it is 

 fortunate that the editorship fell into Mr. Webster's hands; for 

 as it is chiefly an abstract of the evidence, a mere lawyer would 

 have got rid of the practical points, and the book would not have 

 been of the least service to engineers,-^whereas it is one which 

 will be usefully added to the library of every member of the pro- 

 fession. 



The formation of a liarbour at Birkenhead is not new to en- 

 gineers, for, in 1828, Telford, Stevenson, and Nimmo were em- 

 ployed on a plan by Mr. Laird, sen., and Sir John Tobin, and re- 

 commended the formation of a canal from Wallasey Pool to the 

 Dee at Hilbree island, near its mouth, so as to get another access 

 to the sea. This is a resource which Birkenhead still has, and 

 which with its progress it will avail itself, but which will not 

 checkmate Liverpoid. Liverpool has, by the plan proposed for an 

 out-harbour at Formby Point, a cheap means of providing more 

 efficiently for all that could be done by a new sea outlet to Bir- 

 kenhead. Formby Harbour could be made cheaply; while two 

 short cuts to the Leeds and Liverpool Canal, and to the Liverpool 

 and 6outh])ort Railway, would allow of goods being carried 

 cheaply and quickly into the Liverpool docks; and for steam traffic, 

 Formliy Harbour would beat the Hilbree Canal. Mr. Rendel'splan 

 may be considered as novel in its whole arrangements and treat- 

 ment. Mr. Telford in looking at the Mersey is reported to have 

 said : " Tliey have built Liverpool on the wrong side of the river." 

 We shall now take some stray gleanings from Mr. Webster's 

 book. Lieut. Walker, R.N., says that Pluckington Bank is caused 

 by two opposing tides or eddies from Wallasey Pool meeting and 

 causing tlie silt held in suspension to deposit itself. The 

 straightening of the Birkenhead shore would remedy this. 



Birkenhead, we may note, besides being the deep-water side, 

 has the advantage of being the weather-side ; while the docks on 



the Liverpool side, most exposed to the waves breaking over the 

 sand-banks, are the most liable to silt up. 



The area of the float at a high tide is 208 acres, the frontage 4^ 

 miles. In the dam, .Mr. Rendel proposes a pair of tide-gates of 70 

 feet o])eiiing, the level of their sills being the same as tliat of the 

 Prince's dock, at Li\'eriJool. This float would allow steam-tugs t») 

 enter, which is not the case at Liverpool. Mr. Rendel calculates 

 on the movement of the steamers likewise in keeping his channels 

 clear. Besides the tide-gates of the great float, Mr. Renilel pro- 

 poses a lock of 50 feet wide and 200 feet long, which could be 

 worked during ten hours out of every twelve, in a spring tide, for 

 vessels drawing 17 feet water. 



We shall give in Mr. Rendel's own words his plan of sluicing: — 



" It is proposed to run down daily any quantity of water between the 

 level of the tide of the day and that which may be considered best as the 

 permanent level of the water: so tliat, supposing the water were retained at 

 a permanent level of thirteen feet above the old dock datum, ihe average 

 high-water of spring tiiles being IS ft. 3 in. above that level, there would 

 be 5 ft. 3 in., the difference between the permanent level and the tide of the 

 day. The running off the water is a very important feature in the plan: 

 the idea is to make sluices, or apertures, under the great gates and the tide- 

 gates, passing out near the level of the bottom of the great basin, ami con- 

 sequently under the whole of the gates. The openings for the discharge of 

 the water will be between the bottom of the basin and the level of the sills of 

 the tide-gates and of the locks, as low as we can conveniently get them ; say 

 for argument sake, ten feet below the level of low water of average spring 

 tides. The sluices will be so formed as to be five feet square at tlie top on 

 the inside, and they will be gradually widened in horizontal dimensions, so 

 as to produce a kind of sheet of water within two feet of the bottom of 

 the great basin, and inasmuch as the separating piers of those apertures 

 will only be at the point of outfall about two feet thick, the effect will be 

 to have one wide sheet of water of the width of the basin ; the consequence 

 of that is, that we shall be able to operate upon the bottom of the basin, not 

 in the usual way of a large bore of water tearing up everything before it, 

 but a sheet of water which we can regulate to any degree of force which 

 we like, by the sluices on the inside. I should also say further, that we 

 have the sluices there, because they will operate most efficiently upon the 

 straight part of the basin ; we propose to have the same kind of sluices be- 

 tween the little dock which we have called the Bridge End Dock, and 

 the arm of the basin running up to it, operating in the same way precisely. 

 I wish it to be distinctly understood, that we do not propose to run those 

 sluices in the ordinary way of sluicing. I want to give the water, which is 

 to be discharged out of this great basin, more the effect of a river passing 

 through with a gentle current, than a great body of rushing water, and I 

 arrange the sluices with this view. It is also manifest that a basin of such 

 capacity as this basin, will have lying in it a number of vessels, say of from 

 six to ten feet draught of water ; those very vessels will be the means, with 

 a gentle current, of keeping the basin clear with the daily operations we 

 shall employ in running off this water. 



If the basin were unoccupied the effect would not be so great as it will 

 be the basin beinj^ occupied. If the l>asin were formed at the level of low 

 water, or if it were not occupied, the effect of the sluicing would not be so 

 great as it will be from the fact that vessels are floating in the basin, whe- 

 ther in large quantities, or small ; if the quantity of vessels is small, I 

 would then give the water a greater current ; if it is large, I would then 

 give it a gentler current, so that we can command that kind of current 

 passing under those vessels from their being afloat, which wUl keep the 

 Ijottom clear of the daily accretions. 



Also we can run off the water at those periods that experience will dictate 

 to be the best. We are not bound to run it off at low water, or any par- 

 ticular period of the tide : that would be regulated by a regard to all the 

 circumstances of the case. 



I know from considerable experience, that many harbours are kept open 

 entirely by the vessels lying in those harbours ; the river is forced to pass 

 under their bottoms, and in that way the water is kept at a proper depth. 

 I believe that is notorious." 



There will be the power of running off 1,600,000 cubic yards 

 of water at spring tides, which will be available for scouring. The 

 most available water for scouring now passing out of Wallasey 

 Pool is 1,390,000 cubic yards; that is to say, the water passing off 

 after half-tide. 



Mr. Rendel's estimate is, for cofferdams and other temporary 

 works, £15,323 ; excavations, j£80,4.70; masonry, £198,513 ; gates 

 and bridges, £21,268 ; draining, £22,572; land and contingencies, 

 £53,379. Total, £391,908. 



The peculiarity of Mr. Rendel's plan is the damming- up of the 

 upjier Pool, so as to make a float. Messrs. Mawdesley and Smith 

 had proposed simply to deepen and wall the Pool, wliieh was sup- 

 ported by some of the opposition parties. Mr. Rendel affirmed 

 that this would do no good, but leave the Pool even more liable to fill 

 up, as it would receive the water at an earlier time of the tids, 

 when charged with a larger quantity of matter. 



Mr. Rendel's researches on the tidal actions of the Mersey 



