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THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[JUN] 



great object to be kept in view in carrying into effect the improve- 

 ment of the navigation of tlie Liine, is the free admission of the great- 

 est possible quantity of water from the sea." Conformably to this 

 decisive conclusion, "The reporters beg leave particularly to point 

 out the necessity of using much caution in encroacliing on the tide- 

 covered banks of the river, and the shutting out large portions of the 

 tide Wilier, and impeding tlie effect of that powerful, constant, and 

 therefore most efficient of all agents in preserving the depth of navi- 

 gable channels." 



Directly opposed to this imperative conclusion, I should think that 

 reliance ought to be chiefly placed upon the scuur which the fresh 

 water and tidal wave combined occasion in a fixed and compressed 

 channel, because their united action and force is concentrated and con- 

 stant; whereas, in a widely spread estuary, their action is trivial on 

 any given line of channel, liable to cliange and to obstruct navigation. 

 Hence a perfectly even, a compressed, and a securely fixed channel is 

 that by which the navigation of tlie Lune may be the most effectually 

 improve<l ; and not by placing reliance on the scour effected by the 

 tide cliiefly, as Messrs. .Stevenson would appear to intimate. 



Agreeably to my view of the effect produced by the combined scour 

 of tidal and fresh water in a compressed channel, is not silt frequently 

 deposited along the quay of Lancaster by the tides in summer, winch 

 autumnal and winter floods of fresh water scour off again ? This is so 

 far an undeniable fact, and utterly at variance with the absolute theory 

 put forth by Messrs. Stevenson. Let the fresh water stream be alto- 

 gether withdrawn from the channel of the Lune, and in a very few 

 years that channel might be confidently expected to become superior 

 marsh land. Because the tidal force at its greatest power, according 

 to the elaborate survey of Messrs. Stevenson themselves, during the 

 flux of spring tides in the Lune, exceeds that of the reflux tides more 

 than two fold ; and hence more silt is driven upwards by such tides 

 (" the most efficient of all agents in preserving the depth of navigable 

 channels," as Messrs. Stevenson assert,) than the power of their reflux 

 is adequate to carry back to the sea again. In so far all the facts col- 

 lected by these engineers themselves, are utterly at variance with a 

 theory on tidal agency, they have expressed in the most unqualified 

 terms. 



When they reported in such a manner on the navigable channel of 

 the Lune, did they forgot that of the Clyde for fifteen miles below 

 Glasgow ? or have they witnessed the channel of the Tyne from New- 

 castle to Tynemouth ? or that of the Avon from Bristol to King's 

 Road ? And are they unacquainted with the fact that the channel of 

 the Thames, fixed in a compressed course by the strong ground of 

 Tilbury on the north and Gravesend on the south, is navigable for 

 steam boats, at all times of the tide, for seventy miles from the sea? 

 These undeniable instances of compressed channels of navigation, may 

 well be left to stand in evidence of themselves. Nor can I believe 

 that a navigable funnel so perfectly true throughout, and splendid in 

 outline as tlie Thames is, can have been otherwise formed than by the 

 unerring science of a day gone by. 



What have we on the opposite side of the account? The wide- 

 spread estuary of Morecambe Bay, where there is water enough from 

 the sea, combined with fresh water streams of great power. Then the 

 Duddon claims our notice ; and the Ribble also; — not to mention the 

 Lune itself. The wash of Lincolnshire is another instance ; and so is 

 the Solway Firth. Now all these navigations are confessedly bad ; 

 and unimproveable except by compression. Then they might some of 

 them riral the navigation of the Thames, the Tyne, the Avon, or the 

 Clyde. In Kirkbrule Loch, the channel of the Wampool, in five miles 

 from the Solway Firth, loses about 15 feet of fall ; it then assumes an 

 exceedingly comjiressed form, and though but a trivial stream, it then 

 maintains a dead level for three miles inland, along which high spring 

 tides flow. .Such a mass of strong evidence needs no comment. 



Indeed, with a body of evidence before us so conclusive, why does 

 the channel of the Lune undergo a diminution in depth of water from 

 Heaton to Lancaster at all ? The facts collected by Messrs. Stevenson 

 answer this question satisfactorily. For a short distance below the 

 quay of Lancaster the bed of the channel is found to be composed of 

 three feet of hard gravel, resting upon fluviatile clay, or more properly 

 speaking — compressed si!t deposited by the flux tides of the sea. It 

 is obvious that the crust of gravel which now forms the bed of the 

 channel, has been brought down the course of the Lune by a succession 

 of floods from the uplaTi<l>, and deposited on those levels, which the 

 combineil reflux of tides and fresh water floods have not had power 

 enough to scour out to sea. Yet on even these unequal terms, the loss 

 of fall from Lancaster to Heaton is about 2G per cent, loss per mile 

 than from Heaton to Glasson. Had the tidal scour, therefore, on that 

 portion of the channel where the admission of water from the sea is 

 the greatest, and r.otv.ithslanding an accumulation of gravel from the 

 Uplands, been equal to what it is where the tideway is the most com- 



pressed, the actual depth of water at Lancaster quay must have been 

 three feet more than it is at present. With a Ittidy of facts and inci- 

 dents so plainly in the possession of Messrs. Sicvenson, for what rea- 

 sons, or on what authority they adopted the theory of — "The free ad- 

 mission of the greatest possible quantity of water from the sea," I 

 shall leave to their candid explanation ; and I think myself abundantly 

 justified in tearing away the entire foundation of a theory so fallacious 

 and opposed to the improvement of navigable channels in general. 



When all the evidences under which the port of Lancaster may be 

 placed are brought into a distinct sum, the whole matter for considera- 

 tion is plainly brought before the commissioners of the port, and awaits 

 their decision. Shall the accumulation of gravel from the Uplands be 

 allowed to continue until Lancaster ceases to be a port? Certainly 

 not. The value of the quay and warehouses alone, not to say the 

 prosperity of the town, and the traffic of its railway, demand the most 

 spirited and well considered exertion, though the task left for their 

 execution may be an arduous one. 



Foremost in importance is the removal of gravel and silt from the 

 channel of the Lune between the old bridge and Oxcliffe. Under skil- 

 ful modes of carrying on the work, I should think that it might be 

 accomplished for lid. per cubic yard, as most of it could be stowed 

 away at an easy distance. Dredging, including every expense, as 

 estimated by Messrs. Stevenson, and taking into account penetrating 

 an extended bed of hard gravel, may be fairly taken at Is. Sd. per 

 cubic yard. This so far decides in favour of the barrow, the pickaxe, 

 and spade. Suppose then a removal of 240,OOU cubic yards, at Grf. 

 per yard, this head of expenditure would be G,OUOi. In addition to 

 this, a portion of dredging would be called for on ground where the 

 working of the machinery was less hazardous and severe than upon 

 hard beds of gravel. Admitting, therefore, that &U,OUU cubic yards 

 could be removed by contract at Is. per cubic yard, the charge thereon 

 would be 4,00U/. ; thus giving a total charge of 10,UU0/. In addition 

 to these operations, were every facility given for the reclamation of 

 land by silting it over within the channel of the Lune, 4,U00 acres so 

 reclaimed, at a deposition of 10,0U0 cubic yards per acre, would ab- 

 sorb 40,0U0,000 cubic yards on the whole, fix a secure channel, and 

 give a depth of water at Lancaster quay surpassing the highest ex- 

 pectations, thus giving an impulse to the commercial activity of the 

 town, and tlie prosperity of its manufactures. 



jSkehiod, IVigton, Cumherland, 

 Ftbruary 6, 1830. 



Sir — Yesterday a gentleman placed in my hands Mr. Brooks' work 

 on Rivers, Harbours, &c., and directed my particular attention to his 

 " New Tlieorv of the existence of Bars," among quotations of opinion 

 on this most important subject, there appears one from a letter of 

 mine which appeared some time back in the " Nautical Magazine," 

 and which Mr. Brooks states are "the words of one who has devoted 

 much time to the promulgation of his theory," c. g. "that egress 

 sluicing, or scouring water is the sole cause of a bar ;" that he is quite 

 correct in this remark, your own columns bear testimony, and the re- 

 cords of parliament will also convey to posterity the fact that I first 

 published to the world this novel thesis, and the equally novel princi- 

 ple of forming Harbours of Refuge with double entrances, without the 

 use of back-water, a principle which is now recommended by the 

 Commissioners in their Report of a Survey of the Harbours on the 

 South East Coast, and for the same object, and in the same words, that 

 I have used in reference to this aft'air, viz. "to afford to vessels a free 

 ingress and egress, under all circumstances of the wind and weather." 



Taking a deep interest in a matter of so much importance to this 

 great naval and nautical nation, and numbering as I do among converts 

 to my thesis, some of the most eminent scientific and practical meu of 

 the day, I beg you will be pleased to reserve forme in your next num- 

 ber, a space for the insertion of some observations on Mr. Brooks' 

 Theory of Bars, as developed in the panq)hlet referred to, in which 

 obseivations I shall repeat my oft assertion "that bars are the ettects 

 of general, and not of partial laws, and that the bar at the entrance of 

 Bow-creek, in the river Thames, results from the same cause as do the 

 bars at the disemboguing of rivers in the Torres Straits, and on every 

 other coast in the world." I state this from observations of more than 

 20 years made on harbours and bars in various parts of Europe, and in 

 Africa. 



I remain, your's, &;c. 



HiiXRY Barrett. 



London, May 25, 1841. 



