lOO 



NATURE 



\Nov. 30, 187^ 



trustees, and upwards of 200 jetties were thrown out 

 between Glasgow Bridge and Bowling-, a distance of 

 eleven miles. During the next forty years improvements 

 continued to be carried on, and the names of Telford and 

 Rennie appear again in connection with them. In 1836 

 a report of Mr. Walker, the engineer to the navigation at 

 that time, showed that there was a depth of water at the 

 Broomielaw, just below Glasgow Bridge, of 8 feet at 

 low water, and he adds that " the river which bv artificial 

 means was to be rendered capable of taking craft of thirty 

 to forty tons to Glasgow, has, by what Golborne called 

 * assisting Nature,' been rendered capable of floating 

 vessels nearly ten times the burthen," But improvement 

 did not stop here. Since that date the Harbour of Glasgow 

 has been widened by 240 feet, and vessels of 3,000 tons 

 burthen can float where at that time stood one of the 

 largest cotton mills in the city. 



Some very curious phenomena connected with the 

 tides have resulted from the alterations of the tidal 

 channel produced by these engineering operations. The 

 level of low water in Glasgow Harbour has been getting 

 lower and lower, until it is now no less than 8 feet 

 lower than it was in 1758, and during the last fourteen 

 years there has been a depression of level of over a foot. 

 This has been accompanied during the same period by a 

 corresponding rise in the level of high water at ordinary 

 spring tides. These phenomena are no doubt due to the 

 greater facility with which the tidal wave can pass up 

 and down the river than formerly, its shallow, broken, 

 irregular, and tortuous channel having been straightened 

 and deepened, and obstructions offering resistance to its 

 flow having been removed. The increase of the rapidity 

 of the flow is as remarkable as the increase of the volume 

 of water. In the year 1807 the time of high water was 

 three hours later at Glasgow than at Greenock, thirty 

 years after there was a difference of i hour 23 minutes, 

 and at the present time that difference has been reduced 

 to I hour and 5 minutes. At Greenock the tide flows for 

 about 6j hours and ebbs for about 6 hours, whereas at 

 Glasgow it flows for 5I hours and ebbs for 6| hours. 



In the improvements of the Clyde the one principle 

 followed by all the engineers has been the increasing of 

 the volume of the tidal wave and the prolonging of its 

 flow into the upper reaches of the river. Very little work 

 has been done by the natural fresh-water stream, although 

 that is estimated at an average of 48,000 cubic feet per 

 minute, which represents in round numbers over 300 

 million gallons for every twenty-four hours. This fact 

 demonstrates very forcibly that it is to the tidal ebb and 

 flow that we must look for the conservation of the chan- 

 nels of tidal rivers, rather than to the action of the land- 

 water, which cannot be depended upon for constancy, and 

 its tendency is more often to deposit than to scour. 



To keep the channel of the Clyde in order, constant 

 dredging all the year round has to be maintained, and 

 under the able administration of the engineer to the 

 navigation this has been brought to a high state of per- 

 fection, both in amount of work done and in its very 

 small cost, averaging as it does from about one shilling 

 per cubic yard for gravel to i\d. per cubic yard for sand, 

 and these costs are inclusive of repairs. 



Although the Trustees already possess the largest 

 steam-dredging fleet in the world, they have lately 

 given to Messrs. Rait and Lindsay, of Glasgow, whose 

 firm has a world-wide reputation for the construction of 

 such plant, an order for four new steam hopper barges, 

 thus Ijringing the number up to eighteen. These vessels 

 are designed by Mr. Deas, and will measure 150 feet 

 long, 26 feet wide, and 12 feet deep, and each capable of 

 carrying 500 tons of dredged material. They will be fitted 

 with compound high and low pressure engines, which will 

 also be constructed by Messrs. Rait and Lindsay. 



Dredging is employed for widening the river as well as 

 for deepening the bed. When a bank has to be cut away 



the dredger is worked close to it so as to undermine it 

 and by this means much cost of excavation is saved. 



For the removal of boulders, some of which weigh ovei 

 six tons, diving bells are employed. Last year one bel 

 lifted no less than 656 tons of boulders from the bed of th( 

 river. These bells are alsoemployed for removingthe/f<?i5;7. 

 resulting from sub-aqueous blasting operations which an 

 continually going on, both dynamite and gunpowdei 

 being employed for the removal of Whinstone or trar 

 rock. The charges are contained in tin canisters, whicl 

 are inserted in holes of 3 inches diameter drilled in the rock 

 which are afterwards sealed up with Portland cement 

 They are fired in groups by a voltaic battery on the decl 

 of the diving-bell barge, and the shattered rock is re 

 moved by the bells. 



To give an idea of the benefits which engineerin] 

 operations of this kind can confer upon the community 

 it is interesting to notice that whereas the reports 

 Smeaton, Telford, and Rennie, showed that the river wa 

 navigable only for barges to Glasgow, at the presen 

 time the registered export and import tonnage of Glas 

 gow amounts to 2\ million tons, or equal to half the ton 

 nage of London or of Liverpool. Population statistic 

 point to the same result. In 1831 the population of Glas 

 gow numbered 202,000, in 1861 it had risen to 395,00c 

 and it is estimated at the present time at 535,000. 



The great increase of the shipping trading into th 

 Port of Glasgow has had to be met by the extension 

 quays and by the construction of docks. The first c 

 these, Kingston Dock, was ojened in 1867, giving abou 

 5I acres of water-space, but the Trustees are now con 

 structing docks at Stobcross which will have an area 

 over thirty-three acres, and capable of accommodatinj 

 1,000,000 tons of shipping. A graving dock 560 fee 

 long and 72 feet wide, with a depth of water of 22 feel 

 has also lately been opened. 



The Stobcross Docks possess an especial scientifii 

 interest from the fact that the quay walls are supportei 

 on groups of concrete cylinders, a system of sub-aqueou 

 foundation adopted here for the first time by the Clyd 

 Trustees at the recommendation of Mr. J. F. Batemai 

 and Mr. James Deas, and the results have proved s 

 eminently successful that this system is likely to be uni 

 versally employed for dock foundations in sandy 

 gravelly soils. During the execution of this work th 

 variety of the geological strata was particularly interest 

 ing, ranging as it did from boulder clay of the mos 

 tenacious character to the finest and sharpest of sand 

 much of which was used for the manufacture of glass. 



The concrete cylinders are arranged in groups of thre 

 together, and are built up of rings formed in movabl 

 wooden moulds \ they are 27 feet 6 inches in heighi 

 made up of eleven rings each, and rest upon iron shoe; 

 When a group of three cylinders is built up to its heighi 

 diggers specially designed for the purpose are set t 

 work excavating the sand and gravel from within th 

 cylinders ; as this comes away the whole structure dis 

 appears into the ground, being helped in its descent b 

 the addition of about 300 tons of cast-iron weight 

 placed on the top. The average rate of sinking is abou 

 I foot per hour, but as much as 5 feet per hour has occa 

 sionally been attained. When the group has been sunk it i 

 cleaned out by the diggers to the level of the shoe, eac 

 cylinder is then filled with Portland cement concrete 

 and upon this foundation the quay wall is built. 



Want of space will not allow us to describe the hj 

 draulic swing bridge which will cross the entranc 

 from the river, nor to do more than mention the powerfu 

 hydraulic cranes built upon a similar foundation to that c 

 the quays. For these and many other particulars of grea 

 interest in connection with the River Clyde we must refe 

 our readers to Mr. Deas's book and to his paper " On th 

 Construction of the Stobcross Docks," read before Sec 

 tion G of the British Association, 



