The Act provides that the Bridgwater Navigation Company shall sell the whole of the Bridgwater undertakings for the sum of 1,710,000l.
These undertakings earn a net revenue of nearly 60,000l. per annum.
Under the auspices of the Manchester Ship Canal Company, a considerable development of the traffic on the Bridgwater canal system is expected to result from the abolition of the bar tolls, which obstruct traffic, and from throwing open the canal to general carriers.
Description of the Canal Works.
A brief description of the canal works may here be introduced. The engineering journals, from which we have mainly borrowed our facts, have dealt with them so fully as to render a detailed statement quite unnecessary.
The Manchester Ship Canal begins at Eastham, on the south bank of the Estuary of the Mersey, and about midway between its mouth and head near Runcorn. The canal follows this bank for 13½ miles, the greater portion being in entirely solid ground, but, sometimes going below high-water mark, it is confined by embankments and retaining walls until reaching Runcorn, where it leaves the waters of the Mersey, and takes an independent and almost direct course to its terminus in the docks at Salford and Manchester.
The total length of the canal is slightly over 35½ miles. This is practically one continuous cutting, but it has been subdivided into thirty lengths or sections, each with a local name and number; these vary in cubical contents from 223,000 cubic yards in the smallest, to 3,345,000 cubic yards in the largest. The total quantity of earthwork to be moved is 44,428,535 cubic yards, composed of 6,970,815 cubic yards of rock, and 37,457,720 cubic yards of soft materials. Of the rock, 1,591,570 cubic yards will be utilised for lock and river wall work, abutments of railway bridges, facing slopes of the canal in soft ground, and other operations, the remainder going to spoil. Of the soft excavations 3,603,690 cubic yards are to be used in forming the embankments of the canal, 5,176,278 cubic yards for forming embankments on railway diversions, 1,555,000 cubic yards in filling up what will be the disused bed of the Irwell and other water-courses; 552,000 cubic yards in raising quays and making roads; 800,000 cubic yards are to be stacked along the canal banks for future use in maintenance; and the remainder, amounting to 31,149,997 cubic yards, will go to spoil.
The carrying of the Bridgwater Navigation across the Manchester Canal at the distance of 32 miles, will be one of the most interesting works in the contract, because an entirely new departure will be undertaken in the aqueduct. It was on this navigation that Brindley made his famous viaduct, the precursor of the more splendid structures of Rennie and Telford.
As the level of the Bridgwater Navigation has to be maintained, and as the saving of water is a consideration, Mr. Williams proposes to make the aqueduct in the form of a swing bridge, which may be opened, swung, and closed again without losing any water either from the swinging portion or from the canal. Here also, parallel to the aqueduct, will be constructed a hydraulic lift, to lower barges and boats from the waters of the navigation, to the canal, where they will cross on its level to a similar lift, there to be raised to their former waters and level. A similar lift has been at work for some years with satisfactory results at Anderton on the Weaver Navigation, of which Mr. Leader Williams was formerly the engineer.
Throughout the entire length of the canal, hard red sandstone forms the bedrock, and the formation, of course, varies according to the nature of the stratification. For instance, at 1½ miles distance, where the canal works are inside high-water mark, all layers of deposit have been washed away, and only from 2 feet to 4 feet of black sludge overlies the rock. Occasionally the rock dips and leaves the bottom of the canal in the softer deposits, in some places beds of what has been termed black river sludges, but which are, in all probability, peaty deposits, are sandwiched in, and underlie deposits of from 15 feet to 16 feet of clean river sand. At 5½ miles between Stanlow Point and Ince Lighthouse, large beds of blue loam are met with, varying in depth to 25 feet; and at 6 miles black sludge comes in again, about 20 feet in thickness. At 6½ miles there is a peculiar erosion of the underlying sandstone, apparently from some creek having cut across the line of canal. At 8 miles the section overlies a bed of gravel, and at 9 miles the bottom of the canal runs into a large deposit of sand. From about 10 to 10½ miles the strata becomes very soft, being sludge, sand, and gravel mixed. At 11 miles 45 chains the bottom of the canal is again very soft ground, the sandstone suddenly dipping and not appearing again until about 12 miles.