Waterways and Water Transport in Different Countries / With a description of the Panama, Suez, Manchester, Nicaraguan, and other canals.

by J. Stephen Jeans

The embankments formed across the low grounds on either side of the Barton viaduct were considered very formidable works at that day. A contemporary writer speaks of the embankment across Stretford meadows as “an amazing bank of earth, 900 yards long, 112 feet in breadth across the base, 24 feet at the top, and 17 feet high.” The greatest difficulty anticipated was the holding of so large a body of water within a hollow channel formed of soft materials. It was supposed at first that the water would soak through the bank, which its weight would soon burst, and wash away all before it. But Brindley, in the course of his experience, had learnt something of the powers of clay puddle to resist the passage of water, and he finished the bed of this canal, so as to make it impervious to water.

Not the least difficult part of this undertaking was the formation of the canal across Trafford Moss, where the weight of the embankment pressed down and “blew up” the soft oozy stuff on either side; but the difficulty was again overcome by clay puddle. Indeed, the execution of these embankments by Brindley was regarded at that time as something quite as extraordinary in their way as the erection of the Barton Aqueduct itself.

Embankments and Weirs.

Mr. Jebb has pointed out[283] that one of the most important duties of the canal engineer, and certainly one of the most anxious, is to take all practicable precautions for the prevention of any of the embankments giving way by the overflow of water during heavy rainfalls.

In some districts at such times an enormous volume of water discharges directly into the canal; this has to be got rid of. Self-acting weirs are constructed at convenient points, and these are sufficient to keep the water within bounds at ordinary times; but in times of flood other means have to be used. The old canal “let-off,” as it was called, consisted of a wooden frame (fixed in the bed of the canal), to which was attached a hinged lid; this lid was pulled up by a chain fixed to the lid when necessity required—that is, if the chain could be found, and also sufficient power obtained for the purpose; for when the let-off had not been used for a considerable time it became covered with mud, and it was often as much as half-a-dozen men or a horse could do to pull up; this accomplished, however, the water rushed out at once with great force (as there was no means of regulating the discharge), the sudden rush often causing trouble with the owners and occupiers of the adjoining lands. Mr. Jebb has replaced some scores of these let-offs by sluice valves of similar capacity, worked by racks and pinions. The discharge of water can thus be exactly regulated, and one man only is required to work them. The valves are tested every month to see that they are in working order.

For the proper and economical maintenance of the towing paths, it is necessary to have a staff of experienced men. Mr. Jebb recommends, as a material for metalling, limestone débris, or what is locally known in Birmingham as “raffil” or “bavin.” He finds that it sets soon, and lasts for years if properly laid down—broken furnace cinders, covered with good ashes, are largely used in the Black Country—the paths should, of course, be well drained.

On the Birmingham canal, between Longford and Manchester, the sidelong ground was cut down on the upper side and embanked upon the other by means of the excavated earth. This was comparatively easy work; but a matter of greater difficulty was to accommodate the streams which flowed across the course of the canal. For instance, a stream called Cornbrook was found too high to pass under the canal at its natural level. Accordingly Brindley contrived a weir, over which the stream fell into a large basin, from whence it flowed into a small one, open at the bottom. From this point a culvert, constructed under the bed of the canal, carried the waters across to a well, situated on its further side, where the waters, rising up to their natural level, again flowed away in their proper channel. A similar expedient was adopted at the Manchester terminus of the canal, at the point at which it joins the waters of the Medlock. It was a principle of Brindley’s never to permit the waters of any river or brook to intermix with those of the canal, except for the purpose of supply; as it was clear that in a time of flood such intermingling would be a source of great danger to the navigation. In order, therefore, to provide for the free passage of the Medlock, without causing a rush into the canal, a weir was contrived, 306 yards in circumference, over which its waters flowed into a lower level, and thence to a well several yards in depth, down which the whole river fell. It was received at the bottom in a subterranean passage, by which it passed into the river Irwell, close at hand.

In the earlier attempts made in the last century to deal with the cataract of Trolhätta, in Sweden, it was determined to distribute the whole fall of 113⅓ feet among three sluices only: the first to consist of 28, the second of 52, and the third of 33⅓ feet. These sluices were to be constructed alongside of the three cataracts, and were to be each 18 feet wide by 72 in length. The work advanced successfully, until the attempt to throw a weir across the river at the gulf of the last cataract, to raise and retain the water above it. The impetuosity with which the whole stream is precipitated had prevented the builders from sufficiently examining the bottom. They had conjectured, from the nature of the neighbouring mountains, that the bottom must be rock; and it was further supposed that there could not be more than 10 feet of water. Both these suppositions proved to be erroneous. The depth of the water was from 20 to 25 feet at least, and the bottom was composed of large detached stones, which were incapable of being fixed by any efforts of art. The caissons of stone, although fastened together with cramps 4 inches thick, and attached by great piles to the mountains on both flanks, were swept off and dispersed by the impetuosity of the current; and in this manner all the works were destroyed.

Subsequently it was determined to avoid the pass entirely, and construct a canal 8200 feet long; and the total fall of 113⅓ feet was to be distributed, in the space of the last 3000 feet, among seven sluices or locks, each 36 feet in breadth by 200 in length.

The first sluice was to be 17⅓ feet in height; the others, 16 feet. The first sluice was to stand alone; but the four following were to be close to each other, as were also the last two. Between the fifth and sixth sluice the canal was to be protected by a strong dyke against the floods of the river. There was to be a great discharger between the first sluice and the water entrance, not far from the centre; and at the entrance itself two doors or gates, to lay the canal dry when required. This plan proved more successful than the first.