Page:Encyclopædia Britannica, Ninth Edition, v. 4.djvu/871

Rh CANAL 789 tions, and one pair in the centre. The northernmost side passage for barges is 30 feet long and 3 1 feet wide, with three pairs of gates ; that to the south is 227 feet in length and 40 feet wide, with five pairs of gates. FIG. 6. Plan of Locks on Amsterdam Canal. Tn constructing the canal,which is (187G) now far advanced towards completion, the cuttings were first begun. The material proceeding from these cuttings was deposited so as to form two banks 443 feet apart, through the lakes on each side of the main canal, as shown by the hard lines on the plan, and also to form the banks of the branch canals on either side. The total length of these banks is 38^ miles. The nucleus of the bank is formed of sand with a coating of clay, and protected during its progress with fascines ; and when the banks are far enough advanced, the deep channel for the canal is excavated by dredging. The cross section of the canal and banks through these meers or lakes is shown in fig. 7. The formation of the banks through the Wyker Meer and Lake Y will enable about 12,000 acres of the area, as shown on the plan, which is now occupied by these lakes, to be reclaimed. For the purpose of this reclamation, and also to provide for the drainage of the land on the margin of the lakes, including a large portion of what was formerly Haarlem Meer, pumps are provided by the company at various points on the main and branch canals. The Canal Company are bound to keep the surface-water of the canal about 1 foot 7 inches below average high-water level. In order to insure this level being maintained, three large pumps have been erected in connection with the locks hereafter to be described, on the dam between Amsterdam and the Zuider Zee. They consist of three Appold pumps, the largest of the kind yet made, the fans being 8 feet in diameter. Each pump is worked by a separate engine of 90 nominal horse-power. The maximum lift is 9 feet 9 inches, at which the three pumps are capable of discharging 1 950 tons a minute ; with the ordinary working lift of 3 -j- feet they will discharge 2700 tons a minute. - Lake Y extends about 4|- miles to the eastward of Amsterdam ; and here it was necessary to form a dam with locks for the passage of vessels. The dam crosses Lake Y at a point about 2 miles to the eastward of Amsterdam, where it is contracted to 42G5 feet in width. As it was necessary to construct these locks before completing the dam across Lake Y, a circular cofferdam 590 feet in diameter, consisting of two rows of piles 49 feet long, was constructed in the tideway, and within this dam the locks were built. Theso locks have three main passages, each with five pairs of gates, and one smaller passage with three pairs of gates, arranged much in the same manner as the North Sea locks in fig. G. The whole of the masonry and brickwork for these locks and sluiceways was founded on bearing-piles, upwards of 10,000 in number. The bottom where the cofferdam was placed consisted of mud, and some difficulty was experienced in maintaining it till the work was completed. The dam across Lake Y, as shown in section, fig. 8, consists of clay and sand, placed on and FIG. 8. Section of Dam across Lake Y. protected at the sides by large masses of wicker-work, which is afterwards covered with basalt in the manner usually adopted in Holland. All the lock gates at both ends of the canal pointing seawards are of malleable iron; the gates pointing in wards towards the canal are of wood. The necessity, for drainage purposes, of maintaining the surface water of the canal at the prescribed low level calls for a suffi cient barrier being provided against the sea at both ends, as the sea-level will not unfrequently, at high water, be several feet above the level of the canal. This necessity, as well as the difference of level and periods of high water in the Zuider Zee and the North Sea, required a totally different design from the Suez Canal, to be afterwards described. The contract sum for the execution of the Amsterdam Canal is 2,250,000, and it is expected that it will be iv.ady for traffic in 1877. Of the third class of works there is, as yet, only a single Suez Canal, example in the Suez Canal, one of the most remarkable engineering works of modern times ; but though it is called a canal, it bears little resemblance to the works we have described under that name, for it has neither locks, gates, reservoirs, or pumping-engines, nor has it, indeed, anything in common with canals, except that it affords a short route for sea-borne ships. It is in fact, correctly speaking, an artificial strait or arm of the sea, connecting the Medi terranean and the Bed Sea, from both of which it derives its water-supply ; and the fact that the two seas are nearly on the same level, and the rise of tide very small, allowed this construction to be adopted. The idea of forming this connecting link between sea and sea is of A r ery ancient origin, and its author is unknown. It is understood, however, that a water communication for small vessels between the two seas was formed as early as GOO years before the Christian era, and existed for a period of about 1400 years, after which it was allowed to fall into disuse. Baron De Tott in his Memoirs of the Turks and Tartars, 1 written in 1785, after giving quotations from the historian Diodorus as to the existence of certain portions of the early work, and its having been abandoned in consequence of the supposed difference of level between the two seas, and threatened inundation of Egypt, says there still exist those early traces of work &quot;qu unleger travail rendrait ^navigable sans y employer d ocluses et sans menacer 1 Egypte d inondations.&quot; De Tot t s opinion expressed in 1785 has certainly been carried out, but on a scale and at an expenditure of labour and money far beyond the conception of the French diplomatist. The idea of restoring this ancient communication on a 1 Memo-ires du Baron de Tott, sur les Tares ct Ics Tartarcs, Amster dam, 1785, vol. ii. p. 271.