The Crapponne Canal.—The authority to construct this canal was conceded to Adam de Crapponne, an eminent engineer in the year 1554. It takes its water through sluices, from the river Durance, near St. Estève-Ianson, at an altitude of 492 feet above sea level. There the river varies from 600 to 6500 feet in width, and the bed consists of a succession of sand and gravel banks, and alluvial deposits, intersected by numerous branches, which shift at every flood. Such a state of things cannot be considered as constituting the bed of the river, in the ordinary acceptation of the term, and to have constructed a permanent and fixed barrage across the river, to lead the water through the sluices, would not only have been a costly work at that time, but also one of considerable difficulty. Crapponne constructed, therefore, what are termed “barrages volants” across the river. These are formed where the depth of the water is about two feet, by stakes with fascines, and filled in with stones. In the deeper parts of the river, which may be sometimes 12 to 15 feet, “chevalets” are driven in place of stakes. These consist generally of trunks of trees cut near the point of the bifurcation of the principal branches, and which are placed closer together in proportion to the depth. The “chevalets” are bound by cross-pieces and supported by fascines. These “barrages volants” are always placed obliquely to the current of the river, for the purpose of causing the fascines to press against the stones or the “chevalets.” Such “barrages volants” need continual repair, but their cost is comparatively trifling. It is mostly a question of labour, as the material employed is cheap.
The average cost of maintenance of the barrage for the Crapponne canal is about 500l. per annum. This system, adopted by Crapponne more than 300 years ago, has never been changed, and has been found by experience to answer its purpose of diverting the Durance waters through the sluices into the canal in all seasons, and the same system is adopted for some other irrigation canals. The Crapponne Canal, is the main canal from the river Durance to Lamanon, and is 14¼ miles in length. At Lamanon the canal has two main branches, one flowing south towards Salon and St Chanas, and the other to the west towards Arles. The total length of the canal is about 77 miles, not comprising the whole development of the branch to Arles, which is a special property, independent of the original canal.
The quantity of water supplied by the canal, is as follows:-The main canal is 26 feet wide, and 6·5 feet deep; the mean velocity is 5 feet per second. The branch to Salon is 10 feet wide, and 6·5 feet deep; the mean velocity is 6·5 feet per second. The branch to Arles is 16·5 feet wide, and 3·28 feet deep; the mean velocity is 5·3 feet per second. The branch to Istres is 6·6 feet wide, and 3·3 feet deep; the mean velocity is 6·6 feet per second.
The Alpines Canal.—This canal, which was commenced in 1773, takes its water, for the main channel, from the Durance at Mallemort, and for the west branches, near Chateaurenard. The main canal is considered one of the best in Europe as regards its utility. The system consists of more than 194 miles of canal, disposing of 770 cubic feet of water per second, which, with the west branches of the canal, irrigates more than 20,000 acres. The branches to Carascon and Barbentane, have generally an inclination of 1 in 2000. In some portions of the former branch, the inclination is 1 in 4500; in other portions 1 in 1250, while over some of the aqueducts it is as much as 1 in 154. The widths at the bottom of the west branch canal vary from 7·8 to 9·2 feet, and for a branch to Barbentane, between 5·2 and 6·2 feet. The inclinations of the slopes varies from 1 to 1, to 1½ to 1, in ordinary cuttings and embankments. The west branches of the canal have passed through considerable financial difficulties, and are now managed by an independent company.
In order to develop irrigation, numerous syndicates have been formed, as some of the land was held in small parcels by proprietors and farmers who had neither the funds nor the power, in opposition to intervening landowners, to obtain branches to conduct the water from the main irrigating canal to their properties. The price charged for the water is regulated by the price charged for corn on the basis of 1·66 bushel per acre irrigated. The quantity of water given at the above rate, is fixed about 0·57 gallon per acre per second, supposed to flow continuously during the irrigation season, commencing on the 1st of April and terminating on the 1st October of each year, which is equal to covering the ground for the total number of irrigations to a depth of 66½ inches, and with 22,130 cubic yards of water. In 1874, the cost of irrigation was equivalent to about 11s. 6d. per acre, being the price of 1·66 bushel of corn. The price has recently been reduced to about 8s. per acre, for three irrigations required during the season for such crops as corn and olive orchards. The same reduced price per acre is also charged for inundating vineyards during the autumn, as a preventive to the phylloxera.
Lens la Deûle Canal.—Lens, a town of 11,800 inhabitants, and the capital of the coalfields of the Pas-de-Calais, has recently been connected with the existing system of navigable waterways by a canal, which passes near a great number of pits belonging to the companies of Lens and of Courriéres, the most important of the district, and serves the Liévin mines, which previously possessed no water communication. The probable traffic on this canal has been estimated at 290,000 tons, with a prospect of future increase. The canal starts a little beyond Lens, and passes close to the town; and after a course of 4 miles 7 furlongs it joins the Souchez Canal at Harnes. This canal, about 2 miles 1 furlong in length, was constructed about 1862, and connects the Lens Canal with the Deûle Canal a little beyond Courriéres. The total fall of the Lens Canal is 31 feet 10 inches, which is effected by three locks, the first by a fall of 8¼ feet and the other two of 11 feet 9½ inches. It has a bottom width of 17¾ feet in the straight portions, and in the curved portions the width at the bottom is regulated according to the formula (17¾ × 1246⁄R) feet; and its depth is 7¼ feet for an available draught of 6½ feet. Crossing places, 31 feet wide at the bottom and 360 feet long, have been formed about every 5 furlongs; and places for barges to wait in have been constructed of the same width, at the commencement and end of the canal, 2300 and 1800 feet long respectively. Above the third lock the canal traverses fissured chalk for a distance of 1640 feet, and has accordingly been lined with concrete up to 1 foot above the water level at a cost of 2l. per yard; and where the canal passes over a marsh, filled up with stones from the pits, for about 330 feet, it has been cut off from the marsh by a puddle-trench carried down into a substratum of clay 13¾ feet below the water-level. The locks are of the ordinary type, 17 feet wide, 126⅓ feet available length, and 8¼ feet in depth, with sluices in the gates; and the gates have iron ribs and a wooden skin, and cost on the average 4l. per square yard. The canal is fed by the river Souchez only 620 feet from its commencement. The discharge of the river during the long drought of the summer of 1886 did not fall below 4·6 cubic feet per second, whilst the traffic on the canal only required 2½ cubic feet per second, allowing for losses from evaporation and leakage. There is, therefore, an ample supply for other purposes, and for increased demands for traffic. The canal was begun on the 1st of February, 1885, and was opened for traffic on the 30th of October, 1886. The works, including land, cost 74,000l., or 15,206l. per mile.
The Marne Canal.—The original canal was constructed between the years 1838 and 1853. It commences by a junction with the Upper Marne Canal at Vitry le Français, and terminates by a junction with the river Ill and the Rhine Canal, near Strasburg, thus connecting the valleys of the Seine and the Rhine, and also the intervening rivers, which include the Maas, Moselle, Soar, &c. Its length between Vitry and Strasburg is 193½ miles, and it crosses the four watersheds dividing the catchment basins of the Marne, Maas, Moselle, Soar, and Rhine; there are, however, only two summit reaches, as the divides between the Maas and Moselle, and the Soar and the Rhine, are tunnelled through at Fory and Arzweiler, respectively. There are altogether five tunnels, with a total length of 5½ miles.
The level of the water above the sea is, at Vitry, 332·62 feet; at the Mauvages summit tunnel, through the Marne-Maas divide, 922·75 feet; at Nancy, 648·10 feet; at the Vosges summit level, 873·93 feet; and at Strasburg, 444·18 feet. There are 177 locks on the canal, and the mean rise of each is 8·60 feet.
Some years since it was contemplated to increase the water supply, but the improvements were delayed by the Franco-German war, which resulted in a transfer to Germany of the Alsatian portion of the canal, and also of one of the most important sources of supply, viz. the river Soar. To render the system independent of this latter portion, in 1874 the construction of the East Canal was authorised. This commences at Givet, on the Belgian frontier, joins the Rhine-Marne Canal at Troussey, and again leaving the latter canal at Toul, follows the course of the Upper Moselle to Epinal, where it branches off in a south-westerly direction to its termination at Port-sur-Saône. The depth of water in this canal was fixed at 6 feet 6 inches.
The Rhine-Marne Canal had originally a depth of 5 feet 3 inches, a bottom breadth of 32 feet 10 inches, and sides sloped at 1½ to 1. This depth has been increased to 6 feet 6 inches, the canal bed has been cleaned and lined with concrete 6½ inches to 8½ inches thick, where necessary, and the headways of the bridges and tunnels has been raised to 12 feet 2 inches above the new water-level. Through the Mauvages tunnel a chain has been laid, and all the traffic is worked by two chain steam-tugs with fireless boilers (Francq’s patent).