Water Supply of Paris, France
The question of improving the water supply of this city was the subject of minute and careful investigations, extending over a period of four or five years (from 1854 to 1859).
Many projects were submitted to the Prefecture of the Seine, but the one finally adopted was that studied by Mr. Belgrand and the engineers of the municipality of Paris. The scheme consisted in appropriating the waters of the Sonne and the soude, together with the Soudon and the Dhuis, all being tributaries of the Marne, and flowing through chalk districts.
The population of Paris, for the supply of which the scheme was laid out, was taken at 2,000,000, and the waters from the sources selected were intended for the domestic supply only the existing supplies to Paris, which have become gradually polluted and unfit for domestic use, being made available for all the other general wants of the population. The quantity of water which it was estimated would be required for the domestic purposes of such a population was taken at 100,000 cubic metres per diem, or about 22,000,000 gallons per day; and the works have been laid out for conveying this quantity. Gaugings of the various streams selected, showed that in 1855, when the flow was at the lowest, the produce of the Sonne and the Soude was 1081 litres per second, the Soudon 100, the Dhuis 315, making a total of 1496 litres per second, or about 28,000,000 gallons per day. At the time of lowest water in 1857, however, the Sonne and the Soude together only yielded 880 litres per second, or 16,762,000 gallons per day, while in 1858, which was an exceptionally dry year (indeed the direst year on record in this locality), they yielded together only 285 litres per second, or 5,417,280 gallons per day; while in both these years the Soudon and the Dhuis have almost the same quantities as in the year 1855.
In order to meet the contingency of such a dry season as 1858, Mr. Belgrands project contemplated sinking wells or adits in the chalk, and obtaining therefrom what he terms "the subterranean reservoirs of water therein contained," artificial supplies, which would supply any deficiency in the quantity yielded by the streams. The works comprised what are termed conduits of derivation, being subsidiary conduits for collecting the waters from the various streams, and conducting them to the commencement of the main aqueduct that conveys the waters of the combined sources to Paris. The main aqueduct commences at a level of about 105 metres above the sea. It is a little over 180 kilometres in length (about 110 English miles), and terminates at Paris in service reservoirs at Belleville, at a level of 83 x metres above the sea. The subsidiary conduits are about 80 kilometres in length, and upon these and the main aqueduct there are seventeen bridges, 6 kilometres of conduit constructed upon arches, 7 kilometres of siphon piping, 28 kilometres of tunnel. The estimated cost of the ordinary works was about 19,000,000 francs, or £760,000, to which must be added about 2 1/2 million francs, or £100,000, for special works, where the aqueduct had to be constructed through difficult ground, and 4 1/2 million francs, or £180,000 for compensation to riparian owners on the streams which were selected as the sources of the supply, as well as to the owners of mills who might be injured by the abstraction of the water, and for the purchase of the lands through which the aqueduct had to be constructed; making a total estimated outlay on the works at the sources of the supply, and for the subsidiary and main aqueducts up to the distributing at Belleville, of 26,000,000 francs or £1,040,000.
The commission, to whom were referred all the projects which had been suggested, in their report, considered on the 18th of March 1859, recommended that the sum to be voted for the works should be 30,000,000 francs, or £1,200,000, thus increasing the estimate by 4,000,000 francs, or £160,000, with the view of providing ample means to cover any unforeseen works or difficulties which might be encountered during the carrying out of the project. The works have since that time been carried out substantially in accordance with the ideas and designs of Mr. Belgard, and under his direction and supervision; but they are not yet (1874) completed. The water from these sources is naturally very hard, but it is bright, fresh, and well aerated.
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