Plate II.
BRIDGE CARRYING THE BAZAAR STREET, MEDINET EL FAYÛM, OVER THE BAHR YÛSUF.
Of the Bahr Yûsuf before the Ibrahimîyah Canal was made, M. Linant remarks in the same Mémoires, that “it is the only canal in Egypt which, without receiving water from the river during the summer, nevertheless has enough to serve for the irrigation of the Fayûm from the springs in its bed.” These springs still supplement the summer supply of the Fayûm by adding to the discharge, which is apportioned to the Bahr Yûsuf at Derût, about a quarter of a million cubic metres a day (102 cubic feet a second).
During the summer and winter the water of the Bahr Yûsuf is (with the exception of an insignificant quantity lifted for the irrigation of small areas at different points along its course) reserved for the Fayûm, but during the flood season its channel is used to carry water for the inundation of the lands on both sides of it, and later it is made use of as the channel of discharge for the basins which it has filled, or helped to fill.
At Lahûn, where the Bahr Yûsuf turns into the Fayûm, the quantity of water admitted is controlled by two regulators. The lower bridge is a very ancient one ([frontispiece]), of what date is unknown. Its floor in Linant Pasha’s time had already partly given way, but from his description it would seem to be now in the same state in which it was more than twenty years ago. The upstream half has evidently been added to the downstream half, as there is a clean line of separation in the middle of the length of the present archway. This is only to be seen by entering the passage below the arches, as the junction is not visible from above.
In 1838 Linant Pasha caused the second regulator of three openings (two of three metres’ and one of four metres’ span) to be constructed as a precaution 80 metres above the old one, and it was a very wise precaution to take. The head of water is now divided between the two bridges so that the action is less severe than it was before the second bridge was constructed.
The present discharges passed by these regulators into the Fayûm are:—
During the flood season 6½ to 7 million cubic metres per day (2658 to 2863 cubic feet per second).
During the winter season 3 million cubic metres per day (1227 cubic feet per second).