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). During the summer season 1½ to 1 million cubic metres per day (713 to 409 cubic feet per second). The ordinary and maximum and minimum levels of the Bahr Yûsuf are given in the list below:— --+--------------+--------------+----------------+------------------+-- | | Below Derût. | Above New | Below Old Bridge | | | | Bridge, Lahûn. | on Fayûm Side. | | +--------------+----------------+------------------+ | Flood season | 46·75 | 26·50 | 23·90 | | | | | | | Winter | 43·00 | 24·14 | 23·15 | | | | | | | Summer | 42·15 | 22·90 | 22·50 | | | | | | | Maximum | 46·95 | 27·80 | 23·90 | | | | | | | Minimum | 41·67 | 22·50 | 22·27 | --+--------------+--------------+----------------+------------------+--