The distance from Lahûn to the end of the Bahr Yûsuf at Medineh along the canal is 24 kilometres (15 miles). Between kilometre 11 and 14 the bed is rock, the highest point of the bed being at R.L. 21·00 and between kilometre 12 and 13. The bed elsewhere is generally between R.L. 17 and 19.
At kilometre 10·130, the Bahr (canal) Sêlah takes off on the right, and after flowing by the Hawârah pyramid and passing under the Fayûm railway, its water surface comes level with the soil and irrigates the strip of land bordering the Fayûm depression on the right of the main drainage line on this side.
Similarly at kilometre 15·5 the Bahr Gharaq takes off on the left of the Bahr Yûsuf, and, aided by the Bahr Qalamshah, irrigates the east slope of the Fayûm and the whole of the Gharaq Basin. The strip on the left of the south main drainage line, forming the sloping side of the Fayûm Basin on the south, is irrigated by the Bahr Nezlah, which takes off from the main canal at kilometre 16·370.
With the exception of the Bahr Tamîyah, which flows in the channel of the north-east main drain itself and irrigates the distant north corner of the province on the right of the drain, all the other canals irrigate the central part of the Fayûm, which lies between the two main drainage lines. These canals may be divided into three classes corresponding to the three plateaux:—
1. The short and high level canals irrigating the high land on both sides of the Bahr Yûsuf and round Medineh, roughly speaking all lands down to contour R.L. 18·00.
2. The medium canals, which irrigate between R.L. 18·00 and 10·00 or thereabouts.
3. The long ravine canals, which carry water to the distant parts of the Fayûm below contour R.L. 10·00.
In a lawless province like the Fayûm, such an arrangement of canals is of great assistance in the equal distribution of water to all parts of the province. The long canals of class 3 are, in their upper reaches, so far below the cultivated surface of the soil, that no crop-owner of the first and second plateaux would attempt to irrigate from them except by means of water-wheels, which have to be regularly licensed. The canals of the 2nd class are intermediate in level and length between the first and third, and do not conveniently irrigate, except at some considerable distance from their heads.
There is a further advantage gained by the water of the long canals falling at once to low levels at their commencement. Along the margins of the Bahr Yûsuf and round about Medineh is a considerable area of valuable land above the highest level reached by the water in the parent canal. To irrigate this, water is lifted in pitchers fastened to the side of the outer edge of undershot wheels, which are turned by the force of the water descending to the low-level beds of the ravine canals. These wheels turn day and night without ceasing, so long as there is sufficient water. A head of 25 centimetres is sufficient to turn an ordinary wheel which lifts the water about 2 metres, but when greater heads are obtainable, water is lifted in this way as much as from 4 to 6 metres ([Plate IV.]) A fall of 80 centimetres will work two wheels, one behind the other, which lift the water 5 metres.
The channel, carried by the imposing looking aqueduct of [Plate IV.,] is only 40 centimetres wide by 30 centimetres high, the whole thickness of the aqueduct being only 85 centimetres. The expense, incurred in building it, points to the value of a constant stream of water raised in this manner.