After 1861 all-year-round irrigation increased rapidly in Egypt for economic
as well as for political reasons after the completion of the great delta weir
of Al-Qanatir al-Khayriya at the Nile fork north of Cairo. Its construction
was started during the reign of Mohammed Ali (1805–48) with the intention
of extending the area cultivated with cotton, for which there existed a great
demand in England at the time, imports from America having stopped owing
to the Civil War there. The construction of the first big dam at Aswan in
1902, however, was decisive for the introduction of all-year-round irrigation.
The dam was heightened in 1912 and 1933, so that a storage capacity of 5.3
billion m3
 was finally reached. The water stored annually in autumn served
for irrigation purposes in spring and summer, when the Nile water level was
low. During the main Nile swell from August to October the 180 floodgates
of the dam were opened. They were closed only after the water level had
fallen again. In this way the main Nile flood, which is heavily laden with
the silt introduced by the Blue Nile, could pass through, thus preventing
siltation of the reservoir. Simultaneously further dams were built in various
other parts of the Nile course. Their main purpose was to lift the water
locally, so that it could be led into the corresponding irrigation canals, as, for
example, the Ibrahimiya Canal, or the Bahr Yusif Canal, which branches off
from it. Mainly on the basis of the dams described, irrigation took place on
83.2 per cent of Egypt’s arable land all year round in the 1960s