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The use of the Nile for irrigation, now regulated by the Nile Waters Treaty of 1959, dates back to at least 4000 B.C. in Egypt. The traditional system of basin irrigation : in which Nile floods were trapped in shallow basins and a cool-season crop of wheat or barley was grown in soaked and silt-replenished soil : has been replaced since the mid-1800s by a system of perennial irrigation and the production of two or three crops a year, including cotton, sugarcane, and peanuts. The delta barrages, just below Cairo, channel water into a system of feeder canals for the delta, and other barrages at Isna, Asyut, and Nag Hammadi keep the level of the Nile high enough all year for perennial irrigation in the valley of Upper Egypt; the Idfina Barrage on the Rashid prevents infiltration by the sea at low water. Nile water is also used for irrigation in the Faiyum Basin.
The Aswan Dam (completed 1902 and raised twice since then) was the first dam built on the Nile to store part of the autumn flood for later use; it has a storage capacity of 5 billion cu m and is now supplemented by the Aswan High Dam (completed 1971), 5 mi (8 km) upstream, with a storage capacity of 48 billion cu m, sufficient (with existing dams) to hold back the entire flood for later use. Construction of the Aswan High Dam has added c.1,800,000 acres (728,500 hectares) of irrigated land to Egypt's cultivable area and converted c.730,000 acres (295,400 hectares) from basin to perennial irrigation. Lake Nasser, created by the Aswan High Dam, has experienced problems with silting. There has been a reduction of soil replenishment downstream and a reduction of nutrients that once fed the E Mediterranean Sea. Other important storage dams, all outside Egypt, but built with Egypt's help or cooperation, are the Owen Falls Dam (1954) and Jabal Awliya Dam (1937) on the White Nile; the Sennar (1927) and Roseires (1966) on the Blue Nile; and the Kashm-el-Girba Dam (1964) on the Atbara River.
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