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Irrigation scheme

Due to the absence of appreciable rainfall, Egypt's agriculture depends entirely on irrigation. With irrigation, two crops per year can be produced, except for sugar cane which has a growing period of almost one year.

The high dam at Aswan releases, on average, 55 cubic kilometres (45,000,000 acre⋅ft) water per year, of which some 46 cubic kilometres (37,000,000 acre⋅ft) are diverted into the irrigation canals.

In the Nile valley and delta, almost 336,000 square kilometres (130,000 sq mi) benefit from these waters producing on average 1.8 crops per year. The annual crop consumptive use of water is about 38 cubic kilometres (31,000,000 acre⋅ft). Hence, the overall irrigation efficiency is 38/46 = 0.826 or 83%. This is a relatively high irrigation efficiency. The field irrigation efficiencies are much less, but the losses are reused downstream. This continuous reuse accounts for the high overall efficiency.

The following table shows the distribution of irrigation water over the branch canals taking off from the one main irrigation canal, the Mansuriya Canal near Giza.

The salt concentration of the water in the Aswan reservoir is about 0.25 kilograms per cubic metre (0.42 lb/cu yd), a very low salinity level. At an annual inflow of 55 cubic kilometres (45,000,000 acre⋅ft), the annual salt influx reaches 14 million tons. The average salt concentration of the drainage water evacuated into the sea and the coastal lakes is 2.7 kilograms per cubic metre (4.6 lb/cu yd). At an annual discharge of 10 cubic kilometres (2.4 cu mi) (not counting the 2 kilograms per cubic metre of salt intrusion from the sea and the lakes, see figure "Water balances"), the annual salt export reaches 27 million ton. In 1995, the output of salt was higher than the influx, and Egypt's agricultural lands were desalinizing. Part of this could be due to the large number of subsurface drainage projects executed in the last decades to control the water table and soil salinity.

Drainage through subsurface drains and drainage channels is essential to prevent a deterioration of crop yields from waterlogging and soil salinization caused by irrigation. By 2003, more than 20,000 square kilometres (7,700 sq mi) have been equipped with a subsurface drainage system and approximately 7.2 square kilometres (2.8 sq mi) of water is drained annually from areas with these systems. The total investment cost in agricultural drainage over 27 years from 1973 to 2002 was about $3.1 billion covering the cost of design, construction, maintenance, research and training. During this period 11 large-scale projects were implemented with financial support from World Bank and other donors.