Aswan Dam - Irrigation Scheme

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 km³ water per year of which some 46 km³ are diverted into the irrigation canals.

In the Nile valley and delta, almost 33,600 square kilometres benefit from these waters producing on average 1.8 crops per year. The annual crop consumptive use of water is about 38 cubic kilometres. Hence, the overall irrigation efficiency is 38/46 = 0.82 or 82%. This is a relatively high irrigation efficiency. The field irrigation efficiencies are much less, but the losses are re-used downstream. This continuous re-use accounts for the high overall efficiency.

The following table shows that the equal distribution of irrigation water over the branch canals taking off from the main irrigation canals leaves much to be desired:

*) Period 1 March to 31 July. 1 feddan is about 1 acre or 0.42 ha.

*) Data from the Egyptian Water Use Management Project (EWUP)

Salt balance
The salt concentration of the water in the Aswan reservoir is about 0.25 kg/m³, a very low salinity level. At an annual inflow of 55 km³, the annual salt import reaches 14 million tons. The average salt concentration of the drainage water evacuated into the sea and the coastal lakes is 2.7 kg/m³. At an annual discharge of 10 km³ (not counting the 2 km³ of salt intrusion from the sea and the lakes, see figure "Water balances"), the annual salt export reaches 27 million ton. In 1995, the salt export was higher than the import, 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
Drainage through sub-surface 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 20000 square kilometres have been equipped with a subsurface drainage system and approximately 7.2 km³ 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 US$ 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