Aswan Dam have been flooded by Lake Nasser. Before the construction of the High Dam, the Nile deposited sediments of various particle size – consisting of fine sand, silt and clay – on fields in Upper Egypt through its annual flood, contributing to soil fertility. However, the nutrient value of the sediment has often been overestimated. 88 percent of the sediment was carried to the sea before the construction of the High Dam. The nutrient value added to the land by the sediment was only 6,000 tons of potash, 7,000 tons of phosphorus pentoxide and 17,000 tons of nitrogen. These amounts are
Aswan Dam year. The annual crop consumptive use of water is about . 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 reused downstream. This continuous reuse 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 one main irrigation canal, the Mansuriya Canal near Giza, leaves much to be desired: The salt concentration of the water in the Aswan reservoir is about , a very low salinity