(a) Name any four irrigation areas in the Nile Valley. (b) Describe the perennial method of irrigation in the Nile Valley. (c) Explain any four problems cre...

(a) Four irrigation areas in the Nile Valley

• The Nile Delta (Lower Egypt, around Cairo/Damietta/Rosetta branches).
• The Faiyum (Fayoum) Depression.
• The Gezira Scheme in the Sudan (between the Blue and White Nile).
• Upper Egypt around Aswan and the area behind the Aswan High Dam (Lake Nasser).

(Other acceptable areas: the Middle Egypt reaches around Asyut; the New Halfa scheme.)

(b) The perennial method of irrigation in the Nile Valley

Perennial (all-year) irrigation is the modern system in which water is stored and supplied to the land throughout the year, so that two or three crops can be grown annually instead of one.

• Large dams and barrages (for example the Aswan High Dam) are built across the Nile to hold back the flood water in a reservoir such as Lake Nasser.
• The stored water is released steadily and led away by a network of main and branch canals which distribute it to the fields all through the year.
• Water is lifted to the fields where necessary by devices such as the shaduf, sakia (water-wheel) and Archimedean screw, or by mechanical pumps.
• Because water is available at all seasons, the farmer no longer depends on the natural annual flood, and the land is cropped continuously.

(c) Four problems created by irrigation in the Nile Valley

• Salinity (salinisation): constant watering without natural flushing leaves salts in the soil as the water evaporates, reducing fertility.
• Waterlogging and rising water table: excessive irrigation raises the water table and floods the root zone, harming crops.
• Loss of natural silt/fertility: the dam traps the fertile silt behind it, so farmers must now buy expensive artificial fertilisers to replace it.
• Spread of water-borne diseases: permanent standing water in canals encourages bilharzia (schistosomiasis) and malaria, and also allows aquatic weeds to choke the canals.