(a) Describe two methods of irrigation agriculture in the Nile Valley (b) Give three reasons for the development of irrigation agriculture in this region (c...

(a) Two methods of irrigation agriculture in the Nile Valley

1. Basin (flood) irrigation: low earth banks divide the flood plain into large basins. During the annual flood, river water is led into the basins and allowed to stand for several weeks so that it soaks the soil and deposits fertile silt; the surplus is then drained back and crops are sown on the moist land. This is the older, traditional method.
2. Perennial (canal) irrigation: water is stored behind dams and barrages (for example the Aswan High Dam) and released all year through a network of canals to the fields. Water may be lifted onto the land by the shaduf, sakia (water wheel) or Archimedes screw, or nowadays by mechanical pumps and modern canal/sprinkler systems, allowing two or more crops a year.

(b) Three reasons for the development of irrigation agriculture in this region

1. The region has a hot desert climate with very low, unreliable rainfall, so farming is impossible without added water.
2. The Nile provides a permanent, dependable supply of water fed from distant rainy highlands, guaranteeing water even in the rainless valley.
3. The valley has fertile alluvial silt and a large population that must be fed, so intensive irrigated cropping (cotton, rice, sugar cane, cereals) is worthwhile.

(c) Four problems associated with irrigation agriculture in the Nile Valley

1. Salinisation and waterlogging of soils where drainage is poor and evaporation leaves salts behind.
2. Loss of natural silt fertility below the Aswan Dam, forcing farmers to buy expensive artificial fertilisers.
3. Spread of water-borne diseases such as bilharzia (schistosomiasis) and malaria that breed in the standing canal water.
4. Silting of canals and reservoirs, plus high cost of maintaining dams, pumps and canals, and pressure of population on the limited irrigated land.