Theory question 107
Geography of Africa(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) Highlight four problems associated with this type of agriculture in the Nile Valley
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(a) Basin irrigation: flood water is trapped in walled basins during the annual flood and crops are planted when it drains, one crop a year. Perennial irrigation: dams and barrages (Aswan, Sennar) store water that flows through canals all year, allowing two or three crops. Also shaduf, sakia (water wheel) and pumps lifting water.
(b) Very low rainfall (desert climate); reliable water from the Nile; flat fertile alluvial land; large population needing food; cash crops for export (cotton, sugarcane); government investment.
(c) Salinisation and waterlogging; silting of reservoirs and canals; water-borne diseases (bilharzia); loss of fertile silt below dams; fluctuating water levels; displacement of people; pests.
Describe how water reaches the fields in each method.