Sennar dam during construction, Sudan, 1924.
© Science Museum / Science & Society Picture Library
Photograph. Completed in 1925, the Sennar Dam was built to improve the supply of water from the Blue Nile for irrigation of cotton plantations in Sudan. The Blue Nile has its headwaters in the highlands of Ethiopia and is subject to large seasonal variations in its flow, producing the floods for which the Nile has historically been notorious in September.