Page "Geography of Egypt" Paragraph 15

The Blue Nile has a similar pattern.

It contributes 17 % of the Nile's waters in the low-water season and 68 % during the high-water season.

In contrast, the White Nile provides only 10 % of the Nile's waters during the high-water season but contributes more than 80 % during the low-water period.

Thus, before the Aswan High Dam was completed in 1971, the White Nile watered the Egyptian stretch of the river throughout the year, whereas the Blue Nile, carrying seasonal rain from Ethiopia, caused the Nile to overflow its banks and deposit a layer of fertile mud over adjacent fields.

The great flood of the main Nile usually occurred in Egypt during August, September, and October, but it sometimes began as early as June at Aswan and often did not completely wane until January.