For centuries, the annual floods of the Nile, Tigris, and Euphrates, for example, have brought fertile silts and water to the inhabitants of their lower valleys.

比如，几个世纪以来，尼罗河、底格里斯河和幼发拉底河每年的洪水给下游山谷的居民带来了肥沃的淤泥和水源。