A type of azonal *soil
formed on the flood plains of river valleys and at river mouths (alluvial fans or deltas). New material is successively deposited on the surface when the land is subjected to flooding. In tropical regions such areas may be used as paddy fields, and in arid regions the extent of the alluvial soils may be artificially increased by irrigation methods, as along the banks of the Nile. The polders of the Netherlands are reclaimed marine alluviums.