Here's how it works:

* Erosion: Rivers flow over land, eroding the soil and rocks along their banks.

* Transportation: The eroded material is carried downstream by the river's current.

* Deposition: As the river's velocity slows down, the heavier sediments settle at the bottom, forming layers of alluvial soil. This happens particularly at bends in the river, at the river's mouth, or during floods.

Therefore, alluvial soil is essentially sedimentary soil formed from the deposits of rivers. It is known for its fertility, making it ideal for agriculture.