The earth developed on flood plains and deltas, having only the characteristics of the clay, silt or gravel carried by rushing streams and deposited where the streams slow down: The alluvial soils leave a fine-grained earth material consisting of very tiny particles of sand and clay, all of which are deposited by water flowing over flood plains or into river beds.

Keith and the other farmers near the mouth of the river found that the alluvial soils were much more fertile than the land farther away from the river.

Fine-grained fertile earth deposited by water flowing over flood plains or in river beds: Keith and the other farmers near the mouth of the river found that the alluvial soils were much more fertile than the land farther away from the river.

Alluvial soil is rich and fertile earth and can be found in aquatic communities (living in or on water and is a substantial part of the life span and is generally restricted to fresh water or inland waters).