An alluvial plain is a flat area of land that is formed by the deposition of sediment carried by rivers and streams. These sediments, which include sand, silt, and clay, are deposited when the water slows down, creating fertile soil that is ideal for agriculture. Alluvial plains are often found near riverbanks and deltas, where water flows into larger bodies like lakes or oceans. These plains are important ecosystems that support diverse plant and animal life. They are also significant for human activities, as many civilizations, such as those along the Nile River and the Indus River, have thrived in these fertile regions due to their rich resources.