Sediments building up don't directly create farmlands. They contribute to the formation of fertile land over long periods, but the process is much more complex and involves several other factors.

Here's how it works:

1. Sediment Deposition: Rivers, wind, and other natural forces carry sediments (like silt, clay, and sand) and deposit them in various locations, including floodplains, deltas, and coastal areas.

2. Formation of Alluvial Soil: Over time, these deposited sediments decompose and mix with organic matter, creating a rich, fertile soil called alluvial soil. This soil is typically deep, well-drained, and rich in nutrients, making it ideal for agriculture.

3. Land Formation: In some cases, these sediment deposits can gradually build up land, forming new areas suitable for farming. This process is particularly evident in river deltas and floodplains.

4. Human Intervention: While natural processes lay the foundation, humans play a crucial role in transforming these fertile areas into farmlands. They clear vegetation, build irrigation systems, and cultivate crops to create agricultural land.

Therefore, it's not the sediment buildup itself that directly creates farmlands, but rather the combined action of sediment deposition, soil formation, and human intervention.

Examples of farmlands formed through this process:

* The Nile River Valley: The annual flooding of the Nile River deposits rich sediment, creating fertile land for agriculture.

* The Mississippi River Delta: The delta formed by sediment deposition is home to vast farmlands producing crops like rice and cotton.

* The Yellow River Valley: The Yellow River, known as China's "Mother River," has deposited a thick layer of sediment, creating fertile land for agriculture.

These examples illustrate how sediment buildup contributes to the creation of fertile soil, which, with human intervention, can be transformed into productive farmlands.