What events led to the development of flood planes and deltas?

Floodplains and deltas are formed through sediment deposition by rivers during periods of flooding. When a river overflows its banks, it spreads out and slows down, causing sediment to settle on the surrounding land, creating a floodplain. Deltas develop at river mouths where sediment carried by the river is deposited as the water slows upon entering a larger body of water, such as an ocean or lake. Over time, these processes build up layers of fertile soil, making these areas crucial for agriculture and biodiversity.