It is the flood plain.
It is called the flood plain.
A flood plain is a flat or gently sloping area near a river or stream that is prone to flooding. It forms when the river overflows its banks and deposits sediment on the adjacent land. Over time, this repeated flooding creates the flat surface of a flood plain.
A flood plain is an area adjacent to a river which regularly floods when that river's water rises "above flood stage." It can include areas great distances away from the river's course (see significant Mississippi flooding), but are usually confined to areas proximate to the usual course.
A plain is basically a large, flat area and flood plains are the large flat areas to either sides of rivers. These areas, when it rains so much that the river bursts its banks, are covered in water: flooded.
It's called a 'flood plain'.
It would be the flood plain or meander belt.
The flat, wide area along a river is called its flood plain. This is sometimes part of a larger area called the alluvial plain, which formed as the river shifted over time and deposited soil when it flooded.
Flood plain
The mature stage of river development is characterized by flat flood plains where the river meanders and deposits sediment. In this stage, the river has a large volume of water and is more stable, leading to the creation of wide flood plains.
The floodplain is an area of flat land found on either side of a river that usually becomes wider as the river nears its mouth. A low watery formation of land at the mouth of a river is called a delta.
A plain is basically a large, flat area and flood plains are the large flat areas to either sides of rivers. These areas, when it rains so much that the river bursts its banks, are covered in water: flooded.
Flood plain