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.
The floodplain.
flood plain
delta
Aquifer
planes
lava plateau
If you are referring to the crossword puzzle hint, the answer is probably prairie.
russia is the largest flat land in the world.
Fertile soil is one aspect of flat land in Egypt
Plateau.
Plains
TeNnes
A plain is a wide area of flat or gently rolling land. Plains cover more than one-third of the world's land area. They exist on every continent.
its a streem
its a streem
landscape
Mud Slide
planes
lava plateau
A plain or Grassland
I think you mean a plateau. Plateau: expanse of raised land with a level surface. Also known as tableland, do to the flat tops.