When a flood plain is not flooded it may be good farm land

A floodplain is the flat area around a river that is covered in times of flood. A floodplain is a very fertile area due to the rich alluvium (fine sediment) deposited by floodwaters. This makes floodplains a good place for agriculture. A build-up of alluvium on the banks of a river can create levees, which raise the riverbank.