The Center for Earth and Environmental Science describes that floodplains are formed as rivers erode their own banks. Floodplains are the flat lands that lie adjacent to a river; they encompass the area that floods when the river's water level rises. As the river flows, it washes material downstream. When a flood occurs, this material is resuspended in the water and added to the floodplain.
According to The Center for Earth and Environmental Science, the ground underlying floodplains is largely composed of layers of silt, sand and mud. These layers are formed by periods of flooding, during which sediment is deposited on the floodplain, according to University of North Texas. During periods of flooding, some water is also absorbed by the floodplain soils. This prevents the flood from spreading further into the surrounding lands and causing erosion. This reserved water returns to the river during periods of lower water.
Floodplains are important to the natural environment for several reasons. According to The Center for Earth and Environmental Science, they provide habitats for numerous unique species of plants and animals. They also reduce the severity of floods and their effects on human developments, filter storm water and minimize water pollution from non-point sources.