The stream slows down and spreads out on the flatter ground
Often, flood plains are where the most fertile soil is. The rich alluvial soil washes down from mountains in rivers and streams, bringing with it rich nutrients which are perfect for growing crops. Flood plains, being close to rivers, also offer easy transportation of goods up and down waterways.
from streams and rivers that flow down mountains
The Rocky Mountains lie just west of the Great Plains. They stretch from Canada down to New Mexico and are known for their rugged terrain and diverse ecosystems. The Rocky Mountains act as a natural barrier between the Great Plains and the western states.
The Interior Plains are located in the central part of North America, between the Rocky Mountains and the Appalachian Mountains. They stretch from Canada down to the Gulf of Mexico.
The geography in North Carolina is varied. There are coastal plains, the plains and the mountains. As you drive around the state, elevation goes up and down.
The broad flat valley floors that are carved out by wondering streams are called flood plain and the two methods of the streams eroding the rocks to form the flood plain are down cutting and lateral erosion.
Tiny remains of animals and plants in streams come from the mountains. When it rains, these remains are washed down the mountains toward the streams.
By two tectonic plates clashing against each other, forcing them either up or down
The rivers, after descending from the mountains deposit pebbles in a narrow belt of about 8 to 16 km in width lying parallel to the slopes of Shiwaliks. It is known as Bhabar. All the streams disappear in this Bhabar belt.
Plains receive eroded minerals from higher elevations, and erosion does not remove as much dead plant material as it does from hills and mountains. Precipitation tends to percolate minerals down into the soil.
Centuries of erosion carried soils, water, and nutrients down from the higher slopes.
I think you mean form. And it forms from rain. Rain is always not responsible for the the formation of rivers. Rivers originate from mountains and the point from which they originate is called the source. The snow in the mountain tops melts during the summer and flows down the mountains in form of small streams. As it flows down, it collects more water/snow and keeps flowing down. By the time it reaches the plains, it is filled up with lots of water, impurities, and life forms. This is how rivers are formed and other factors like rain also contribute to their formation.