Watershed
the area from which water drains into a river is called the river's catchment. A river's watershed is the connecting ridges surrounding the watershed, and separating it from adjacent ones.
The River Kwai is about 236 miles in length. It is known in Thailand and the surrounding area as Khwae Yai River.
No not every river IS a catchement. Although, yes every river does have a catchment area. The catchment area is the surrounding land within a watershed in which a single river system drains.
The area surrounding a river or coast (riparian zone or area) are "Auengebiet" in German. If referring only to a river area it could also be called "Flussauen"
Sams Club
It will result in flooding of the surrounding area.
The flood plain
The Niger River helped shape the surrounding area in Medieval times because it offered a source of water for the area. People were able to grow crops near the river and had access to fresh water.
Well if your question is "what happens when a river overflows its banks" Then my answer is simple, it floods. A river overflows when extra or excessive water is added e.g. prolonged percipitation(rainfall). Or another case would be pressure added in a section of the river causing the eureka theory and the water level will rise causing an overflow. This simply leads to a flooding of the surrounding area ,depending on the volume of water and the terrain surrounding determines the spread of flooding.
sahara ,sahel, Savannah, rain forest
Niagara River