A smaller river flowing into a larger one is a tributary. The area of land drained by a river system— a river and all its tributaries—is that river’s watershed, also called a drainage basin. Landscapes determine where rivers flow, but rivers shape the landscapes through which they run as well.


A river that runs through a steeply sloped region and carries a great deal of sediment may flow as an interconnected series of watercourses called a braided river. In flatter regions, most rivers are meandering rivers. In a meandering river, the force of water rounding a bend gradually eats away at the outer shore, eroding soil from the bank. Meanwhile, sediment is deposited along the inside of the bend, where water currents are weaker.


Over time, river bends become exaggerated in shape, forming oxbows. If water erodes a shortcut from one end of the loop to the other, pursuing a direct course, the oxbow is cut off and remains as an isolated, U-shaped water body called an oxbow lake. Over thousands or millions of years, a meandering river may shift from one course to another, back and forth over a large area, carving out a flat valley. Areas nearest a river’s course that are flooded periodically are said to be within the river’s floodplain.