Landform

The ability of water to move sediment depends on its velocity, which is related to the slope of its bed. When it is moving rapidly it can transport a great deal, but if it slows down it deposits its load. High in the mountains the gradient is steep and erosion dominates. Rivers actively cut downward, and mass wasting adjusts the walls to a "V" shape. These valleys intersect in a branching network as tributaries merge to form fewer, larger streams. As the water moves downstream the slope of its bed decreases and eventually a steady state develops where there is little down cutting. Here the slopes continue to retreat until a gentle, rolling topography evolves. Further downstream the slope of the bed is even less, and deposition begins to dominate. Here the river deposits much of its load during times of flooding, and modifies these deposits the rest of the time. One distinctive landform resulting from this is the meander. As the river winds back and forth across its flood plain it erodes on the outside of each sinuous curve, the cut bank, and deposits material on the inside, the point bar. Eventually the river flows into a standing body of water, either a lake or the sea, and slows down even more, depositing its sediment in deltas. These landforms emerge if the level of the lake or sea goes down.